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BMS Tropical Update – August 13th

It’s been a while since the last BMS Tropical Update on July 11. That update focused on Tropical Storm Barry, which eventually made landfall along the central Louisiana coastline as a minimal Category 1 hurricane. Even though it was a disheveled mess of a storm, it still caused nearly $100 million of insurance industry loss in Louisiana and set an Arkansas state rainfall record of 14.58” near Murfreesboro, Arkansas. Luckily, this large amount of rain did not fall along the Mississippi River in southern Louisiana, which was at already historic high levels along many sections, including levy-protected New Orleans. With Barry’s landfall, it joined 12 other July hurricane landfalls in the Gulf of Mexico since 1900. However, as we look forward to the remaining months of the hurricane season, it’s worth noting that there is no correlation between hurricane activity occurring before August and how much activity will be seen during the remainder of the season.

By now you may have seen the various updated Atlantic hurricane season forecasts, which, for the most part, continue to call for above-normal activity. As I have stated several times, the overall number is not what is important, but, rather, the steering currents that influence the track(s). Contrary to popular belief, however, most named storms have fairly regular and well-defined tracks because of the location and orientation of the Bermuda Azores high pressure, which ultimately determines the tracks of most named storms. The difficulty in predicting a storm track occurs either when the typical climatological steering wind flow is replaced by a less common, large-scale flow or, even more importantly, when rapid changes occur in the strength and orientation of the steering current, such as a bypassing mid-latitude trough, which is really only well-forecasted 5 to 7 days in advance.

Above is the current steering flow across the Atlantic Ocean. Note the current weakness across the Bermuda Triangle. Absent any mid-latitude system, this would likely be the path for named storms out of the deep tropics.

The average date for the formation of the season’s third named storm is August 13, and the average date for the second hurricane is August 28, so there is nothing unusual about having a calm spell this time of year like we’ve seen recently. There have been several tropical waves that have propagated from the African coastline, and a few of these have been watched by the National Hurricane Center. Tropical Depression Three, which formed for less than 24 hours off of the eastern coast of Florida, provided a glimpse of where named storms could track this season if the current North American and Atlantic pressure patterns hold into the peak of the hurricane season. However, first let’s determine the factors to consider for the remainder of the hurricane season and then worry about the steering current once the storms begin to form. In the beginning of the season, it was suggested that named storms would form closer to the U.S. coastline rather than in the Main Development Region, and track closer to the eastern coast of the U.S. with the overall season seeing more back half activity.

Although many of the headlines suggest that an above-normal season is yet to come, these headlines should probably be taken with a grain of salt. Take the NOAA forecast, for example. There is a 45% probability of an above-normal season, which obviously means there is a greater chance of a normal to below-normal season at 55%. In fact, I don’t think there is much confidence in the August activity forecasts, even though they are usually the most accurate when it comes to the overall Atlantic Basin activity.

There are a number of reasons why there is a lack of confidence in the forecast:

Unfortunately, even with the more reliable August forecast, there are still a lot of variables for the remainder of the season. Perhaps the best guidance would be to view the analog years, which serve as a guide for potential activity and possible tracks for the remainder of the season.

Above are the various analog years (1991, 2012, 2014, 2015) which may best indicate the current conditions and possible track of storms this season. Depending on the overall timing of development, analyzing these years may provide a guide as to the general track storm could take this season, but the timing of mid-latitude weather systems will determine the steering level winds if they reach the U.S. coastline. Example: Isaac or Sandy 2012 (Remember Sandy could have also turned out to sea)

This week we may see the remnants of an old stalled front off of the eastern coast of the U.S., providing a chance at tropical cyclogenesis closer to home. Hopefully, there won’t be a need for too many BMS Tropical Updates over the next 30 days, will be keeping an eye on how any potential events could impact the insurance industry.

BMS Tropical Update July 11th

As mentioned in the last BMS Tropical Update, a storm is brewing in the Gulf of Mexico.  The National Hurricane Center has now named this system Tropical Storm Barry and expects it to potentially become a hurricane by Saturday and make landfall shortly thereafter, with possible impacts along the coasts of Texas and Louisiana, particularly in the city of New Orleans.  As many already know, New Orleans sits below sea level and has had its share of flooding problems in the past.  Since water is the new wind risk for the insurance industry, this BMS Insight will focus on this threat in a bit more detail, as any wind damage at this time is uncertain given the high forecast uncertainty around the overall intensity and track of the storm.

The forecast models are suggesting as much as 18 inches of rain for the region, which isn’t good, considering that the area is already inundated with rain. New Orleans has already flooded this week from rain, with many streets covered with a dangerous amount of water.  The Mississippi River is expected to rise to 19 or 20 feet by the weekend, which is near the height of the city’s levees.

By Saturday, it may have winds of 85 mph, making it a Category 1 hurricane on the Saffir-Simpson wind scale.  It should be noted, however, that there is a lot of uncertainty around the forecasted intensity of the storm. This intensity will depend on how much wind shear the storm encounters and how much time it spends over the warm waters of the Gulf of Mexico.  Currently, the worst-case scenario appears to be a Category 1 hurricane.  However, forecasts can change fast, as we experienced with Michael last year.  Most of the model guidance is suggesting a lopsided tropical storm with a landfall somewhere along the Louisiana coastline.

Wind speed is just one of the insured loss concerns from the storm.  Historically, flooding has not been a big concern for the insurance industry, but the take-up rates of flood insurance are higher in Louisiana, including New Orleans.  The reinsurance markets are taking on some of the risk from the National Flood Insurance Program, so this flood risk needs to be watched.  Also, coastal flooding tends to be the deadliest aspect of a hurricane.

The main concern here is that the storm surge combined with heavy rainfall could reach 3 to 5 feet, which would flood many of the low-lying areas of Louisiana.  This storm is expected to generate a lot of rain, with some areas potentially seeing more than a foot, which can contribute to inland flooding along the banks of rivers.

This is the current National Weather Service rainfall forecast over the next 7 days. This rainfall forecast will depend highly on the track of Barry
Current National Weather Service Forecast river level in New Orleans. This forecast will change with the track and intensity of Barry

The biggest threat from the storm may be in New Orleans, where the Mississippi River is already at 16 feet due to the very wet spring and summer upstream.  Some states along the river have seen their wettest spring in recorded history.  All of this water has worked its way down the Mississippi River, which has been high for well over a month now.  The National Weather Service is now predicting the river to crest at 19 feet on Saturday.  That is one foot below the top of the river levees. This could change given the track of the forecast. This morning the forecasted river height was 20 feet, so the forecast is changing for the better since the newest forecast is now one foot below the top of some of the levees.

