Sally rapidly strengthens into a hurricane as it heads for Gulf Coast landfall

Hurricane Sally has now formed in the Gulf of Mexico and as some forecasts had suggested is now showing the potential for further rapid intensification, with at minimum a Category 1 or 2 hurricane landfall now anticipated on the central Gulf Coast, not far from New Orleans.

This article was last updated at 09:30 BST, Tuesday September 15th: Sally formed at the weekend as a tropical depression, then crossed the Florida keys and southern peninsula and headed into the Gulf of Mexico, becoming the 18th named tropical storm of the season.

Tropical storm Sally has today become the seventh hurricane of the season, as the storm fed off the very warm Gulf sea surface temperatures and is now heading slowly for the Gulf Coast.

So, Sally is set to become the next landfalling hurricane to impact the United States coastline of 2020, a season that has already seen seven tropical storms strike the country and it has the potential to be another storm impact that drives some losses through insurance and into reinsurance markets.

Currently, Sally has maximum sustained winds of 90 mph, with higher gusts and a minimum central pressure of 986 mb that looks set to fall further over the next day.

The NHC said last night that Sally “has rapidly strengthened to a hurricane.” Now the expectation from many forecasters is that Sally reaches at least Category 2 strength, some suggesting it could become a major Cat 3 storm.

Hurricane Sally intensified further to 100 mph winds, but then weakened back to 90 mph as its track jogged around on approach to the coast.

The NHC now says, “Some re-strengthening is forecast early to occur later today, and Sally is expected to be a dangerous hurricane when it moves onshore along the north-central Gulf coast.”

Some forecasts suggest a chance for ongoing intensification, potentially rapid, right up until landfall in the New Orleans region, but also a slow approach with the potential for hurricane Sally to stall over the coast and some concerns building over the potential for prolonged storm surge and significant rains to occur.

Hurricane Sally will pose a major threat to low-lying areas as a result of the slow approach, which forecasters suggest could push a significant storm surge onshore for several hours.

Rainfall levels are also expected to be significant with hurricane Sally and the flood impacts are a concern, while wind impacts are down to just how much the storm can intensify by landfall now.

The NHC forecast now predicts rainfall storm totals of 8 to 16 inches widely and isolated amounts of as much as 24 inches from hurricane Sally, raising similarities to recent years slow moving rain bringing hurricanes such as Harvey or Florence.

With a slow approach expected though and a forecast that suggests intensification right up to landfall, the outlook for hurricane Sally could be particularly dangerous for some areas of the Gulf Coast if the storm reaches significant wind speeds before reaching the shore.

As ever, for the reinsurance and insurance-linked securities (ILS) market, it is wind and surge that drive the largest costs to that end of the market, while rainfall related flooding tends to be largely uninsured, or dealt with by the NFIP.

You can see a modelled intensity forecast for hurricane Sally below (from TropicalTidbits.com):

Reinsurance broker Guy Carpenter explained that Sally will be travelling through an area of the Gulf where, “Both of the best predictors for strengthening are present; namely very warm waters and low wind shear.”

The reinsurance broker also explained that, “Steering currents will gradually slow the system down and bring it onshore along the Central Gulf Coast. The weakening steering currents mean the forward speed of the storm will slow, which is a concern for flooding from both storm surge and rainfall.

“The gradual slowing of the system also increases the uncertainty in the intensity at landfall. The water in the immediate coastal area is very warm; if Sally slows and spends more time over warm water it could allow for additional strengthening.”

Finally, Guy Carpenter said that while official forecasts may point to a Category 1 landfall, “As has been the case all season, the actual intensity and track forecast is still highly uncertain, and interests along the entire Central Gulf Coast, including New Orleans, should be prepared for a hurricane landfall and associated risks.”

Broker BMS Group’s Andrew Siffert explained some of the potential impacts from Sally,”The overall track is very important to the overall insurance industry impacts. As a shift in the current track guidance, east or west could greatly impact the storm surge and wind forecasts for the highly populated New Orleans area as the highest storm surge and wind impacts will be on the northeast side of the track at landfall. Clearly, if Category 1 winds go into the major metro area of New Orleans this will yet again be another billion-dollar loss event for the insurance industry this year.”

Siffert said the bottom line is, “The insurance industry should not take Sally lightly. It is never ideal to have an intensifying named storm approaching the coastline. This intensification will likely occur right up to landfall which puts a bit of a cap on how strong Sally can get; but, as we have seen this year, intensity forecasting has not been great and is a challenge when you have such a wide range of outcomes for the 12-18 hour period right before landfall.

“The angle at which Sally will impact Louisiana and Mississippi will maximize both storm surge and rainfall. Sally is forecasted to be a 90 mph storm. Moving at 5 mph, it will only traverse 150 miles in 48 hrs. New Orleans’ levee systems will be challenged. The angle at which the storm is tracking along the coast and the shallow waters in the area will funnel and raise water levels quickly as Sally ramps up in intensity. Currently, the storm surge is likely to be below 9 feet, but there is a chance that the forecast could change as Sally become better organized and surge values of 10 ft or more are possible.”

In addition, Plenum Investments, the specialist insurance-linked securities (ILS) fund manager, said this morning that based on forecasts of a Cat 1 hurricane Sally landfall it would not expect any exposed catastrophe bonds to be threatened.

Twelve Capital, another specialist manager in the ILS space, also said on hurricane Sally and also Paulette, “While these events are likely to cause dangerous storm surge and potential flooding, they are not forecast to develop into major hurricanes and neither are expected to have any significant impact on the ILS market.”

A peak storm surge forecast map for hurricane Sally from NOAA can also be seen below:

The latest update from NOAA’s National Hurricane Center can be seen below:

Sally is moving slowly toward the west near 3 mph (6 km/h). A slow west-northwestward motion is expected to resume later this morning. A northward turn is expected this afternoon, followed by a slow north-northeastward to northeastward motion tonight and continuing through Wednesday night. On the forecast track, the center of Sally
will move near the coast of southeastern Louisiana later today, and make landfall in the hurricane warning area tonight or Wednesday morning.

Data from the reconnaissance aircraft indicate that maximum sustained winds have decreased to near 90 mph (150 km/h) with higher gusts. However, some re-strengthening is forecast early to occur later today, and Sally is expected to be a dangerous hurricane when it moves onshore along the north-central Gulf coast.

Hurricane-force winds extend outward up to 45 miles (75 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km). A NOAA C-MAN observing station on Dauphin Island, Alabama, recently reported a wind gust of 51 mph (81 km/h), while a buoy just south of Dauphin Island recently reported a wind gust to 59 mph (94 km/h).

The estimated minimum central pressure based on data from the Air Force Hurricane Hunter aircraft is 986 mb (29.12 inches).

At this time storm surges of up to 11 feet are warned for, but that could rise if hurricane Sally manages to intensify significantly on approach to the New Orleans area.

We’ll keep you updated as the situation develops and you can track the tropics over at our dedicated 2020 Atlantic hurricane season page.