Tropical Depression Seven forms
Tropical Depression Seven is here. Looking remarkably like the tropical depression that became Tropical Storm Ernesto on August 1, TD 7 has a limited region of heavy thunderstorms, as seen on satellite loops. A large amount of dry air to the west and north is visible on water vapor satellite loops, and this dry air is interfering with TD 7's heavy thunderstorms. Wind shear is a light 5 - 10 knots, which is quite favorable for intensification. Ocean temperatures are 26°C, which is a bit on the cool side, though. Winds at the Middle Atlantic buoy 41041 were 20 mph at 5 pm EDT, and should rise this evening, as the center of TD 7 passes about 50 miles to the south near midnight. The first hurricane hunter mission into TD 7 is scheduled for Saturday morning.
Figure 1. Satellite image of TD 7 as it was forming at 3:17 pm EDT August 9, 2012.
Forecast for TD 7
TD 7 formed about 400 miles east-northeast of where Ernesto became a tropical depression, as seen on our wundermap. Atmospheric and oceanic conditions are currently quite similar to what Ernesto experienced, and I expect TD 7 will struggle with dry air like Ernesto did. The SHIPS model predicts that shear will remain light through Friday then rise to the moderate range on Saturday, when the storm will encounter moderate shear from upper-level westerly winds associated with a trough of low pressure. Since conditions are so similar to what Ernesto experienced, the official NHC forecast of a 45 - 50 mph tropical storm moving through the Lesser Antilles Islands Saturday and Sunday is a reasonable one.