Morning GOES visible satellite image look at tropical system "99L"; courtesy Penn State eWall, NOAA
Amazingly, the state of Florida has not had a hurricane of any intensity since Wilma came ashore in southwestern Florida during late October of 2005. Hurricane Wilma was also the last major hurricane (i.e., category 3, 4 or 5) to strike US soil in what has turned out to be another amazing streak. Both of these streaks are unprecedented in the record-keeping era and both may come to an end by this time next week.
Current steering winds in the lower and middle parts of the atmosphere which favor a movement towards Florida and the Gulf of Mexico; map courtesy University of Wisconsin/CIMSS
As the climatological peak of the Atlantic Basin hurricane season approaches (i.e., mid-September), we have an active scene with two different tropical systems. In the eastern Atlantic Ocean, Tropical Storm Gaston has maximum sustained winds of 70 mph and could reach hurricane status later today. It is moving west-northwest at 17 mph towards the open Atlantic and should stay out-to-sea and not impact the US. Meanwhile, the real area of concern is a broad area of low pressure at the northeastern corner of the Caribbean Sea still officially known as 99L (it’ll become “Hermine” when it reaches tropical storm status). This tropical system is now over the northern Leeward Islands and it is showing more organization today as it churns west-northwest around 15 mph towards Puerto Rico, Hispaniola and the Bahamas. There is growing potential that this tropical system will have an important impact on Florida and the entire Gulf of Mexico region this weekend and into next week.
Predicted storm tracks from multiple numerical models; courtesy NOAA, NCAR
Current steering winds in the atmosphere suggest this tropical wave will continue on a west-to-northwest track over the next few days and computer forecast models tend to agree. This type of wind flow over the next few days will likely steer this storm at or just to the north of Puerto Rico, Hispaniola, and then into the Bahama Island chain. This tropical system is also likely to intensify as it heads over the warmer-than-normal waters in the northern Caribbean Sea and the western Atlantic Ocean. While odds favor a move just to the north of Hispaniola (Haiti/Dominican Republic), a slight shift in that thinking to the south would be important as the mountainous terrain on that island could weaken the tropical system or - at a minimum - slow down its intensification. However, once passed that potential obstacle, the tropical system will likely intensify as it approaches the Bahamas and ultimately, the southern part of Florida. If so, it is possible that the first hurricane since Wilma (October 2005) makes landfall somewhere in southern Florida by the latter part of the weekend - and this would end the state’s unprecedented hurricane drought.
Sea surface temperatures in the western Atlantic Ocean, Gulf of Mexico, and Caribbean Sea (brown areas are greater than 86°F); map courtesy Weather Bell Analytics
After potential landfall in southern Florida by the latter part of the weekend, there are reasons to believe that steering winds will continue to favor a move across the state and into the Gulf of Mexico and some computer models agree with this scenario (e.g., Euro). Strong high pressure will be situated over the Northeast US by the latter part of the weekend and this position favors movement of any tropical system into the Gulf of Mexico - and not a turn up the eastern seaboard. This type of pattern is especially worrisome since this would contribute to low-level convergence over the Gulf of Mexico and combine that with the very warm waters and the result could very well be explosive development. In a large part of the Gulf of Mexico sea surface temperatures are above 86°F and this would be quite favorable for rapid intensification. Ultimately, it is possible that this tropical system could end up slamming into the northern Gulf States – perhaps even as a major hurricane – and the last thing places like Louisiana need is more heavy rain. Beyond that, this tropical system could actually end up producing heavy rainfall in parts of the eastern third of the nation as it ultimately should curve to the northeast.
Meteorologist Paul Dorian