Tropical Storm Colin
Tropical Storm Colin has made its debut over the Atlantic, but does not appear to be a threat to any land areas over the next five days. Satellite imagery shows that Colin is intensifying, as both the intensity and areal extent of heavy thunderstorms has increased over the past few hours. A respectable low-level spiral band is developing to the north of the center, and upper-level outflow is beginning to appear on all sides of the storm. Colin is a very small storm, and its tropical storm force winds extend out just 30 miles from the center. Colin passed about 50 miles south of Buoy 41041 early this morning, and generated top sustained winds of 27 mph at the buoy. There is some dry air associated with the Saharan Air Layer (SAL) to the northwest of Colin, but this dry air is not getting entrained into Colin at present. Wind shear is a low 5 - 10 knots and sea surface temperatures are a very warm 28 - 29°C, so continued development is likely today. The main negative for development appears to be the storm's small size, which makes it vulnerable to modest increases in wind shear or dry air entrainment. The first flight of the Hurricane Hunters into Colin is scheduled for Wednesday morning.
Forecast for Colin
The latest 6Z (2am EDT) models are fairly unified taking Colin to the west-northwest at 20 - 25 mph for the next three days. This would bring squalls from the storm's outer rainbands to the northern Lesser Antilles Islands, such as Antigua and Barbuda, by Wednesday afternoon. The center of Colin should pass to the northeast of the islands, and the storm is small enough that the islands are unlikely to experience tropical storm force winds. As Colin makes its closest approach to the Lesser Antilles on Wednesday night, the storm will begin to encounter strong upper-level westerly winds associated with the counter-clockwise flow of air around an upper-level low pressure system centered between Bermuda and Puerto Rico. The latest SHIPS model forecast predicts that these winds will cause wind shear to rise to the moderate level, 10 - 20 knots, by Wednesday morning, and to the high level, 20 - 30 knots, by Thursday. There is considerable dry air associated with the upper level low that should cause problems for Colin, as well. The high wind shear and dry air should weaken Colin. NHC is giving Colin a 25% chance of attaining hurricane status this week.
A trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough will pull Colin to the northwest and cause it to slow down on Wednesday. By Friday, Colin will be moving at half of its current speed. It is unclear if the trough of low pressure will be strong enough to fully recurve Colin out to sea late this week. Some of the models predict Colin will not recurve out to sea, and that high pressure will build back in this weekend, forcing Colin towards the U.S. East Coast. A second trough of low pressure is predicted to move off the U.S. East Coast next Monday, so Colin will have a second opportunity to recurve out to sea then. It is possible that Colin could make landfall along the U.S. East Coast or in the Canadian Maritime provinces 7 - 10 days from now, though it is still too early to assess the risk of this happening, nor how strong Colin might be.