So, why is this a concern?  During both Hurricane Katrina in 2005 and Hurricane Isaac in 2012, storm surge pushed well upriver. In those cases, however, the river was only at a level of 3 feet or less.  During Katrina, a Category 3 hurricane with top winds of 125 mph, the river swelled to at least 15.25 feet at the Carrollton Gage in New Orleans.  The gage stopped operating when the water reached that level.  Several barges were deposited on top of the levees in Plaquemines Parish during the storm by surge water.  During Isaac, a Category 1 hurricane with top winds of 80 mph, the river rose to 9.5 feet at the Carrollton Gage.  While the current river level in New Orleans is 16 feet, levees and floodwalls protect the city up to water heights of about 20 feet.

How high is a 20-foot-high river stage for New Orleans?  It is higher than 99.9% of the city’s land surface, higher than every human being except those in multi-story buildings and about 30 feet higher than the lowest neighborhoods.

The red dots show where levees in New Orleans are under 20 feet.  This is where over-topping of levees is most likely if the forecast of 19 feet comes to fruition on Saturday. The red dots on the north side of the Mississippi River flooded during Katrina, including the Lower 9th Ward.
These are the areas of New Orleans that flooded during Katrina.

In summary, the precursor for a bad flooding event is set for New Orleans and remains for much of the hurricane season.  Many areas of Louisiana are flat, and flooding is a big concern with this upcoming storm.  There is uncertainty at this time around the potential strength and track of the storm, which also increases the level of uncertainty around the storm surge that may be expected.  However, the rainfall forecasts have been fairly consistent over the last several days, with most of the heaviest rain expected to fall along with the storm’s forecasted path.

BMS Tropical Update: July 9th

There is an old proverb used to describe the Atlantic hurricane season: “June – too soon; July – stand by; August – come they must; September – remember; October – all over.” In fact, we suggested in our May BMS Tropical Insight that the next best opportunity for tropical storms was going to be in early July. It appears that June was indeed too soon for tropical threats to the U.S. coastline. However, with the start of July, that is expected to change with development appearing likely in the northern Gulf of Mexico later this week and into the weekend.

The NHC is giving an 80% chance of a Tropical depression forming in Gulf of Mexico later this week.


A precursor vorticity center (areas of spin) is currently heading south through Georgia and will emerge into the northeast Gulf of Mexico by Wednesday. This circulation will take advantage of warm water in the area to build thunderstorms and may slowly intensify into a tropical system.
Dry air and dust from a few major outbreaks of Saharan dust have battered most of the Atlantic basin for the last several weeks. This combined with strong wind shear has prevented tropical development across the Atlantic basin since Subtropical Storm Andrea briefly roamed the waters of the west-central Atlantic in late May.

With the Madden-Julian Oscillation (MJO) currently in a positive phase that supports upward motion over Central America, the absence of strong wind shear and warmer than normal waters across the Gulf of Mexico, it should not take much to organize a tropical named storm which, if it develops later this week, will be named Barry. For the last several days, the forecasted steering winds have suggested that any named storm would drift toward the central and western portions of the Gulf of Mexico this weekend. This would give it more time over open water and could potentially create a stronger storm. With this track the risk to the insurance industry grows due to the large amount of exposure in the Houston areas, the risk to offshore assets increases due to a number of petroleum rigs and refineries along the central and western Gulf Coast. Regardless of how much development we see, the forecast models are suggesting multiple days of showers and thunderstorms that could potentially bring flooding to the southern Plains, lower Mississippi Valley and/or the southern Appalachians starting this weekend and into next week, depending on the track and timing of the storm. Some models take the tropical storm as far west as Houston which has no issue flooding from even the smallest of weather systems. Currently, some of the guidance calls for 15″ of rain over the next 7 days for the area.

The overall model guidance from the ECMWF and GFS models have been back and forth over the last few days and the landfall location as suggested by the above GFS ensembles is anywhere from east Texas to Louisiana. Keep in mind this entire area will see a lot of rain.
Source: https://www.tropicaltidbits.com


The last time a named tropical system made landfall in the U.S. during the month of July was Tropical Storm Emily of 2017. Emily formed in the eastern Gulf of Mexico and moved into the central Florida Peninsula on the last day of July, so it’s not unusual to see the forecast of such an event happening this week. As I mentioned in our May BMS Insight, it appears that this season’s tropical activity will be more likely to develop closer to the U.S. coastline instead of out in the Main Development Region (MDR) of the Atlantic Ocean. The bigger question is just how much activity we’ll see this season as we move toward its climatological peak at the beginning of September.


Forecasters continue to call for five to eight hurricanes to develop this season. July still does not look like a very active period for named storm development, as large scale sinking air will continue over much of the Atlantic basin, along with on and off bursts of Saharan dust that may keep activity to a minimum. While El Niño conditions may suppress the total number of tropical storms and hurricanes in the Atlantic basin this season, the data is suggesting that El Niño is weakening and may become a non-factor as we head into September. With the warmest ocean temperatures right along the U.S. coastline, the insurance industry should continue to watch for tropical waves coming off Africa which could potentially strengthen into named storms when they get closer to the U.S. coastline versus the MDR in a more typical season.

Above are the different phases of the MJO and the influence on precipitation. Notice the red circled areas above. Tropical cyclones making landfall along the Gulf Coast during Phase 2 of the MJO during meteorological summer causes a statistically-significant positive precipitation anomaly to show up in the Deep South in the 1979-2008. Research here by Zhou et al.
Notice how the red circled areas match the forecasted areas for heavy rainfall over the next 5-7 days along the Gulf Coast.

We are also now in the period where the insurance industry can begin to watch the subseasonal forecast. I have mentioned before that one of the best ways to predict this is to use the MJO, which is a pulse of upward motion that travels the tropics but also creates areas of sinking stable air in other parts of the tropics. This symbiotic pattern of wetter and drier areas moves east as a unit and typically completes a full cycle in 45 to 60 days. When the MJO (or similar phenomena) promotes upward motion over the Atlantic, hurricane development and rapid strengthening becomes much more common. According to research performed by Phil Klotzbach of Colorado State University, hurricane damage in the U.S. during convectively active phases of the MJO since the early 1900s is nearly three times greater than during suppressed Atlantic phases.


Therefore, I believe the next round of tropical storms may begin during the second week of August. Based on the current state of African waves and favorable conditions for development along the U.S. coastline, we may also be seeing an active late September and early October. Until then, keep watching the skies off the Gulf Coast and along the southeastern U.S. for the development of named storms that might not coincide with the MJO phases.

