Three tropical systems to watch

The tropics are getting more interesting today, with three systems to discuss. None of these systems poses a significant threat to any land areas, with the possible exception of Bermuda, for the last system I'll discuss.

Firstly, the low pressure system northeast of the Bahama Islands remains very disorganized today. The dry air to its west has been inhibiting its growth, despite the presence of relatively modest wind shear of 5 - 10 knots overhead. The wind shear is coming from the west, which is driving the dry air over Florida into the heart of the storm's circulation. If the wind shear had been from the opposite direction, where there is less dry air, the storm would have had a better chance of coming together. The system appears as a blob of clouds with just a few areas of deep thunderstorms, rotating about a broad and ill-defined center.


Figure 1. Preliminary model tracks for the Bahamas blob.

The Hurricane Hunter aircraft scheduled to investigate the system today has been cancelled, but is scheduled to fly on Sunday if needed. The system still has the potential to organize into a tropical depression, but its window of opportunity it getting short. The system should make landfall by Sunday or Monday along the northern Florida, Georgia, or South Carolina coast and dissipate inland. The dry air will continue to be a problem for the storm today, but may get diluted enough Sunday to allow some organization to occur.


Figure 2. Visible satellite image of the three tropical disurbances to watch today.

Low 800 miles east of Bermuda
A second area to watch is a well-defined area of low pressure far out in the Atlantic at 34N 51W, about 800 miles east of Bermuda. There is deep thunderstorm activty completely surrounding the low, and QuikScat satellite wind estimates showed winds near tropical depression strength--in the 20 - 30 mph range--at 4:30 am EDT this morning. However, sea surface temperatures (SSTs) are in the 23-25 C range, which is below the 26 C threshhold usually needed for tropical storm formation. This low reminds me of the "Greek" storms Delta, Epsilon, and Zeta that formed in a similar location with similar SSTs last Fall. Today's storm may be able to spend enough time the next few days over waters just warm enough to allow it to make the transition to a subtropical storm and perhaps even a tropical storm. The system is not a threat to land right now, and will track westward towards Bermuda over the next few days.


Figure 3. Preliminary model tracks for the low 800 miles east of Bermuda.

Forecasted development north of Puerto Rico
Most of the global computer forecast models--with the notable exception of the UKMET model--have been consistently forecasting a tropical or non-tropical storm to form northeast of Puerto Rico on Tuesday or Wednesday. Today is the third day in a row the models been making this forecast, so I thought I'd finally mention it, despite my doubts about the liklihood of this happening. There is a lot of wind shear forecast to be in the vicinity of the forecasted low, so it may have a difficult time organizing into a tropical storm. If a storm does form here, it is forecast to move northward and threaten Bermuda late next week. SSTs are in the 26 - 28 C range in the area, which is warm enough to support a tropical storm.

I'll be back with up update on Sunday, unless there is a major development to discuss.

Jeff Masters