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BMS Tropical Update 9/14/2016 12 PM CDT

I think everyone was surprised to the naming of  Tropical Storm (TS) Julia overland last night at 10 PM EDT. My jaw basically dropped when my iPhone alerted me that the National Hurricane Center (NHC) upgraded investigation area 93L to named storm Julia.
This was a huge surprise for many other meteorologists as well and likely even caught the NHC off guard: Just nine hours earlier they had only given the system 40% chance (image below) and 12 hours prior only a 20% chance of development over the next 48 hours. In fact, the NHC didn’t even classify the system as a depression – the system went straight to a named storm. So clearly, the system developed rapidly by feeding off the very warm waters off the Florida coast.


A look at yesterday 2 pm EDT NHC 5 Day probability of tropical cyclone formation. At 11 PM EDT they upgraded the storm to Tropical Storm Julia

The other surprising fact is that Julia was overland most of yesterday, and it’s really rare for a storm to be named overland. In fact, The Weather Channel’s Michael Lowry reported that only 2% of all tropical cyclones in the Atlantic have formed over land. But according to Philip Klotzbach at Colorado State University, none of the 2% actually formed over Florida, and Julia will go into the record books as being the first named storm to form over Florida and not make landfall.

The other interesting fact is that the NHC barely acknowledged the overland tropical system that will likely have an economic impact above $10 Billons in Louisiana. So the NHC seems to be making up for this mistake by forecasting that Julia will likely also have large flooding impact across the Southeast U.S. and it should have a name like the Louisiana system should have had a name.  It’s possible, but I have been clear that the NHC plays name games with systems, and the storm name (or lack thereof) is less important than the storm impact.

TS Julia will remain overland, quickly weaken today to a Tropical Depression, and park itself over Southern Georgia where it will cause flooding rain (which is likely to be the main insurance impact).


Tropical Storm Julia Rainfall Forecast showing 2 – 8″ of rain over the next 72 hours over the southeast coast of the U.S.

Tropical Depression 12 just formed near Cape Verde and will struggle to move generally west over the next several days. At this time, is not a threat to the insurance industry. Named storm Karl should be expected later today.

Peak Season

September 10 marked the statistical peak of the Atlantic hurricane season. Based on data gathered since 1851, it’s more likely for a named storm to be active on this date than on any other date in the entire season — from June 1 to November 30. However, this year brought no named storm on September 10. This absence has only occurred in 12 of the past 50 years.
Although Julia’s progression highlights issues with the inconsistency of naming named storm, this year’s count is above normal so far this year. The average date for 11th Atlantic named storm is Nov. 23 and Karl is expected to be named later today. In terms of Accumulated Cyclone Energy (ACE), the basin as a whole is 75% below normal with Hurricane Gaston generating more than 59% of the total ACE this season.


As I predicted at the start of the season, storms have struggled to develop in the Main Development Region (MDR) of in the Atlantic Ocean and have developed closer to the U.S. This is due to the large amount of dry dusty air in the atmosphere in this area of the Atlantic basin. This should result in storm having a better chance to form closer to the U.S.

For the Remainder of the Season

The insurance industry should expect more of the same. With warm water, less shear and dry air near the U.S. coastline, conditions are ripe for storm development. The ECMWF ensemble % chance of tropical cyclone development guidance might be the best way to sum up the current and future activity of tropical cyclone activity over the Atlantic Basin over the next two weeks.  As overall I expect less activity over the basin next week as an large scale area of sinking air moves over much of the basin next week.  As of right now besides Julia I don’t expect any U.S. insurance industry concerns over the next two weeks.


BMS Tropical Update 9/3/2016 9 AM CDT

Hermine is about ready to write chapter four.  Chapter 1 – Unwillingness to develop across Atlantic.  Chapter 2 – Tropical depression in Gulf.  Chapter 3 – Southeastern landfall impacts ending the 10 year Florida hurricane drought.    Now chapter 4 is starting, which should be Northeast impacts.   Like many storms of the past, as storms exit back over the warm waters of the Gulf Stream and the frictional effects of land lessen, storms can easily intensify and over the next 24 hours this is what is expected with Hermine.