BMS Tropical Update: 10/11/2018 11 AM CDT

Hurricane Michael became the most intense hurricane on record to strike the Florida Panhandle when it made landfall at 1:00 p.m. CDT on Wednesday. It will also be among the most intense hurricanes to ever have hit the U.S. At landfall, the storm’s 155 mph peak winds ranked fourth highest on record for a hurricane hitting the continental U.S., and the pressure was ranked as the third lowest (the lower the pressure, the stronger the storm), even below what was recorded during Hurricane Andrew in 1992.

Table of the 10 strongest continental U.S. landfalling hurricanes on record, ranked by maximum sustained winds. Source: Philip Klotzbach CSU

This is truly a historic event. As I mentioned yesterday, this storm was only a marginal threat six days ago when it first appeared on some of the long-range model guidance, which illustrates that the scientific community has a lot of work to do in terms of intensity forecasts. In fact, Michael’s rapid deepening, which is defined as less than or equal to a pressure drop of 42 mb in 24 hours, is rare. Only 23 hurricanes in the last 38 years have done this, and Michael was the only hurricane to have this occur right at landfall.

Location of rapidly deepening hurricanes from 1979 – 2017.  Source: Sam Lillo

Hurricane Michael made landfall in Mexico Beach, FL, about 20 miles southeast of Panama City, as a high-end Category 4 hurricane, and I would not be surprised if it was upgraded to a Category 5 when the National Hurricane Center (NHC) conducts its final review of the data.

As the storm crashed ashore, winds gusted to as high as 129 mph along the coast from Panama City to Port St. Joe. The highest storm surge reading that has been observed so far was an inundated level of just over 8.57 feet in Apalachicola, FL – which is the 3rd highest on a new record.  Other areas likely recorded their record highest.

Preliminary wind gust observations from Hurricane Michael. Source:  Here 

Much of the news coverage during landfall was in Panama City Beach, FL. However, the impact at this location was a picnic compared to what occurred just miles east and southeast down the coast where the eye of Michael made landfall. The heaviest damage appears to be in the towns of Callaway, Parker, Springfield, Mexico Beach, Port St. Joe and southeast Panama City, FL. This would suggest that the radius of maximum winds was relatively narrow at landfall (22 miles) and, thankfully, just inland from landfall, Michael tracked over a large sparsely populated area of mostly agricultural land and forest. However, that does not mean that some of the smaller towns or rural households did not see damage. For example, In Donaldsville, GA, which is 82 miles inland from Panama City, FL there was a recorded wind gust of 115 mph that still needs to be verified, but at least a 79 mph gust was reported . Blountstown, FL seems to have been hit particularly hard which is about 40 miles inland. The weather station in Albany, GA recorded a wind gust of 74 mph just before transmission failure occurred.  In fact, to get an idea of where the worst of the damage might be, one just has to look at the lack of surface weather observations due to an absence of site reporting and power outages.

Weather surface observations showing a large gap in observations as a result of very strong wind taking down many of the observations sites. Source: NOAA

 

BMS iVision allows clients to run risks to better understand various impacts from Michael. This is the newest 3 sec wind speed gust in MPH from Verisk Weather Solutions.  There will be some adjustment to this as Verisk Weather Solutions will incorporate surface observations over the next few days for intensity.

There are several reports of weather station anemometers breaking in the high winds, which is why it is possible that wind speeds of greater than 129 mph may have occurred near the landfall location. Given the data that has already been collected, it is plausible that Hurricane Michael will be a design-level event, especially at the immediate coastline and barrier islands along the Florida Panhandle.

Based on an examination of the catastrophe modeling stochastic events that closely match Michael’s landfall location and intensity, insurance industry losses should be in the single-digit billions of dollars. But, as we have seen with past events in Florida, there can be some loss creep, so how high remains uncertain. The big unknown in the modeling at this point is how much property damage occurred in the rural communities inland as Michael tracked into Georgia.

Storm Chaser Accounts
A good gauge of Hurricane Michael’s severity is to get firsthand accounts from the storm chasers who travel the world into the heart of the strongest hurricanes, typhoons and cyclones. Their observations really tell the story of what the hardest hit areas are dealing with in the wake of Michael.
Hurricane storm chaser Josh Morgerman (icyclone) likely has the world record for experiencing the most intense hurricanes all over the world. Those who follow him know he is not prone to exaggeration. Here is his account of the situation in Callaway, FL, via Twitter: “It’s hard to convey in words the scale of the catastrophe in Panama City. The whole city looks like a nuke was dropped on it. I’m literally shocked at the scale of the destruction.”

 


Mark Sudduth, another experienced storm chaser, tweeted similar thoughts: “Drove from Panama City almost to Mexico Beach and I can tell you this is the worst damage from wind that I have ever seen! Absolutely catastrophic! You will not believe your eyes when you see it.”

Michael’s End Game
Hurricane Michael is far from over. Heavy rain and strong winds are still forecasted to sweep through the Carolinas today before exiting the Mid-Atlantic coast Friday morning. Currently 35 miles south southeast of Charlotte, NC, tornado risk is now the biggest threat with local wind gusts capable of bringing down tree limbs.

As we look into next week, we begin to move past this early October period of enhanced Atlantic Basin activity. We can’t entirely rule out new named storm development next week, but, the very good news is that the risk for tropical storms and hurricanes in the Atlantic Ocean is expected to decrease sharply over the coming weeks as a hybrid El Niño winter pattern begins to take hold.

BMS Tropical Update: 10/10/2018 11 AM CDT

Based on the National Hurricane Center’s (NHC) 5:00 a.m. advisory, Hurricane Michael’s pressure had fallen 36 millibars in 25 hours and the wind speed had increased 46 mph over the same timeframe. Having moved into an ideal environment for maximum intensity, with little wind shear, warm water, and a moist air mass with little dry air intrusion, such strengthening was expected, but the extent is still unknown. Michael is currently a Category 4 hurricane with a central pressure of 923, and a maximum wind speed of 150. For a hurricane, Michael is moving fairly quickly to the northeast at 14 mph and is currently 60 miles South Southwest from Panama City, FL.

Given that the hurricane is a few hours from making landfall just southeast of Panama City, FL, the question is, how much more strengthening may occur before landfall? There is a chance that an eyewall replacement cycle could result in a similar or slightly lower intensity, but if an eyewall replacement cycle occurs immediately before landfall, there is a chance that Michael could be an even stronger storm with a larger radius of maximum wind.

