partner login

BMS News

BMS Tropical Update – Mid-August

It has been 45 days since I last provided a tropical update, mostly because there has been little to write about in term of U.S threats. However, with the peak of the season approaching, I would like to provide an assessment of the seasonal outlook that was outlined at the start of .the season. I will also provide some initial thoughts on a threat to the Texas coastline with remnants of Harvey expecting to come back to life over the next 24 hours.

Harvey’s Return

My general philosophy for posting tropical updates on specific tropical systems is to not post anything until there is a real concern of a U.S. landfall and subsequent impact to the insurance industry. I think we have now reached that threshold with the system formerly known as tropical storm Harvey, which is now located over the Yucatan Peninsula. It is expected that this system will be reclassified as a tropical storm Harvey as strengthening is expected during the next couple days, and it could even reach hurricane status as it approaches the U.S coastline by the end of this week. I expect the NHC to start issuing watches and warnings for the Texas coastline within the next 24 hours.

Harvey is currently forecast to make landfall somewhere between the Texas / Mexico border and central Louisiana, so there is obvious uncertainty with the forecast track guidance until Harvey moves back into the Bay of Campeche and reconnaissance flights get a better idea of where the exact center of the system is. The computer models don’t have the best read on this weak system at this time.

Current Track Ensemble Guidance for Harvey

Currently most of the model intensity guidance keeps Harvey as a strong tropical storm until it approaches the Texas coastline. However, systems that enter the southern Gulf of Mexico can strengthen rapidly and likely will do so until they make landfall. The water temperatures in the southern Gulf of Mexico are some of the warmest in the world and this means there is plenty of fuel for Harvey to strengthen rapidly and become a hurricane at landfall, which cannot be ruled out at this point. The further north the storm tracks up the Texas coastline, the longer the opportunity for the storm to stay over warm water and become stronger. This needs to be watched carefully.

The tropical cyclone heat potential, is a measure of the integrated vertical temperature between the sea surface temperature and the estimate of the depth of the 26°C isotherm. These regions have been associated with the sudden intensification of tropical cyclones.

Regardless of Harvery’s ultimate strength and track, it almost certainly looks like Harvey will have a slow forward motion and dump as much as 8” – 12″  of rain along the Texas coastline over the next week and if it stalls out like some models forecast the amount of rain could be even higher.  This will likely cause areas of flooding and past rainfall of this amount in the Houston area have not been good.

Current NWS Accumulated Rainfall over the next 7 days.

Peak of the Season Approaching
Several tropical systems have been monitored for formation by the NHC since my last update, of which five of them have been officially tracked. As I stated in my last update, tropical systems moving off the coast of Africa in the Main Development Region (MDR) will struggle to develop, but the overall environment becomes much better for development once those system get closer to the U.S. mainland. So far this season we have seen very little development in the MDR. This is mostly due to dry dusty air that has been a common deterrent the last few seasons. It’s not impossible for a named storm to develop off the coast of Africa, but the environmental conditions are limiting the opportunities this season.

The development that we have seen has come in waves this season, and without the major influence of an El Niño or La Niña as mentioned in the July 7 update, the MJO would likely influence these waves of named storm activity. I mentioned “The next phase of the MJO which could possibly enhance Atlantic named storm activity would occur near the end of July or first part of the August.” Five systems have been tracked by the NHC during this period, with Gert actually reaching category 2 hurricane status as it moved away from the east coast of the U.S. However, most of this year’s tropical systems have been weak and short lived with no major hurricane yet in the Atlantic basin. The Accumulated Cyclone Energy (ACE) is running about 84% of normal for the year, with almost half coming from Hurricane Gert. However, we have already reached the letter H in regards to named storms. This typically wouldn’t occur until around September 24, so we are far ahead of normal in regards to named storm count, which is in line with many of the seasonal forecasts.

 

Typically the Atlantic basin would be coming alive with activity with the peak of the season approaching on September 10, but the MJO’s expected move into a negative phase over the Atlantic Basin should suppress tropical convection and make it more difficult for named storm development during the peak of this season. Although named storm formation could still occur over this period, environmental factors such as dust and the MJO are pointing to less activity than normal for the month of September.

