A well-organized tropical wave rolling through the northeast Caribbean, Potential Tropical Cyclone 6, was on track to bring heavy rains and gusty winds to the Greater Antilles into Wednesday, and it may affect parts of Florida and the eastern Gulf of Mexico toward the weekend and early next week.
As of 8 p.m. EDT Tuesday, the ill-defined center of PTC 6 was located about 30 miles south of the southern coast of Puerto Rico, with top sustained winds of 40 mph. The system was moving west at around 17 mph. Based on the assumption that PTC 6 will become Tropical Storm Fred on Tuesday night, a tropical storm warning was in effect for Puerto Rico, the U.S. Virgin Islands, and the eastern coastline (north and south) of the Dominican Republic. Tropical storm watches extended to other parts of the Dominican Republic and Haiti, and also to the Turks and Caicos Islands and the Southeast Bahamas.
Although it was plowing into a large field of relatively dry air, PTC 6 managed to retain a fairly moist core. On Tuesday, ample showers and thunderstorms (convection) had begun to wrap from PTC 6’s north side toward its southern half. Spin was clearly evident on satellite imagery, and on radar displays from Puerto Rico. PTC 6’s broad circulation extended to well east of the Leeward and Windward Islands. Despite the impressive larger-scale structure, PTC 6 lacked a single closed low-level center of circulation, so it could not be yet classified as a tropical storm even though its peak winds of 40 mph were strong enough to qualify.
Forecast for PTC 6
PTC 6 will likely become no more than a low-end tropical storm through at least Thursday, and it could easily cross from tropical storm to tropical depression status or back. The main threat to Puerto Rico and Hispaniola will be heavy rain and the potential for flash flooding and mudslides. Rains of 2-4” will be widespread, with localized amounts up to 6”.
PTC 6 will be crossing Hispaniola on Thursday and then moving west-northwest roughly parallel to the north coast of Cuba by Friday, so the circulation will be significantly disrupted by land for some time. Often when such systems cross Hispaniola, a center will form (or reform) just north of the island. PTC 6 will have a better chance of restrengthening if the eventual center tracks at least 50 or 100 miles north of Cuba rather than near or atop it.
By Friday, the center of PTC 6 is projected to be angling away from Cuba toward the Florida Straits. The official NHC forecast as of 5 p.m. Tuesday brings PTC 6 near the Florida Keys as a tropical storm on Saturday.
PTC 6 is being steered by a broad ridge of high pressure extending from the western Atlantic into the eastern United States. As PTC 6 rounds the southwest end of this ridge, it is expected to take on a more northwest or north-northwest track by this weekend, which will most likely bring it into the eastern Gulf of Mexico, as depicted by the 12Z Tuesday runs of the European and UKMET models. The 12Z Tuesday GFS track is the easternmost of our three top track models, bringing PTC 6 across southernmost and southwest Florida over the weekend. Such a path is within the NHC’s cone of uncertainty.
If PTC 6 takes the most easterly plausible track late this week – staying well north of Cuba and approaching the southeast coast of Florida, along the east side of the official NHC cone – it will need to be watched especially closely. Both of our top regional intensity models, the HWRF and HMON, depicted such a track in their 12Z Tuesday runs, showing PTC 6 possibly reaching the southeast Florida coast as a tropical storm or hurricane late Friday or Saturday. However, these intensity forecasts are highly contingent on such a track, and the HWRF and HMON are not among the top track models, so it is much too soon to trust such a possibility – especially since it is at odds with the current NHC forecast.
Should PTC 6 end up tracking well offshore across the eastern Gulf, it will have a fair shot at attaining at least minimal hurricane status. SSTs are quite warm, and wind shear will be decreasing along PTC 6’s path by the weekend. The official NHC forecast brings PTC 6 to top winds of 70 mph (just below hurricane force) by Sunday, when the system is predicted to be approaching the Florida Panhandle.
Another system that bears watching in the eastern Atlantic
A compact disturbance in the eastern tropical Atlantic between longitudes 25°W and 30°W has been named 95L, and it may slowly organize as it moves westward at 15-20 mph. We are now entering prime Cape Verde season, the time of year when tropical waves moving west off the African coast have the best chance of developing long before they reach the Caribbean or the U.S. East Coast.
95L was undergoing moderate to strong wind shear (15-25 knots) on Tuesday. This shear should relax to 10-15 knots by later in the week, and the disturbance will be passing over increasingly warm waters (around 28°C or 82°F). The mid-level relative humidity along 95L’s track will be around 60%, which is also favorable for development.
In its 2 p.m. Tuesday tropical weather discussion, NHC gave 95L a 10% chance of developing into at least a tropical depression by Friday and a 20% chance by Sunday. It’s too soon to know whether 95L will affect North America or the Caribbean. However, long-range models suggest that the hefty ridge over the western Atlantic may hold firm through next week and help keep systems in the tropical Atlantic from recurving safely out to sea.
“The overall environment for this particular wave looks rather favorable, particularly on the European ensemble, with very little dry air or TUTTs around and a strong, upper-level anticyclone directly overhead,” tweeted meteorologist Eric Webb (@webberweather) on Tuesday morning.
Jeff Masters contributed to this post.
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