Michael arriving as a Category 4 hurricane puts it in a rare group of only four historical Category 4 hurricanes to make landfall during the month of October (Unnamed, Louisiana, Oct. 2, 1893, Unnamed, Georgia, Oct. 2, 1898, King, Florida, Oct. 18, 1950 and Hazel, Carolinas, Oct. 15, 1954). In total, only 28 U.S. landfalls of Category 4-strength storms have occurred since 1850, and there has never been a Category 4 or 5 hurricane to make landfall in the Florida Panhandle. With Michael’s impending landfall as a Category 4 storm, it would be the fourth Category 4 hurricane in just 15 months to hit the U.S. The previous record for the shortest timespan of four Category 4 U.S. landfalls was 1947 – 1950. Needless to say, the long period without a major hurricane making U.S. landfall is starting to correct itself in a big way.

Given the change in the overall intensity forecast, most of the catastrophe model guidance issued yesterday will need to be adjusted upward to account for the stronger storm at landfall, as most guidance issued did not contemplate this scenario. However, there are plenty of stochastic events for comparison, and there should not be an issue of limited matching, like some of the more recent U.S. landfalling hurricanes.

Damage Specifics
I have already touched on the likelihood of massive tree loss in the last few updates, but clearly the increased intensity at landfall confirms that treefall will lead to larger insured losses and will lengthen expected power outages. Unfortunately, this scenario is not handled well in the catastrophe models.

Estimated Poweroutages. In some places it is 100% Source: http://ioe-guikema.engin.umich.edu/Hurricane_Michael.html

Michael’s strength is now at the upper end of what building codes can handle and, while Florida has the best building codes in the country, most structures were built before these codes were enacted, and retrofits have been limited.

While Florida has the best building codes in the state, most structures were built before they were enacted, and retrofits have been limited. Source: David Roueche

 

Wind Swath
Using Verisk Weather Solutions forecasted wind swath allows BMS clients to better understand wind impact to specific risks. Currently, the wind swath suggests a radius of maximum winds to be about 26 miles wide, which is fairly tight for a hurricane. Shortly after landfall, frictional effects rapidly weaken the maximum wind speeds inland. In addition, Tallahassee should be spared any hurricane-force winds, which is a bit of better news, as insured loss will be limited in this large metro area. But, some damage and power outages could still occur.

BMS iVision allows clients to run risks to better understand various impacts from Michael. This is the newest 3 sec wind speed gust in MPH from Verisk Weather Solutions. There will be some adjustment to this swath over the next few days as Verisk Weather Solutions incorporates surface observations.

Storm Surge
There is no doubt that record storm surge will be recorded, as storm surge values of four feet are already showing up in Apalachicola, FL. The next high tide will be just after 6:00 p.m., which should be a few hours after landfall, so, fortunately, Michael is not coming ashore during high tide.
The NHC is suggesting the following storm surge levels:

  • Tyndall Air Force Base, FL to Aucilla River, FL: 9 to 14 feet
  • Okaloosa/Walton County Line, FL to Tyndall Air Force Base, FL: 6 to 9 feet
  • Aucilla River, FL to Cedar Key, FL: 6 to 9 feet
  • Cedar Key, FL to Chassahowitzka, FL: 4 to 6 feet

    Source: NHC

Rural Areas
It appears that, like some of the other devastating Category 4 hurricanes, Michael will also target an area of relatively lower population. However, Panama City has a large amount of exposure and will be the main driver of loss and, like most other U.S. coastal cities, has experienced a tremendous amount of growth over the last 30 years. Most of the other targeted areas inland remain very rural, however.

]Panama City, FL development since 1985.  Source: Walker Ashley

The NHC Cone of Uncertainty overlayed with Census block Household data showing many block areas have less than 600 households.

Here we take the details of the iVision wind swath with the aerial imagery applied to the base map. The radius of maximum winds is forecasted to be about 22 miles at landfall. The strongest winds are forecasted to impact the first 14 miles of coastal exposure as indicated by the first short green line, with the red line indicating areas of higher development. Most of the strongest winds will be over Forest or Agriculture land. Click on image for more detail.

The building codes inland are not as strong as in the coastal areas, such as Panama City, Fl. The older age of the homes inland, coupled with the potential for tree fall, make for uncertain loss estimates. Hurricane Irma illustrated that there are clearly loss creep issues occurring across the state, which will also add to the overall uncertainty around potential losses to the insurance industry.  An early look at some of the catastrophe model guidance suggests a mid to high single-digit billion dollar loss event, but the impacts to Panama City need to be watched closely.

Never Judge a Book By Its Cover
Remember to never judge a hurricane season until it’s over and in the books. This recent uptick in activity is putting the current season back into the “above normal” category, as we now have the development of Tropical Storm Nadine in the East Atlantic, along with Leslie returning to hurricane status on its 19th day of spinning up ACE in the middle of the Atlantic. And, of course, to close out the story, we have a surprise Category 4 hurricane in the Gulf of Mexico. I think that the scientific community needs to provide more accurate seasonal forecasts and move away from the numbers game, which often leads to false impressions of a season. More attention needs to be focused instead on landfall activity. It is no longer acceptable to believe, as the old insurance industry saying goes, that it “only takes one,” since this year there has been two. Hopefully, I made this message clear at the beginning of the season. The good news is that this may be the end game for this season in terms of U.S. landfalls, as a less favorable pattern for new development takes hold across the Atlantic later next week.

BMS Tropical Update: 10/09/2018 11 AM CDT  

Just two years ago we were talking about Hurricane Hermine breaking the 11-year hurricane drought in Florida. With all of the recent U.S. hurricane activity, it’s easy to forget that this drought even occurred, but let’s remember that there are large gaps of the U.S. coastline that have not experienced a major hurricane in a long time. The Panhandle of Florida is one of them, as it has not seen a major hurricane in well over 10 years. For context, iPhones had not yet been released when Hurricane Dennis impacted the Panhandle in 2005. Over this time period, there has also been rapid growth of coastal communities around Destin and Panama City, FL. There are certainly new residents in this area who have never experienced a major hurricane.

Forecasted Track and Intensity
There is good news that Hurricane Michael did not rapidly intensify overnight, and it only showed a small increase in intensity. A fully concentric eyewall has yet to develop, with dry air and wind shear being the likely cause of the lack of rapid intensification overnight. There are some signs that significant strengthening has already began today, as some lightning and deeper convection seem to be initiating eyewall development, and the overall storm seems to be consolidating. Michael is located 360 miles south of Panama City, FL. The current wind speed is 110 mph which is already an increase of 20 mph from the 4 AM NHC Advisory and barometric pressure is 965 mb.

While there is still some uncertainty around Michael’s intensity at the time of landfall, the model track guidance has been accurate since this weekend. The projected path has been targeting an area between Destin and Port St. Joe, FL, with a likely probability (60%) of hurricane-force winds impacting the capital city of Tallahassee.

