Tropical Disturbance May Develop off Southeast U.S. Coast by Monday

A blow-up of thunderstorms over Texas and Louisiana on Wednesday created an area of low pressure that tracked east-northeast over the Southeast U.S., and was over Georgia and South Carolina on Friday. This low will emerge over the coastal South Carolina waters on Saturday, and move over the warm waters of the Gulf Stream current by Sunday. Sea surface temperature in this region are about 1°C above average, 27 - 28°C, which is plenty of heat energy for a developing tropical cyclone. Wind shear is moderate, 10 - 20 knots, and is forecast to remain moderate through Monday. These conditions favor development, though the 00Z Friday runs of our reliable tropical cyclone genesis models--the GFS, European, and UKMET--did not show development into a tropical depression. The disturbance will be in an area of weak steering currents, and the predominant track favored by the models is a slow south and then southwest movement towards Florida. The latest thinking from NOAA's Weather Prediction Center (Figure 1) is that the disturbance will bring a swath of 2 - 4" of rain from North Carolina to Florida during the coming week. These rainfall totals will be higher if the disturbance develops into a tropical depression. However, the system may not have much time over water before moving ashore over Florida on Monday, if the 00Z and 06Z Friday runs of the GFS model are correct. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odds of development of 0% and 20%, respectively.


Figure 1. Predicted precipitation for the 7-day period ending on Friday, July 4, 2014. A tropical disturbance off the Southeast U.S. coast is predicted to create a swath of 2 - 4 inches of rain from North Carolina to Florida. Image credit: NOAA's Weather Prediction Center.


Figure 2. There's nothing cooking off the coast of Africa: the tropical Atlantic was dominated by stable stratocumulus clouds and was free of heavy thunderstorm activity in this MODIS image taken on Friday morning, June 27, 2014. The murky appearance of this image is due to Saharan dust sweeping westwards off the coast of Africa. In the lee of the Cape Verde Islands, we can see beautiful Kármán vortex street clouds--a repeating pattern of swirling vortices caused by the unsteady separation of flow of air around the islands. The phenomenon is named after the engineer and fluid dynamicist Theodore von Kármán. Image credit: NASA.

Have a great weekend, everyone, and I'll have at least one update over the weekend.

Jeff Masters