Gif Created on Make A GifHowever, it should be noted that this next chapter will not be similar to Hurricane Sandy.   I have seen a few reports that Hermine will be the next Superstorm Sandy, AKA Superstorm Hermine.   This is just a function of the 24/7 weather information era, social media hypecasters, and click bait that is all to common.   Each storm is different and it is easy to lock onto analog storms. I am guilty of doing that often.

However, Hermine is not Sandy, where are many differences between the two storms:

The setup is obviously different .  Sandy came up from the Bahamas and Hermine from the Gulf of Mexico so two totally different directions.

Sandy was a 940 mb low pressure system moving towards the New Jersey coastline with tropical storm force winds 1000 miles across and over 90 mph along the New Jersey coastline.   Hermine will have a low pressure center around 990 mb which is much higher and the tropical storm force winds will only extend out, less than 350 miles according to the latest National Hurricane center forecast.  However, both will likely be hurricanes off the New Jersey shore, but again this depends on how textbook the National Hurricane center is with the classification.


Sandy 850 mb winds and mean sea level pressure on the Left.  Hermine 850 mb winds and mean sea level pressure on right.

Sandy’s wave heights were historic at 30ft+   Hermine’s waves are only expected to be 20ft with maybe a few reports of 30ft.


Sandy Wave Height Left and Hermine Wave Height Right.


What will make Hermine impactful is this looks like this will be a long duration event. This means waves and wind will batter the northeast coastline for days, not hours like Sandy did.   There is still some track uncertainty and clearly the closer Hermine tracks to the coastline the worse the winds will be.  One can expect, given the long duration of strong winds, minor structural damage could occur.

Currently the Verisk Climate wind model which can be viewed in BMS iVision suggest these tropical storm force winds > 39 mph will not be impacting the New Jersey coastline, but this could change with the next few model runs.


This will also create coastal flooding problems with some area seeing close to record flooding which will be similar to Sandy along parts of the New Jersey coastline.

Instead of posting various flood forecast along the shore please go to the following site for the latest surge and flood information as these forecasts will change daily. 

At this time I don’t think the new National Hurricane Center storm surge inundation maps are capturing the full impact of the coastal flooding. 

BMS Tropical Update 9/2/2016 12 PM CDT

Hermine made landfall near St. Marks, Florida, around 1:30 am EDT with winds of 80 mph, making it a strong category 1 hurricane at landfall. As predicted, flooding rains, storm surge and tree fall have been the biggest insured impacts and overall should result in a minimal loss for the insurance industry. The storm has now weakened to a tropical storm near Savannah, Georgia. However, as mentioned in previous posts, Hermine will continue to track overland for the next 24 hours and exit the U.S. coastline near the outer banks of North Carolina. Unfortunately however, as we have seen over the last 16 days, the overall energy of this system is persistent. It now appears that Hermine won’t go away any time soon. After Hermine exits the East Coast, it will become a “post tropical” storm. This means that the storm will actually grow in size, and given that the water is as warm as it can possibly get off the East Coast of the U.S., it will continue to fuel Hermine’s circulation.

Below is a look at the warm sea surface temperatures off the East Coast.


Rule of thumb: 26C can maintain a tropical system. 28C can easily intensify it.

After Hermine moves off the East Coast, it will likely merge with a large-scale mid-latitude trough which will slow Hermine’s overall movement. Therefore, all but a few of the forecast models suggest that Hermine will stall over a 3-to-4-day period.


ECMWF ensembles: Most members “Stall” Hermine, some members hook inland, others out to sea. Still some uncertainty watch closely.


Where Hermine takes turn to North and stalls will be an important factor for Mid-Atlantic impacts. The farther east, the better


This is bad new for the barrier islands and beach communities along the Mid Atlantic. Historically high amounts beach erosion will occur with a very constant wind direction for several days. Keep in mind that this constant flow of water will continue to push water into the back bays, and this water will have no outlet. This will result in major coastal flooding, and perhaps even record flooding, along the New Jersey coastline.  The latest extra-tropical storm surge map forecast can be be found here:


Major to record flooding forecast Sunday night for many stations along NJ coastline. Record at Cape May is 9.0 feet from January Nor’easter. These forecasts will change several times a day and will depend on the track of Hermine.


