Tropical Depression One Forms off the Coast of East Florida

The Atlantic's first tropical depression of 2014 is here, as Tropical Depression One finally formed at 11 pm EDT Monday evening from disturbance 91L. TD 1 was drifting southwest at 2 mph towards the east coast of Central Florida early Tuesday morning. Long-range radar out of Melbourne, Florida on Tuesday morning showed that bands of heavy rain from TD 1 were affecting the Northwest Bahamas, and sustained winds of 33 mph gusting to 36 mph were observed at Settlement Point in the Northwest Bahama Islands at 2 am EDT. Satellite loops showed heavy thunderstorms were limited to the south side of TD 1's center of circulation, and were slowly increasing in intensity and areal coverage. The counter-clockwise circulation of an upper level high pressure over Florida was bringing northerly winds over TD 1 at high altitude, and these winds were creating moderate wind shear of 10 - 15 knots. Water vapor satellite loops showed very dry air to the north of TD 1, and the northerly winds were driving this dry air in the heart of the storm, interfering with development, and keeping any heavy thunderstorms from developing on the north side of the circulation. The Air Force Hurricane Hunters will investigate TD 1 on Tuesday morning, and the NOAA jet is scheduled to fly Tuesday afternoon.


Figure 1. MODIS satellite image of 91L, taken at approximately 16:30 UTC (12:30 pm EDT) on Monday, June 30, 2014. Image credit: NASA.

Forecast for TD 1
Steering currents are weak off of the Southeast U.S. coast, but the models are in good agreement on the track. The disturbance should continue a slow southwesterly motion through Tuesday morning, then turn northwards or north-northwestwards on Tuesday afternoon, and move parallel to the Florida coast without making landfall in Florida, as the storm responds to a trough of low pressure passing to the north. Heavy rains of 2 - 4" will likely affect the Northwest Bahamas and eastern coast of Florida Tuesday through Wednesday. By Wednesday, the models are in agreement that TD 1 will turn northeast without hitting the coast of South Carolina, but potentially pass very near the Outer Banks of North Carolina on Friday morning. The 6Z Tuesday run of the SHIPS model showed the atmosphere surrounding TD 1 will stay dry this week, with the wind shear staying light to moderate, near 10 knots. This dry air, in combination with potentially moderate wind shear, should keep development slow. The storm will be over the warm waters of the Gulf Stream, so the extra heat energy available to the storm will help counteract to dry air and wind shear, though. The official NHC forecast of a high-end 70 mph Tropical Storm Arthur on Friday, as the storm makes its closest approach to North Carolina, is a reasonable one. A much weaker storm is also possible, if dry air and wind shear continue to interfere with development this week.

I'll have a new post by Tuesday afternoon.

Jeff Masters