July 31st, 2020 Analytics, Atlantic Hurricane Season, Insights

BMS Tropical Update 07/31/2020

By Andrew Siffert – Vice President / Senior Meteorologist

Despite all the negative impacts discussed in the last tropical update, Isaias developed into a hurricane off the Hispaniola northern coastline last night. This morning Isaias is not a perfect example of a category 1 hurricane, as the stronger wind shear that was discussed in the last update continues to limit its overall strengthening. With that said, Isaias is fighting back with deep convection as strong winds and heavy squalls lash the Southeastern Bahamas and the Turks and Caicos islands. The center of the storm is located 245 miles Southeast of Nassau, Bahamas with maximum sustained winds of 75 mph.

The insurance industry is no stranger to the current track, forecasted by the National Hurricane Center (NHC). It shows Isaias tracking up the East Coast of Florida and possibly turning toward and impacting the Carolinas.


Based on this forecast, there are plenty of reports showing recent analog impacts for the insurance industry to use in understanding them. In 2016 Hurricane Matthew tracked dangerously close to the Florida coastline as a category 4 and 3 hurricane causing about $1 billion to the insurance industry without making landfall. Just last year, Dorian, a powerful category 5 spun for days over the Bahamas before weakening to a category 2 hurricane and tracking along the Florida east coastline causing $127M in insurance loss without making landfall. However, we also know that some tropical storms, like Julia in 2016, track right along the Florida coastline without causing enough insurance industry loss for a PCS CAT designation. In all these cases the critical factors are the distance the storm is tracked from the Florida coastline and the size and strength of the system. Knowing what we know, what should the industry expect with Isaias?

The forecast for Isaias Florida Impacts

The overall high wind shear environment impacting Isaias will last another 24 hours so there is still a bit of uncertainty with how the forecast will play out. The newest run of the world-leading ECMWF model shows Isaias as a weaker category 1 hurricane or strong tropical storm into South Florida. This would likely have limited impacts on the insurance industry given the recent storms to impact the area that have been stronger, such as Irma in 2017. However, any storm into South Florida will likely compound other issues the state has been dealing with for years now around Assignment Of Benefits (AOB).

The latest couple runs of the ECMWF ensemble, representing 51 different forecast perturbations, suggests forecasts of either tropical storm or major hurricane tracking along the East Coast of Florida over the next 72 hours. If Isaias continues to maintain its overall environment, fight off wind shear and dry air on Saturday, the overall environment will be much more conducive for a stronger hurricane formation as there is plenty of warm water temperatures from the Gulf Stream between Florida and the Bahamas. As mentioned in this scenario the track and size of the storm are critical to the insurance loss impacts. Matthew in 2016 is likely a good analog of what to expect if a stronger storm tracks along the coastline, we can also look to Dorian, in 2019, in terms of what to expect if a stronger storm is closer to the Bahamas. The NHC official seems to favor a track between Dorian and Matthew as a modest category 1 hurricane. If this is the case, a tropical storm condition could be experienced between Stuart to Smyrna Beach, FL. In summary, the insurance industry loss for Florida depends on the overall track which still has some uncertainty, but Matthew and Dorian provide a good idea of potential bypassing hurricane impacts.

Above is a view of this mornings ECMWF ensemble which called the spaghettios plot showing the low-pressure center of each of the storms forecasted by the ensemble over then next 144 hours, which again favors a track closer to Florida. Clearly there is a range of possible outcomes regarding the exact track and intensity which would mean a coastal location could experience 30 mph winds vs 60 mph winds in Florida and places in the Outer Banks could experience 60 mph winds vs 100 mph winds. Storm surge would follow along similar lines (1-3 ft versus 3-5+ft).

Above is the BMS iVision Verisk Respond Hurricane 3 sec wind gust layer showing the strongest winds will be well off the Florida coastline as the storm tracks along the coastline. It also shows how the strongest winds of a hurricane are on the right side of the center which would be even further away from the coastline.

Mid-Atlantic and Northeast Isaias impacts

Above we paint the picture for what to expect over the next 48 hours. With the different forecast scenarios and the potential impact on Florida on the table what happens after Sunday will depend on the interaction with the Florida coastline. Regardless on Sunday, the upper-level environment over eastern North America will undergo some fairly dramatic changes as a trough digs into the Central U.S. ahead of that trough, upper-level winds West of Isaias will become more southerly. This will result in shear over the storm lessening and perhaps some beginning intensification. This upper-level trough will also leave Isaias with no choice but to turn north-northeast and accelerate. There are still small-scale track uncertainties to iron out that will be consequences for the insurance industry. A track that wobbles farther west would bring wind damage and heavy rain to a wider swath of the East Coast, but given the track and forward speed of the Isaias storm surge, damage would not be quite as intense. A track farther east away from the coastline would lower the risk of impacts to the Southeast coastline but could make for a much stronger storm in New England as it feeds off the warm Gulf Stream waters which are some of the warmest in the Atlantic Basin. There is a chance the storm could miss the East Coast altogether, sliding just far enough offshore to spare the worst impacts.

With continued uncertainty after 48 hours in the track and growing intensity of Isaias, we could possibly see dramatically different impacts. This will be addressed in the next tropical update, as we learn more over the next 24 hours about what will happen to Isaias. In the meantime, the insurance industry should keep an eye on the latest NHC Offical cone of uncertainty and remember to not focus on the exact track. We also need to keep in mind intensity forecasts for named storms so far in 2020 have been a dumpster fire showing very poor skill so expect more surprises as the 2020 Atlantic hurricane season continues to unfold.