The winds over this 3-to-4-day period will be very similar to a strong nor’easter, and regardless of how the system is classified and where it might wobbles off the East Coast, tropical storm force winds could blow in many areas of the coastline. There is even a chance that Hermine could regain hurricane status. I have already made my point this week that the NHC seems to be treating the hurricane classification as a classroom lecture. Right now, the storm’s classification is far less important than its ultimate impacts.

There are very few storms of this size that have stalled off the East Coast. One of those storms was the Ash Wednesday Storm (1962) and Hurricane Esther (1961), both of which produced significant insured impacts along the East Coast.



Hurricane Esther was the first large tropical cyclone to be discovered by satellite imagery.

Great video talking about the storm of 1962 and the lessons that have been learned and why one might not see the same type of damage today.

BMS Tropical Update 9/1/2016 12 PM CDT

Historically, Labor Day weekend is no stranger to hurricane impacts to the U.S. Coastline, and this year is no exception. After all, the peak of the season is just ten days away. With winds of 65 mph, Tropical Storm Hermine is less than 10 mph from being classified as a hurricane. And located 170 miles southwest of Apalachicola, Florida and 220 miles west southwest of Tampa, Hermine threatens insured losses. Several models are now coming around to the idea that the long-standing Florida hurricane drought of 3,966 days will soon end. As a reminder, the last Florida landfalling hurricane was Wilma that struck on Oct 24, 2005, near Cape Romano. (You may also recall category 2 Hurricane Arthur, but despite its landfall in 2014, it failed to cause significant insured losses.)

So will Hermine cause large insured losses? Unfortunately, we cannot depend on historical data to help predict since there is little hurricane history in Hermine’s expected path. The three best analog events for the forecasted landfall location are Hurricane Alma (1966), Tropical Storm Allison (1995), and Storm #5 (1941). Storm #5 and Alma were category 2 hurricanes at landfall, so finding a good benchmark historical hurricane to estimated insured loss is difficult in this case, but given these historical events and the hazards outlined below, a multi-million dollar insurance industry loss cannot be ruled out.

The factors that will lead to insured loss at this point will be multifaceted.

Flooding Rains and Storm Surge

Many areas along the Florida Gulf Coast have already seen significant rainfall. Here is what has fallen so far.

Many areas of northern Florida will see between 3” – 12” more of rainfall through Saturday. And although the forecasted area of landfall is mostly made up of large tidal marshlands resulting in a coastline that is not as densely populated, it is very prone to storm surge.

Storm surge could top several feet in some areas, despite the fact that Hermine will be a minimal hurricane at landfall.  In fact, data suggest Hermine has the kenetic energy of a category 1 hurricane already.


Using Verisk Climate forecasted wind swath, BMS clients can now better understand wind impacts to specific risks. This high-resolution model wind field shows hurricane force winds rapidly weaken inland due to frictional effect.


But this does not mean the winds won’t be strong enough knock down some trees, especially given the moist soil conditions in the area. In fact, this section of Florida is not just beach. There are quite a few trees in the north, especially around the Apalachee Bay. When you combine the foliage with the lack of a 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.   One also can’t rule out a tornado or twoSoutheast_biomass



After Florida Landfall
Even though modeling over the last 14 days has not been the best for Hermine, it is starting to come around. Much depends on the track Hermine takes once inland over Florida. If Hermiane tracks back out over the warm waters of the gulf stream, expect Hermine to re-strengthen into a powerful coastal storm. There is some model disagreement about whether Hermine will become a hurricane again, or a post-tropical storm, but regardless, high surf and strong winds will result. Some models even stall Hermine for a few days off the New Jersey coastline near Labor day. The strength really depends upon whether Hermine stays overland along the east coast of the U.S. or just off shore.