Currently the Red Area is Suppressed. This means less activity. The Pink and Blue is Active Phase of the MJO which can enhance convection and named storm activity. The three week forecast suggest this suppressed phase will move over the Atlantic during the peak of the Atlantic Season.

With the understanding that the North American weather pattern could change over the next month or so, we have seen two distinct tracks take shape this tropical season. One of these tracks is for tropical waves to take a southern route across the Southern Caribbean and influence the Yucatan, similar to Franklin and the current path of Harvey. The other path is for storms to track north of the Leeward Islands and influence Florida and the east coast. We have seen a few tropical waves influence south Florida (currently Invest 92L being watched by the NHC) and of course Gret strengthened along the east coast. This follows the general thinking for the season that as tropical waves move off Africa, they won’t strengthen into named storms until they are close to the U.S.

Without a major North American pattern change and implementing the ideas of clustering which is built into catastrophic risk models, it appears likely that we will see tropical waves take similar paths yet this year. However, as we approach the end of September and into October, which is when the next positive phase of the MJO would likely move back over the Atlantic, the current North American weather pattern will likely change.

Although our named storm count is high, overall ACE for the season so far is below normal. However, on the 25th Anniversary of Hurricane Andrew’s formation, it may be worth the reminder that it only takes one storm to have a major insured impact.

BMS Tropical Update 8/23/2016 12 PM CDT

It’s time for U.S. insurers to take careful note of tropical wave 99L that I blogged about on Friday. This tropical wave is currently 400 miles to the east-southeast of the Leeward Islands. At its current translation speed of 15-20 mph, the wave will reach the eastern Caribbean tomorrow morning and Puerto Rico on Thursday. A hurricane hunter is slated to investigate 99L this morning, and the data it collects could suggest a high likelihood that the tropical wave will develop into a named storm: the name “Hermine” awaits. This hurricane hunter data will also provide improved data for numerical weather models and will augment future track forecasts.

Aug2312PM_AtlanticImage
Future Possible Track
Climatology suggests Invest 99L is at least six days away from any U.S. interaction, so a great deal of uncertainty still exists within the forecast. However, based on its current location, climatology suggests with 32% probability that a named storm will impact the U.S. and with 27% probability that a named storm will make U.S. landfall.
When you factor in forecast-model suggestions, these probabilities increase: model consensus indicates that Invest 99L will track toward the Northern Caribbean islands. Some divergence starts to occur at this point within the models: Some of the models take the system into south Florida and some take the system into the Bahamas. But either scenario increases the probability that the system will track toward the U.S. over the next few days.

Aug2312PM_99LForecastedTracks

 

Despite forecast uncertainty, many scenarios have potential to play out in the next six days. One historical marker looms large. On this date in 2005, Tropical Depression 12 formed in the Bahamas and was forecasted to track toward Florida as a tropical storm. A few days later, Tropical Depression 12 developed into Katrina and hit south Florida. It was the last August hurricane to make landfall in Florida. We now know Katrina quickly gained strength in the Gulf of Mexico to become one of the most devastating hurricanes in U.S. history. It should also be noted 24 years go today hurricane Andrew made landfall in south Florida after rapidly strengthening near the Bahamas.  Just as was experienced with  hurricane JOAQUIN storms can rapidly strengthen in this general area given the very warm sea surface temperatures.

01_AL1205W

TD 12 forecast on this date in 2005. TD 12 went on to be hurricane Katrina.

Katrina, Andrew, Joaquin serve as a reminder that hurricanes can develop rapidly in the right conditions and forecast tracks have uncertainty five to six days out. In the more than 10 years since Katrina, weather models have improved, and they suggest tropical troubles could be brewing closer to the U.S. later this weekend. These 11 years since Katrina have also brought new and untested insurance companies and 2 million additional Florida residents, many of whom have never experienced a hurricane. All of these facts add up to the conclusion that Invest 99L requires careful watch over the next several days.

Other Systems:

Fiona – continues to weaken south of Bermuda and is no longer being watched by the National Hurricane Center.  It maybe come back to life so stay tuned, but stay out to sea.