In the BMS Tropical Update yesterday, I touched on several factors that could lead to Michael’s strengthening and also some that may limit it, such as the lack of a Gulf of Mexico Loop Current and just slightly cooler Sea Surface Temperatures (SST) that Michael will encounter along its track northward. A lot of the intensity questions at landfall will depend on the circumstances over the next 24 hours and whether Michael can intensify enough before making landfall tomorrow afternoon.  Currently it seem to be progressing to major hurricane status later today.

Based on the intensity guidance from an ensemble of models, Michael will at least maintain its current strength until landfall.  Source: www.TropicalTidbits.com

Above is an ensemble of intensity forecasts.  There is agreement that Hurricane Michael will likely be at least a Category 2 storm at landfall, with some of the more reliable hurricane-specific intensity models suggesting that strengthening will occur right up until landfall, which is an important point. Some models suggest an even stronger storm which needs to be watched. Currently, the NHC forecast is still suggesting the wind speed at the time of landfall is expected to be 126 mph, with higher 3 second gusts possible. The overall size of the storm, which is sometimes referred to as the RMAX, is a bit unknown at this time, as eye wall replacement cyclones and the overall intensity of the storm will determine this over the next 24 hours. The forward motion of the storm at landfall appears to be relatively fast (16 mph), which could extend damage further inland as the storm weakens. These stronger inland winds will likely cause power failures and downed trees over a large area. Wind gusts of 70 mph are likely over southwestern Georgia.

Wind Risk
Using Verisk Weather Solutions forecasted wind swath allows BMS clients to better understand wind impacts to specific risks. This high-resolution model wind field shows hurricane-force winds rapidly weakening inland due to a frictional effect, which is important when determining the overall damage estimation to inland risks.

BMS iVision allows clients to run risks to better understand various impacts from Michael. This is the newest 3 sec wind speed gust in MPH from Verisk Weather Solutions. There will be some adjustment to this forecast over the next few days in both track and intensity.

However, this predicted weakening of winds inland does not mean that the winds won’t be strong enough to knock down some trees. As mentioned in yesterday’s update, the tree cover in the Florida Panhandle, particularly from Apalachicola up to Tallahassee, is dense. This is why much weaker Hurricane Hermine caused such extended power outages that lasted weeks in some locations. It does not take a major hurricane to cause significant wind impact in the Florida Panhandle – the peak wind gust reported in Tallahassee from Hurricane Hermine was only 64 mph. Clearly Michael’s degree of disruption will be several times worse in terms of power outages when it comes ashore. With all of the foliage and the lack of major hurricane activity over the last 10 years, a natural culling of weak and damaged trees and branches can be expected. And, of course, even tropical storm-force winds can cause minor damage to structures. This could complicate the overall loss estimate from the modeling companies, although they do try to take into account tree density around individual risks.

Above ground biomas thickness (Trees). The darkest greens indicate areas with the densest, tallest, and most-robust forest growth (Grieser et al., 2011)

Source: Estimated Poweroutages. In some places it is 100% http://ioe-guikema.engin.umich.edu/Hurricane_Michael.html

 

Tornado Risk
An often overlooked aspect of a landfalling hurricane is the tornado threat. I made several mentions to this prior to Florence making landfall, which resulted in over 40 confirmed tornadoes. I would also expect several dozen tornadoes to occur with Michael as it comes ashore and races across the southeastern states.

Storm Surge Risk

Likely one of the biggest stories from Hurricane Michael will be the storm surge.  I am sure some storm surge records will be broken. The Florida Panhandle is very susceptible to this, but the extent of the surge will depend on the overall track and intensity of the storm. To illustrate, Dr. Risk Luettich at University of North Carolina Chapel Hill ran a few simulations along the NHC cone of uncertainty which shows that the exact track of Hurricane Michael will determine the storm surge, estimated to be as high as 12 feet if the worst case scenario develops between Indian Pass, FL and Ceder Key, FL.

The best tool for estimating storm surge is the NHC storm surge inundation product, which provides a detailed look at the water level that is expected above the ground. The catastrophe models have a good handle on the various storm surge scenarios that are possible based on the track and intensity.


Early Insured Loss Estimates
Today the catastrophe modeling companies will continue to zero in on stochastic model event selection. Based on the historical catalog, there are plenty of comparable events for the companies to use for loss analysis. As pointed out, there are some unknown variables that are a bit harder to model, such as tree fall and power outages. Florida has some of the best building codes in the country, however the standards in the Panhandle are not as high as southern Florida. This will be key along with the construction quality over more interior parts of the panhandle and Southern Georgia. However, the degree of damage from lower wind speeds is often overlooked for older wood frame building which are common in the region.

Just one sample of Probability of Damage from a 2 story wood-frame.

Overall, insured loss from wind and storm surge from the historical and modeled stochastic events appear to have a range between $1B and $3.5B. The actual loss will depend highly on the parameters and location of landfall. If the storm tracks to the east side of the NHC cone of uncertainty, which is a rural area, damage should be lower, but tracking too far to the east will increase inland loss in Tallahassee.

BMS Tropical Update 10/08/2018 10 AM CDT

Twenty-one days ago, I made mention that the Atlantic Hurricane Season was not done yet and, overall, the tropical troubles in the Atlantic Ocean would be shutting down for a few weeks. This has been the case for the most part, with very few of the named storms since Florence resulting in any meaningful ACE (Accumulated Cyclone Energy). Really, named storm Leslie has been the only system to have had any significant ACE accumulate in the North Atlantic. However, all of that is about to change. I previously made mention that the next burst of upward motion would be back over the Atlantic during the first week of October and, like clockwork, on October 2 the National Hurricane Center (NHC) began monitoring a broad area of low pressure that had developed over the southwestern Caribbean Sea. After taking most of last week to get organized, this system is now known as Hurricane Michael and is currently located 50 miles south of the western tip of Cuba.

Above is the NHC reasonable arrival of tropical storm force winds as of  NHC advisory number 7.

Michael has already caused significant flooding across Central America with at least nine fatalities across several countries. Unfortunately, the forecast suggests that more damage is expected over the next few days as Michael moves north over the warm waters of the Western Caribbean. In fact, these warm waters will be key to Michael’s final intensity at landfall as it tracks toward the Big Bend area along the Florida Gulf Coast.

Storm Fuel
Sea surface temperatures (SSTs) are average to slightly below-average, (29°-30° C or 84°-86° F) in the Western Caribbean and Eastern Gulf, but it is still plenty of  fuel to feed Michael as it heads northward.

Above is the SST analysis from www.TropicalTidbits.com showing the water temperatures are plenty warm along Michael’s track northward to allow for strengthening.

Another factor that might be at play in terms of potential fuel for Michael as it tracks north is how much it will churn up deep, colder water, which might put the brakes on any major rapid intensification. But, when unusually warm ocean waters extend to depths 100 meters or more below the surface, the hurricane’s winds simply stir up more warm water and allow dangerous and rapid intensification to occur if wind shear is low.