Lastly we are still watching Invest 92L  in the Atlantic.  It is fighting dry air and weak so there is no threat at this point in time of development.

Interesting Point
The first Tweet was sent on March 21, 2006, months after Wilma in 2005. Hermine is likely Florida’s first hurricane in the Twitter era.


BMS Tropical Update 8/31/2016 12 PM CDT

Update:  12:55 CDT   has officially been upgraded to Tropical Storm .  Because of Aircraft observation from hurricane hunter.  Not because of satellite, ship, or drone observations. 

Tropical Depression (TD) #9
The insurance industry needs to continue to focus on Tropical Depression (TD) #9 which has been trolling the industry for 14 days. It refuses to take the next step to become named storm “Hermine.” If I had a dollar for every time a model suggested a named storm would develop in the next 12 hours, I would be a wealth meteorologist.

This leads me to the next point: the National Hurricane Center (NHC) classification for storms that approach the U.S. coastline have become increasingly technical in recent years. It is bothersome because it has an impact on the insurance industry. Sandy is a recent example of how technical the NHC storm classification has become. Sandy was downgraded from a hurricane to a post-tropical cyclone less than 100 miles from the New Jersey coastline. With TD #9, countless observations many have suggested that TD #9 should have been a tropical storm. In fact, a ship just recently observed winds of 35 kts.

Even the NOAA Global Hawk Drone aircraft that spent 24 hours observing the storm found tropical storm winds.

This bothers me because back in early 1900’s, storms were classified based on simpler information, such as ship observations. There were no drone aircraft or various other heavily scientific equipped aircraft flying into storms to examine the exact center of circulation. The historical catalogs that are used to create today’s catastrophe models have always used ship reports and flooding rain reports from newspapers to suggest a named storm was likely in the area. This was how storms were classified before all this great technology that allowed the NHC to become so technical. This additional technical information skews modern-day historical catalogs from how it would have otherwise been classified, and it could influence catastrophe models understanding of future named storm risks.

However, storm category is less relevant to the insurance industry at this point in time. The industry needs to focus in on impacts, regardless of what category is ultimately assigned to the system in the Gulf. Which is another lesson learned from Sandy, even a non-hurricane can have hurricane impacts. TD #9 will likely have impacts similar to hurricanes as it tracks northeast over the next several days and makes landfall Thursday night somewhere north of Tampa in the Big Bend region of Florida.



Florida Threats
The main threat at this time is heavy rainfall and flooding. Many parts of Florida will continue to experience heavy rain with a 3” – 13” swath of rain predicted across much of northwestern Florida. Flooding is expected in inland areas and coastal areas as well, as the Big Bend region of the coastline is prone to storm surge. The NHC now issues very detailed storm surge forecasts with every advisory.



Depending on the strength of TD #9 at landfall, winds may gust strongly enough to cause tree damage and power outages. An absence of recent hurricanes made the area ripe for tree falls. Soil moisture is already above normal for the projected landfall area, and even a weak gust of wind can down unhealthy or overgrown trees. A good natural cleaning of foliage can be expected.

Lastly, along with any tropical system there is always a risk of isolated tornadoes. The northern and central parts of Florida and far southern parts of Georgia are at risk as the center of the system moves across Florida later this week.

BMS clients can preview many of these hazards by using iVision to better understand their exposure to the upcoming event.

Post-Landfall Florida
Some models suggest that after the system makes landfall in Florida, it could hang around off the East Coast and maybe even make a second landfall in the Northeast later next week. But before we examine the storm’s next move, we need it to move to the Northeast from its current stationary location.