Gaston – should become a hurricane later today and track into the central Atlantic and east of Bermuda early next week.

2014 Atlantic Hurricane Season and an El Niño

When the 2014 hurricane season officially starts on June 1, it will have been 3,142 days since the last Category 3 hurricane made landfall along the U.S coastline (Hurricane Wilma, 2005). This shatters the old record for the longest stretch between U.S. intense hurricanes since 1900. In fact, landfalls in general have been down since 2005, with a rate of 0.75 landfalls occurring per year since 2006, versus the rate of 1.78 that had been experienced since the warming of the Atlantic Multidecadal Oscillation in 1995.

Although Superstorm Sandy is still fresh in the minds of many insurers in the Northeast, insurers in hurricane-prone states could become complacent due to the lack of storms since 2005. The “doom and gloom” forecasts for the 2013 hurricane season failed to materialize, and early predictions for 2014 have already hinted at below-normal named storm activity, contributing to such complacency. These Atlantic hurricane forecasts call for hostile conditions across the deep tropics due to the development of an El Niño, which brings increased wind shear across the Main Development Region (MDR) of the Atlantic and could lead to less overall named storm formation.

There is a lot of chatter about the possible development of a “super El Niño” similar to that which occurred in 1997–1998. This type of event would drastically limit overall hurricane development. However, the Pacific Ocean is in an overall cold phase (the Pacific Decadal Oscillation (PDO)), a state which often makes it difficult to have strong, long-lived El Niño events. Instead, the PDO suggests a short-lived El Niño, but the specific manifestations of any given El Niño event greatly depend on its strength. Every El Niño event is different, but overall the phenomenon has become associated with the following:

* An uptick in the average global temperature

* Increased rainfall in Peru

* Drought in Australia

* Warmer than average temperatures in Alaska

* Elevated rainfall in California during moderate and strong events

* Dry weather in the Pacific Northwest states

* Increased snowfall in the Mid-Atlantic, especially for moderate El Niño events

* Cooler and wetter than average conditions in the Southeast U.S.

* Increased hurricane activity in the eastern tropical Pacific basin

* Depressed hurricane activity in the tropical Atlantic

While El Niño years generally have lower instances of named storms that make landfall, there are plenty of examples of El Niño-influenced hurricane seasons that have impacted the U.S. coast. Below is a look at such years, as well as the number of storms that made landfall and the adjusted insured loss in 2014 dollars.

Year # of Landfalling Storms Adjusted 2014 Insurance Loss
1957 2 $1,489,000,000
1965 2 $11,177,500,000
1969 1 (Camille) $8,250,000,000
1976 5 $300,000,000
1991 1 (Bob) $1,730,000,000
1992 1 (Andrew) $28,005,000,000
2002 6 $902,050,000
2004 6 $28,387,500,000

As we learned last year, seasonal forecasting has its challenges. Currently, there is a 75% chance of an El Niño developing this summer during the peak of the Atlantic hurricane season. However, in 2012 when an El Niño watch was issued, an El Niño never formed. In fact, since 1997 there have been five threats of a super El Niño that never developed. Therefore, taking into account the uncertainty in any seasonal climate forecast and the history as shown in the chart above, there can be an increased threat from tropical storms even in El Niño years. The 2014 seasonal forecast might also focus on other regional climate forces. One of these forces might be that the Sea Surface Temperatures (SST) off of the Eastern Seaboard of the U.S. are warmer than normal, which not only adds fuel to storms like Superstorm Sandy, but also could lead to deepening of pressures if any tropical disturbances tap into this potential fuel source later this summer. This warmer water also likely means that storms could develop closer to the U.S. coastline.

The new seasonal hurricane forecasts, which will roll out around June 1, tend to have increased accuracy as compared to the spring projections. These forecasts will continue to reflect the evolution of the El Niño, which can be followed on the Climate Prediction Center’s website (El Niño/La Niña Current Conditions and Expert Discussions). BMS will also provide updates throughout the season, but expect new seasonal forecasts to call for named storm formation to be below normal for the 2014 Atlantic hurricane season.