The plot above is the depth of the 26 degree isotherm (78.8 F). Currently where Michael is located the depth of this warm water is over 100 meters (328 ft). The good news is the old loop current is to the west of Michael’s projected track so the warm water is not as deep along its track northward. Source: NOAA

Michael will be tracking right over the deepest warm water, which is often referred to as the Loop Current — an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and then goes west of the Bahamas as the Gulf Stream Current. Often, the Loop Current bulges into the northern Gulf of Mexico and sometimes will shed a clockwise rotating ring of warm water that separates from the main current. When this occurs, it can add even more fuel to passing storms.

The Loop Current flows northward into the Gulf of Mexico. Every 6 – 11 months, a bulge in the current cuts off into a clockwise-rotating eddy that then drifts slowly west-southwestward toward Texas.  Source: NOAA

The good news is that it appears Michael will pass to the east of the last Loop Current eddy, which will limit some fuel for Michael as it tracks northward. But, this doesn’t mean that Michael won’t reach Category 3. It just indicates that the top-end intensity will be limited, as was observed with Katrina or even Harvey last year, which was fueled by an old Loop Current eddy.
The other factor to consider that may limit intensity is the westerly shear near the storm as it tracks northward toward the Florida Big Bend Gulf Coast. However, despite 30 knots of wind shear, Michael has still managed to strengthen over the last 24 hours and has already had an impressive 982 mb central pressure. If wind shear weakens, Michael could continue to strengthen and potentially make landfall as a weak Category 3 hurricane.

Based on the intensity guidance from an ensemble of models, Michael will strengthen until landfall. In fact, the there is a 36% chance of achieving major hurricane intensity in the next 24 hours. Source:  www.TropicalTidbits.com

No Stranger To Named Storm Activity

Historical hurricane tracks within 65 mile radius centered just south of Tallahassee, FL with a filter applied to show 11 category 2 and 3 hurricanes have made landfall in the area since 1850.

The Florida Panhandle has been no stranger to hurricane activity over the last three years.  In fact, since 1850, 11 category 2 and 3 hurricanes have made landfall in the location under watch from Michael.  The most recent being Hurricane Kate 1985 which today would result in close to one billion of industry loss.  Subtropical Storm Alberto and Tropical Storm Gordon have already caused $168M of loss this year to the insurance industry to in the Gulf Coast States. The often forgotten Hurricane Nate in last year’s busy U.S. landfall season impacted the same general area with similar insured loss.  In 2016, just over $200M in insured losses resulted from Tropical Storm Colin and Hurricane Hermine, which, as mentioned, might be the best overall analog for the industry at this time. In Florida, Hermine’s impact was enhanced by the natural bend in the coastline and abnormally high tides, with heavy precipitation along the Gulf Coast causing significant damage. In Citrus County, FL, one of the worst affected areas, 2,694 homes were damaged, of which 531 experienced severe damage. If you recall, the Big Bend area has a high tree density which, during Hermine, resulted in large number of power outages that stretched for weeks in locations all the way to the Tallahassee area, which was hit particularly hard with tree fall.

Michael’s impacts could be multiplied here since it is expected to be a major hurricane at landfall. The current model guidance suggests a landfall location between Miramar Beach to Apalachicola, FL, with the American GFS model suggesting a faster storm making landfall on Wednesday afternoon, while the European ECMWF model is predicting Thursday morning. However, regardless of timing, the insurance industry impact could be significant. The U.S. coastline between Indian Pass to Crystal River is one of the most vulnerable locations to storm surge. The current forecast suggests up to 11 feet of storm surge in this area, which could go even higher as Michael intensifies so don’t be surprised if values above 11 feet start to show up in the forecast.

Unlike Florence, Michael will not linger and will move rapidly to the northeast across Central Georgia and southern South Carolina. There will be a swath of 4-8 inches of heavy rain just along and to the northwest of the center of the storm.
With a delayed autumn, all the leaves are still on the trees across a large portion of the southeast, which will exacerbate power outages. The highest wind gusts are expected along the coast from Destin, FL to Tayler and Wakulla counties and, as with Hermine, strong winds will have a big impact all the way into Tallahassee, which has the largest population area of the locations under threat, with the rest of the coastline being fairly rural.

BMS iVision allows clients to run risks to better understand various impacts from Michael. This is the newest 3 sec wind speed gust in MPH from Verisk Weather Solutions. There will be some adjustment to this forecast over the next few days in both track and intensity.

BMS Tropical Update 9/17/2018 12 PM CDT

Florence Event Summary

Tropical Depression Florence is now transitioning to a non-tropical weather system, but it‘s still dumping rainfall over North Carolina and Virginia. As the historic rains and flooding slowly ease up along the North Carolina coast and the population is gradually let back into their communities, the insurance industry will now begin to get a better sense of the damage. It should be noted, however, that travel in this general area is still very limited, and it could be days before the first notice of loss is provided for some risks.

The National Geodetic Survey (NGS) has provided its first post-event aerial imagery, which can be found here. They still have yet to fly over the hardest hit areas, but it’s expected that these images will be added over the coming days. Other high resolution images can be found here.

For many, the weekend winds were not the problem as Florence moved slowly across the Carolinas. At this  link provides some of the official top wind gusts observed across the multi-state region.  The top observed wind speed was 112 mph gust from a Buoy 30 miles south east of  Topsail, NC.  Onshore the highest wind gust continues to be 105 mph as observed at Wilmington Int’l. Airport.

The wind gusts, however, may only be half of the problem as the long duration of strong winds will likely increase insured losses. A low level wind event of long duration can inflict just as much damage as a shorter and stronger wind gust event. Another thing to consider is that many of our building design codes and vulnerabilities built into the catastrophe models are developed around the gust. This will result in a bit of uncertainty around the loss estimates within the catastrophe models.

Above is a look at the overall event summary of the wind duration in hours of wind gusts of 50+ mph. This is provided by Verisk Weather Solutions and available in BMS iVision.

Broken Rainfall Records
Unfortunately, the rainfall forecast has played out as expected. Numerous locations in southeastern North Carolina have endured more than 20 inches of rain, with Onslow and Carteret counties being hit particularly hard. At least twelve locations appear to have broken the state record for tropical storm or hurricane rainfall, exceeding the 24.09 inches that fell near Wilmington during Hurricane Floyd in 1999.

