A area of disturbed weather over the warm waters of the Gulf Stream current off the Southeast U.S. coast has been designated Invest 91L
by NHC. Satellite loops
on Saturday morning showed 91L with only a small amount of heavy thunderstorm activity that was poorly organized. There was no hint of a surface circulation trying to form. Long-range radar
out of Melbourne, Florida showed a few modest areas of rainfall over the ocean about 50 - 150 miles east of the Central Florida coast. Sea surface temperatures in this region were about 1°C above average, 27 - 28°C--plenty of heat energy for a developing tropical cyclone. Wind shear
was moderate, 10 - 15 knots. The shear was due to strong upper-level winds out of the north, which were keeping any heavy thunderstorms from developing on the north side of 91L. Water vapor satellite loops
showed that the atmosphere was moderately moist off the Southeast U.S. coast, and dry air should not be a significant impediment to development. The Hurricane Hunters are on call to investigate 91L on Sunday afternoon.Figure 1.
Latest satellite image of 91L.Forecast for 91L
The 12Z Saturday run of the SHIPS model
showed light to moderate shear, 5 - 15 knots, over 91L for the next five days. With the disturbance parked over the warm waters of the Gulf Stream, organization into a tropical depression is a good possibility. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave 91L 2-day and 5-day development odds of 30% and 50%, respectively. As of noon EDT, I'd put these odds higher, at 40% and 60%, respectively. Steering currents are weak off of the Southeast U.S. coast, and the uncertainty in the track of 91L is higher than usual. The 00Z Saturday run of the UKMET and European models
predicted a slow motion to the northeast, with the European model showing a potential threat to the North Carolina coast by Thursday. The 00Z and 06Z Saturday runs of the GFS model
predict the opposite motion, a slow track southwestwards with a landfall in Florida on Tuesday. None of these models showed 91L reaching tropical storm strength. The UKMET and European model have been pretty consistent with their recent runs, so I favor their solution of a more northeasterly motion for 91L over the next five days.
I'll have an update on Sunday.