Bahamas Blob update

An area of disturbed weather over the Bahama Islands is associated with an upper-level low pressure system. This low is kicking up some strong thunderstorms over the Bahamas and Cuba, but has not improved in organization today. The low is cold-cored, and is making the slow transition to a warm-cored system. It needs to have a warm core in order to develop into a tropical storm. It typically takes three or more days sitting over warm water for this process to happen (let's call today day two of its existence). Wind shear is down to 5-20 knots as of 2pm EDT, which is marginally favorable for development. Water temperatures are very favorable, 28 - 29 C. However, there is little thunderstorm activity near the center of circulation, which is southeast of Key Largo, FL. All the thunderstorm activity is well away from the center, making it unlikely that we'll see a tropical depression today or tomorrow. One of the key signs that a cold-cored system is making the transition to warm-cored is that one has substantial thunderstorm activity near the center of circulation.

The big question is if the center of circulation will be over water or land Thursday and Friday. Right now, it appears that the center is moving north-northwest, and will be over the Florida Peninsula Thursday. Most of the models indicate that the center will continue moving north-northwest, and stay over the Florida Peninsula most of Thursday and Friday. Should the center emerge into the Gulf of Mexico, or remain off the East Coast of Florida, we could see a tropical or subtropical depression by Friday. The low is expected to get picked up by a strong trough of low pressure emerging off the East Coast Friday, then get swept up the coast this weekend. Both the GFS and UKMET models predict that the low will from into a tropical or subtropical depression south of North Carolina by Saturday, and bring tropical storm-force winds to the North Carolina Outer Banks on Saturday and Massachusetts' Cape Cod on Sunday. If you have plans to be either place this weekend, keep a watchful eye on the tropics! This situtation is very similar to what we had at the end of June, when we almost had Tropical Storm Beryl hitting eastern North Carolina.


Figure 1. Current satellite image of the blob of disturbed weather over the Bahamas.

The rest of the tropical Atlantic is quiet today.

Jeff Masters