Here is the selected preliminary storm total rainfall in inches from 2:00 p.m. EDT, Thursday, Sept. 13 to 10:00 a.m. EDT, Monday, Sept. 17. It should be noted that the Elizabethtown, NC total of 35.93 inches is the most for any tropical storm or hurricane along the East Coast north of Florida, and this represents a new 2-day and 3-day rainfall record for North Carolina. However, it does not appear at this time that the 24-hour rainfall record for the state was broken. It’s still likely that higher observation totals could result, as reports are still rolling in. It wouldn’t surprise me to see a total value of around 36 inches eventually being reported. Further south, the town of Loris, SC posted a preliminary total of 23.63 inches, which is a new rainfall record from a tropical system in South Carolina.

Above is a look at the overall rainfall event summary which shows a large area of rainfall values of 12+ inches. This is provided by Verisk Weather Solutions and available in BMS iVision

The river water is starting to recede in some areas, but some areas could see the water level continue to rise as the water moves toward the coast. For example, the Cape Fear River in Fayetteville, NC is already at flood stage and is forecasted to rise to 62.3 feet by Tuesday morning.  Water levels along the Lambert River are also expected to rise.

River level information can be found at the National Weather Service site here. Some online maps, such as Google Maps, the NC DOT, provide road closure information which helps to illustrate the areas that are experiencing high water.

Insured loss
The National Flood Insurance Program (NFIP) will bear the lion’s share of losses, and it’s apparent that a large protection gap exists with the very low NFIP take-up rate that we have previously mentioned. It’s still unclear if this level of flooding will have an impact on the catastrophe bond and reinsurance programs that help the NFIP with recoveries. The various insured loss estimates that have been publicly released from the modeling companies range from $2.5 billion to $5 billion in insured loss.

What Tropical Troubles Are Next?

I mentioned several times last week that, overall, the tropical troubles in the Atlantic Ocean would be shutting down this week. In fact, today is the first day since August 31 that the Atlantic Basin is not generating ACE (Accumulated Cyclone Energy), which means the basin should have a few quiet weeks ahead. The only area of concern for the insurance industry at this time is the remnants of Isaac, which are located just south of Jamaica. Overall, the chances for formation are very low as the system moves toward the Yucatan Peninsula.    Tropical Depression Joyce in the far eastern Atlantic continues to lose organization and should dissipate in a few days.

Although the Atlantic will be quiet for the next few weeks, I don’t think the season is done quite yet. A burst of upward motion could come back into the tropical Atlantic during the first week of October. This would correspond climatologically with typical development originating in the western Caribbean Sea this time of year instead of coming off the coast of Africa.

The figure above shows the named storm points of tropical cyclone genesis from October 1 – 10 between 1851 – 2015. Focus will now shift closer to the U.S. and western Caribbean.

BMS Tropical Update 9/14/2018 12 PM CDT

The content below is the same as what was sent in the e-mail.

According to the National Hurricane Center, at 7:15 a.m. EDT today, Hurricane Florence made landfall at Wrightsville Beach, NC, just east of Wilmington, NC, the largest city in the area with a population of just over 117,000. Florence came ashore with winds of 90 mph and a central pressure of 958 MB. However, as many in the media have communicated, the storm surge impacts are likely to be similar to a major hurricane at landfall.

Wind Observations
Many areas along the coastline have experienced tropical storm-force winds for over 24 hours now, and by the time Florence moves inland, some areas will have had well over 24 hours of hurricane-force winds. There are numerous reports of wind gusts over 80 mph and a handful over 90 mph. The highest wind gust I have seen reported is 105 mph at the Wilmington, NC airport, which is the second-strongest wind measured at that location in 60 years. The strongest ever recorded was 135 mph during Hurricane Helene in 1958. It should be noted that there could be even higher wind gusts, as all observations at this point are preliminary.

Below is the BMS iVision wind swath provided by Verisk Weather Solutions, which shows the extent of the three-second wind gusts along the coast and how far inland hurricane-force gusts could be observed.

BMS iVision additionally has other severe storm attributes, such as rainfall and wind duration over 50 mph.

At this point, according to poweroutage.us,  there are approximately 575,00 power outages reported across North Carolina and South Carolina with the number growing each hour.

Tornadoes
So far, the Storm Prediction Center has only received one report of a tornado. However, as Florence tracks inland, it is expected that tornadoes will become increasingly likely today in the northeastern part of the hurricane. A tornado watch remains in effect for portions of eastern North Carolina.

Surge Observations
Storm surge was expected to be a major problem along coastal areas, as Florence’s slow motion and overall large size allowed for the constant piling up of water along coastal and inland waterways. Although observations of storm surge are preliminary, reports of six feet have been observed in New Bern, NC, which is 30 miles inland along the Neuse River. If the observations are correct, this is approximately two feet higher than the observation during Hurricane Irene in 2011, according to the National Weather Service in Morehead City. Observations of storm surge along the coastal section could be higher, as observations are limited at this time. However, since the worst of Florence came ashore as the overnight high tide was receding, overall maximum water heights may have been reduced.

Rainfall
The rainfall story continues to evolve with the highest observation coming from Atlantic Beach, NC, where 30.68 inches of rain have been witnessed over the last 24 hours. If validated, this would wipe out the previous state 24-hour rainfall record. However, some reports suggest this reading could be in error. There have been other reports of 12-18 inches in the last 24 hours, and this will undoubtedly create localized flooding issues. Since the storm just made landfall, expect much higher amounts by the time Florence finally moves inland, which might not be until Sunday morning.
https://nc.water.usgs.gov/realtime/rainfall.php

Insured losses
Overall damage seems to be aligned with the wind speeds that have occurred, such as the occasional gas station awning being damaged, and siding and asphalt shingles being torn off residential structures. The damage could be higher than normal due to the long duration of hurricane-force winds. Along the coastal barrier islands, many structures have first floor flooding. But, keep in mind, many of the coastal structures are designed to flood and are typically only temporary living spaces or used for storage. Thankfully, the overall insured loss estimates are many times less than what was predicted earlier this week. Only a few catastrophe modeling companies have publicly provided loss estimates at this time, which range from $2B to $5B for wind and surge. It should be noted, however, that any loss estimates provided are preliminary, and the insurance industry is accustomed to loss estimates creeping up over time.

Looking Ahead for Tropical Troubles
Florence will slowly track westward into eastern Tennessee by Sunday night. By Monday morning, Florence is expected to be caught up in a trough of low pressure and should quickly move across the Northeast states during the middle of next week, resulting in a swath of 2 to 4 inches of rain along the Appalachian Mountains.

Isaac is currently a tropical depression and will likely be reclassified as an open wave. Currently, there is a 25% probability that Isaac comes back to life over Cuba, and if this occurs, it could have an influence on Florida or the Gulf Coast states later next week.