BMS Tropical Update 8/29/2016 12 PM CDT

The next three weeks are traditionally the peak of the Northern Hemisphere tropical cyclone season. Mother Nature surely knows as there are now eight tropical systems to watch across the Northern Hemisphere:
• Five are being monitored for landfall over the next five days.
• Four threaten the U.S. coastline.
• Two have been classified as Hurricanes Madeline and Lester, and both are in the East Pacific tracking westward towards Hawaii. Madeline will closely approach the Big Island of Hawaii on Wednesday night, and if the track holds, Lester is forecasted to move past the Big Island on Saturday.
Tropical Depression (TD) #8 is located 210 miles east the Outer Banks of North Carolina and will make close approach to Cape Hatteras, all before turning back out to sea tomorrow night. At this time, no insured loss is expected with this system as tropical-storm force winds are expected to remain just offshore.
TD #9 is our old friend Invest 99L that, after much fanfare last week, took 11 days to develop into a tropical depression. This system still needs to be watched closely as it has the highest potential to impact the insurance industry. Although the upper air conditions (Strong Wind Shear) are not ideal for hurricane development, the sea surface temperatures are very warm off the west coast of Florida. TD #9 should be a named storm later today.
As a result of a cold front that will provide cooler weather over much of the East Coast for the long Labor Day weekend, this will also allow the system to turn to the northeast and lead to a track that will cross northern Florida with landfall in the Great Bend region on Thursday. Thereafter, the track calls for the system to accelerate out to sea off the coast of the south-eastern U.S. TD #9 is expected to continue slight strengthening as it curves northeast in the eastern Gulf of Mexico in the next 36-48 hours. It should be noted that this system has a history during which multiple models over-forecasted storm intensification. Now, based on the current intensity ratings issued by many of the forecast models, the NHC seems to have opted for a more conservative forecast. Below are the current NHC’s chances of winds reaching tropical-storm force in the next 5 days, which are 30% or less at individual locations in Florida.



The biggest impacts to the insurance industry would be tropical storm force winds, which could include minor damage and tree fall damage. Rainfall is expected to be 3” – 6” across much of Florida over the next five days so localized flooding is possible.

Lastly invest 92L  is coming off of Africa and has a 40 – 50% chance of development over next 10 days and is expected to track toward the U.S. coastline similar to invest 99L over the last 11 days.  Let’s hope the drama around invest 99L last week does not lead the insurance industry to disregard the next threat as we approach the peak of the season September 10th.


BMS Tropical Update 8/25/2016 12 PM CDT

In the past six days the insurance industry has waited and watched for tropical wave Invest 99L to develop into a named storm. Frankly, it’s getting tiresome.

Six days ago at this time many models predicted Invest 99L would become a full named hurricane.


Above is the 00z run of the GFS model on August 19th valid for this coming Monday, August 29th, which had Invest 99L at a category 5 hurricane as it safely re-curves away from the East Coast.
It is all but certain this scenario will not play out, and once again, it reemphasizes the point that there can be large model errors that exists in hurricane forecasting. In fact, this reminds me of my February presentation at the Reinsurance Association of America Cat Modeling conference on HypOcane. This presentation examined the large forecasting errors associated with Erika and Joaquine in 2015. These errors led to unnecessary hype due to the over-reliance on numerical models. We can’t forget that forecasting tropical systems it not an exact science. The track errors are improving for named storm forecasting, but intensity forecasting still remains a challenge. Invest 99L highlights these challenges as some models suggested six days ago that there would be a tropical system nearing the Bahamas; however, the intensity guidance was all over the place as shown in the scenario above.


Last 9 ECMWF track forecasts for Invest 99L. The two Gulf coast landfalls were 8-day forecasts and were highly uncertain. This option is still on the table.



Last 26 GFS track forecasts for Invest 99L. All but two focused on Florida. The last few model runs of the GFS model have hard time tracking Invest 99L.

NOAA hurricane hunters continue to find a poorly organized tropical wave southeast of the Turks and Caicos Islands. There are times where tropical-storm force winds have been observed, but a lack of a well defined center of circulation with convection continues which is needed for named storm status. This could change at any time.
So for now, it is the same old story: there is a chance of a storm developing, and conditions west of the storm are ripe for development due to very warm sea surface temperatures, less dry air aloft and lower wind shear environment.

