Tropical Depression Seven Forms, Impacts to Eastern Caribbean Possible This Weekend

Lead Forecaster Daniel Crawley

Good Wednesday evening to everyone. Not much going on in the weather department locally, so lets talk tropics…

Tropical Depression Seven formed late this morning several hundred miles east of the Lesser Antilles. As of 7 pm Wednesday water vapor imagery shows a good bit of convection blossoming along and east of the low pressure associated with TD-7. This is the only feature going on in the Atlantic Basin as things remain quiet compared to the climatological norm.

The latest National Hurricane Center Forecast has TD-7 moving gradually west toward the Lesser Antilles by this weekend as a tropical storm.

National Hurricane Center Forecast (Wed 5 pm)

Synoptic Discussion…

A broad 500mb ridge is located in the Central Atlantic Ocean with a developing 500mb ridge across the Central and Southeast US. There is a weakness in-between those two ridges centered near the Bahamas. This general setup is expected to continue through the upcoming weekend, so the first 3-4 days of the forecast is straight forward. Differences arise later in the forecast cycle.

From an atmospheric setup, TD-7 will have to battle some dry air, shear and ultimately landmasses such as Puerto Rico and Hispanola by Day 4-5. So the expectation is slow intensification will occur through Saturday and then a slight weakening as landmass interaction could occur.

The ultimate track of this storm long term has a ton of question marks. Intensity could impact the short term motion of the storm and that could then ripple to changes in the track past Day 5.

Global model ensembles has a fairly wide range of low positions ranging from near Jamaica to the Southeast Bahamas by early next Tuesday…generally a slow intensification of TD-7 leads to the further southwest positions where a quick ramp up could tug the feature north following that weakness at 500mb.

12z Euro ENS Low Positions (Tues Sept 20, 8 am)

Hurricane guidance is a bit more clustered and seems to be the origin of the current NHC forecast for TD-7…it shows a lot more interaction with Puerto Rico and Hispaniola by late Sunday and Monday. There are members in the tropical guidance suite that also shows the tug northward as well acknowledging the 500mb height pattern. These individual members that curve likely indicate a stronger system as well.

If you have vacation plans or general interest in the Eastern Caribbean for this weekend and early next week, pay attention to future forecast updates on the intensity and track of TD-7.

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