Overall, there has been a fair amount of activity lately. Keep in mind, however, that we are still four days from the actual peak of the hurricane season. It is all downhill from here. As I mentioned at the start of the week, the tropical Atlantic should begin to shut down any new activity in the coming days, but any activity that has already developed will need to be watched closely. The next expected uptick in activity should be the first or second week of October.

BMS Tropical Update 9/13/2018 12 PM CDT

The End Game
After tracking over 3,292 miles across the Atlantic Ocean, Florence will become one of only two hurricanes to make U.S. landfall from its origination point off the coast of Africa since 1851.  It also becomes the only hurricane since 1851 to make landfall from its location that was observed in the middle of the Atlantic Ocean back on September 6th. For the last 2-3 days, the landfall target has been focused on an area between Myrtle Beach, NC and Morehead City, NC, with the primary area of impact being just north of Wilmington, NC in New Hanover, Pender and Onslow counties.

With Florence’s center core finally showing up in the long range radar, it would appear the end game is finally near. The biggest change in the forecast since the start of the week has been the change in intensity, which is a known issue in hurricane forecasting. There has been some general improvement in skill over the last decade, but more recently over the last five years, intensity forecasting has been challenging.

Annual average official intensity errors for Atlantic basin tropical cyclones for the period 1990-2017, with least-squares trend lines superimposed. Source NHC

As Florence begins to move over the warm waters of the Gulf Stream, will it regain strength? This is unlikely, as the core of the hurricane is finally falling apart due to multiple eyewall replacement cycles, along with dry air and wind shear that have been finishing the job over the last 24 hours. However, because Florence is moving over the warm waters of the Gulf Stream and wind shear is a bit more relaxed, it’s likely that only gradual weakening will occur until its landfall around 3:00 a.m. EDT tomorrow. Shortly after this expected landfall, a more rapid pace of weakening is expected as the center of the storm moves inland into central South Carolina.

Storm Surge Impacts
Hurricane Ike made landfall on the Texas coast 10 years ago this morning. It was only a strong Category 2 hurricane at landfall, but don’t make the same mistake by judging Florence as only a Category 2 hurricane, as disastrous rainfall flooding and storm surge impacts are likely to occur. Based on the NHC storm surge inundation forecast, the storm surge is expected to be between 9 and 13 feet from Cape Fear to Cape Lookout, NC, where the natural concave shape of the coastline will enhance the surge. It appears that the surge will come ashore just after high tide tomorrow, which occurs around 11:30 p.m. tonight with low tide occurring at 5:00 a.m. tomorrow.

A great resource to use to understand storm surge risk is the very detailed NHC Storm Surge Inundation maps. 

High Impact Rainfall

Disastrous flooding is expected over wide areas, with the heaviest rainfall amounts coming near the coastal Carolinas. The Central Appalachians could also experience heavy rain over mountainous terrain, and orographic lifting rain will likely trigger mud and rockslides. It still appears likely that the North Carolina state record for rainfall from a named storm – 24.06 inches from Hurricane Floyd in 1999 – will be broken, but it’s unlikely that the greatest 24-hour rainfall record of 22.22 inches will be broken. Because Florence will slow its forward motion after landfall, the large amount of rainfall is a big concern as it all flows to the Atlantic Ocean. The constant onshore flow over the next two days could back up some of the water trying to escape from the inland tributaries.

NOAA Forecasted Rainfall over the next 7 days. Source NOAA

The National Flood Insurance Plan (NFIP) Take-Up Rate in the Carolinas as a percentage of county housing units is less than 1% for many inland counties, with much of the NFIP risk located at the coastal counties. Even the take-up rates in the highest storm surge impact counties of New Hanover, Pender and Onslow counties is relatively low , illustrating the large protection gap that exists across the Carolinas.

NFIP take-up rates as a percent of county house units. Source Mark Bove Munich Re

Wind Impacts
Tropical storm-force winds (39-plus mph) are expected to arrive in the hurricane warning area by early this afternoon. Hurricane-force winds (74-plus mph) may arrive by this evening. Even though Florence is expected to be much weaker than initially thought, it does not mean that wind damage won’t occur. Numerous downed trees and long-lasting power outages could occur near where Florence’s center strikes and even further inland. Both Hurricane Ike 2008 and Hurricane Sandy 2012 were large hurricanes in size and had a wide range of impacts.

Another thing to watch with Florence is the relatively slower movement once it makes landfall. Hurricane damage is often associated with peak wind speed. However, an AIR-Worldwide Blog by Dr. Vineet Jain in 2010 suggests that claims data and post-disaster survey findings repeatedly and consistently show that the amount of damage a structure experiences is also a result of wind duration—how long a hurricane’s winds batter a structure. In the end, neither peak wind speed nor wind duration are a favorable scenario for a structure’s ability to endure damage above various design code levels. The cumulative stress load variations from long term exposure to hurricane winds can increase the overall damage potential to a structure beyond just the peak gust endured at a location. However, keep in mind that Category 2 Hurricane Arthur that hit the Outer Banks in 2014 did not register as a Property Claim Services catastrophe event, illustrating how building codes are working and how resilient structures are becoming along the coastline of North Carolina.

Caption: AIR’s analysis of detailed claims data demonstrates the effect of wind speed duration on building damage ratios. Source AIR-Worldwide

 

BMS iVision allows clients to run risks to better understand various impacts from Florence. This is the newest 3 sec wind speed gust in MPH from Verisk Weather Solutions. Notice the expanding wind swath with the 90 mph wind gust swath extending out 60 miles from the center of the storm.

Tornado Impacts
Yesterday I bought up the risk of tornadoes from landfalling named storms. After doing a bit more research, it seems that the tornado threat from Florence in the Carolinas might be higher than we’re normally accustomed to seeing with landfalling named storms. Florence’s larger and more intense wind field increases low-level shear over a larger area, favoring more tornadoes. See McCaul (1991). Clearly this could add another element to the landfall threat associated with Hurricane Florence and tornado watches are posted.

Power Outages
Given the potential amount of rainfall and tropical storm force-winds that could reach areas well inland, the insurance industry should expect high amounts of tree fall that will produce power outages. The Guikema Research Group at the University of Michigan has now produced power outage maps. As the storm makes landfall, www.poweroutage.us will be a good resource for real-time power outages.

Quiet Time Ahead
Keep eyes on Isaac which will likely be reclassified as an open wave, but some models still bring it into the Gulf of Mexico later next week as a named storm.

Overall there has been a fair amount of activity lately, but keep in mind that we are two days off the peak of the hurricane season and it is all downhill from here. As I mentioned at the start of the week, the tropical Atlantic should begin to shut down any new activity in the coming days, but any activity that has already developed will still need to be watched closely. The next expected uptick in activity should be the first or second week of October.