What we know today about Invest 99L:
• Models slow the forward speed of 99L late this weekend into early next week. This lessens the chance that the system will move into the western Gulf of Mexico, and increase the chances the system will move into eastern Gulf of Mexico.
• If a named storm develops, Louisiana/Mississippi/Alabama landfall cannot be ruled out, but models suggest Florida is at peak risk.  Time is however running out as the system tracks closer to Florida.
• Most models provided poor intensity guidance. If the system is ultimately named, hurricane development can not be ruled out due to the warm sea surface environment in the forecasted path of the system.

For the latest track and forecast information please visit:

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.

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.



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.


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.

Tropical Trouble In The Long Range Forecast

Tropical Storm Fiona
A few weeks ago I mentioned the approaching peak of the Atlantic hurricane season (September 10). Peak season means that tropical waves will move off the African coast, and attention will focus on the main development region of the Atlantic Ocean. Peak season also means that every tropical wave will need to be watched, and various media may highlight long-range forecasts of major hurricanes tracking toward the U.S. coastline. However, conditions off the African coast are still not ideal for development due to near-normal sea surface temperatures and an abundance of dry dusty air in the upper parts of the atmosphere (known as the Saharan Air Layer or the “SAL”).

This week the sixth named storm (Fiona) of the Atlantic hurricane season formed from a fairly strong African wave. However, as it tracks slowly west, Fiona is fighting high wind shear and the SAL, and as a result, it continues to be a weak tropical storm located about 1,295 miles west of the Cape Verde Islands. Fiona should continue to track to the northwest over the weekend and will likely stall early next week as a weak tropical depression near Bermuda – if it even makes it that far. So at this time, Fiona does not appear to threaten the insurance industry.

Invest 99L
Unlike Fiona, Invest 99L may be the bigger threat to the insurance industry. Invest 99L is an area of disturbed weather currently labeled by the National Hurricane Center (NHC), and to understand Invest 99L, a football analogy may help. Fiona functions as a lead blocker. She sealed off the SAL, allowing Invest 99L to go wide left into more fertile territory later this weekend: as described in my earlier posts, as tropical systems move closer to the U.S., they are likely to develop and strengthen. Likewise, Invest 99L may intensify as it tracks westward to this more fertile territory.

Invest 99 is worth mentioning because the NHC currently indicated a 50% chance that it will develop into named storm Gaston. They project this system will track into the Leeward Islands over the next five days, and as this storm tracks west, it will encounter increasingly warm sea surface temperatures.


Invest 99L is currently favored by models to develop and strengthen in the coming days. However, as stated, this is also the season when the media tend to highlight a single model run as a doom-and-gloom scenario.

Often this far in advance, these forecasts don’t verify, and all forecast scenarios need to be considered at this time. There are a multitude of scenarios still in the playbook for Invest 99L after all it’s not even a named storm yet.
Below is a look at the U.S. Global Forecast Model (GFS) ensemble model output. In total, this is a model run with 21 different forecasts to create an ensemble. The current forecast run demonstrates the uncertainty in the forecast in terms of track.


Below is a summary of various forecast model intensity guidance as Invest 99L tracks westward over the next five days.


In summary, Invest 99L has a high chance of developing into tropical storm Gaston over the weekend. There is some uncertainty in its long-range forecast track, but we know with high confidence that the system is expected to track toward the western Caribbean where the water is warm enough to support healthy hurricane development. If atmospheric conditions are ideal next week, a potential hurricane could approach insurable risk in the Caribbean and U.S. If these conditions late next week are not ideal, the current tropical wave could be just that – a tropical wave.

Peak of 2016 Atlantic Hurricane Season Is Approaching

It’s hard to believe, but the Atlantic hurricane season began 189 days ago when Hurricane Alex formed on January 13 and went on to become the strongest hurricane ever to form in the month of January in Atlantic Basin. The early season continued with three landfalling named storms that formed this June, making it easy to assume that an early season means an active season. But an early start to the season does not necessarily mean that the heart of the hurricane season will be active. A current lull in the basin since June 21 and long-range forecasts suggest there is limited opportunity for development for the reminder of July. However, climatology suggests we are not out of the woods yet. Instead, we are only just approaching September 10: the peak of the season when storm formation becomes much more frequent.

This is the time of year when eyes are trained on the massive cloud clusters that move off the West African coastline. These clusters have been limited so far this season. The only movement off this region is massive plumes of Saharan dust.


Current CIMSS Tropical Cyclone Team imagery that is useful for monitoring the position and movement of dry air masses such as the Saharan Air Layer (SAL) and mid-latitude dry air intrusions. Animations of the imagery are useful for tracking these features and can also help identify the source of the dry and/or dusty air that is indicated in the imagery.

In some cases, these dust plumes have traveled all the way to the Texas Gulf Coast. Known as the Saharan Air Layer (SAL), this dry, dusty air has about half the moisture of the typical tropical atmosphere and can discourage the clouds and tropical convection needed for named storm development. Although we still lack a full understanding of how the SAL affects tropical systems, there are likely several reasons why it limits cloud and tropical convection development, and thereby limits the likelihood of named storm development.

  • Dry air can enhance downdrafts (sinking air), suppressing convection around the system.
    As tropical waves move off Africa, any resulting convection quickly reaches the bottom of the SAL (typically at altitudes between 5,000 and 15,000 feet); then entrains dry air which limits further convection.

Here is the current 850 mb temperature normalized anomalies which shows that areas of heavy dust have warmed the atmosphere at this level 3 – 5 degrees Fahrenheit.

  • Typically atmosphere cools with height, but the SAL absorbs sunlight, which retains warmth and creates an inversion for thousands of miles across the Atlantic basin. This essentially caps the development of the showers and thunderstorms that are needed in tropical cyclone development.
  • Dusty conditions can be enhanced by stronger easterly winds that increase wind shear and tilt or outright displace the convection aloft from low-level circulation, thus limiting convection and tropical cyclone development.
  • The SAL shields sea surfaces from the sun and can keep the sea surface temperatures cooler than normal across the main development region.

Data suggests decadal variability in the SALs that may impact tropical activity (unfortunately, since the insurance industry doesn’t need another multi-year decadal pattern that could influence tropical cyclone development). Records going back to the 1960s and 1970s that were collected by satellites and island stations (using dust as a tracer) show that SAL activity have ebbed and flowed over the years. In the 1980s, some studies point to quiet periods that coincided with a stretch of increased dust outbreaks. In the 1990’s, dust activity decreased and tropical cyclone activity began ramping up.
At this time it is difficult to say if the dry, dusty air will continue into the heart of the Atlantic Hurricane season which effectively peaks around September 10th. We are only one-third of our way through hurricane season, and June and July are not usually good indicators of what is to come: on average, those months account for only 4% of Atlantic major hurricane activity.


— Philip Klotzbach (@philklotzbach) July 20, 2016

And just as a reminder, the 2004 named storm season didn’t have its first named storm form until August 1, but 2004 ultimately became one of the most active seasons on record for U.S. Florida landfalls.

The insurance industry shouldn’t let its guard down. If the dust persists and Cape Verde storms are hampered by the SAL, storms may instead develop in the western Atlantic which provides a higher likelihood of making U.S. landfall. And given the Western Caribbean and Gulf of Mexico is experiencing record warm surface temperatures and heat content, there is plenty of energy for these storms to become powerful hurricanes should they track over such warm waters.


Total oceanic heat content (called the Tropical Cyclone Heat Potential, or TCHP) in kilojoules per square centimeter (kJ/cm^2), for July 15 for the years 2005 – 2016. TCHP was at near-record or record values over much of the Caribbean, Gulf of Mexico, and waters surrounding the Bahamas in July 2016. TCHP in excess of 90 kJ/cm^2 (orange colors) is commonly associated with rapid intensification of hurricanes. Image credit: NOAA/AOML.

In summary, El Niño is gone and La Niña conditions are slowly building in the Central Pacific, and the SAL is currently hampering development in the main development region of the Atlantic. Long range forecast models remain quiet with little development chances. However, the warm ocean heat content and sea surface temperatures near the U.S. coastline would provide plenty of fuel for a strong hurricane if one were to track over these waters.