High wind shear dominates the Atlantic

There are two areas of heavy thunderstorms over the Atlantic worth mentioning today. One area, over the southern Gulf of Mexico, is under 20-30 knots of vertical wind shear (Figure 1). Wind shear is expected to increase to very high levels over the Gulf over the next week (Figure 2), and there will be no tropical development there. The second area is between the Bahamas and Bermuda. Wind shear is also a high 20-30 knots in this region, and is expected to remain at about this level over the next few days. QuikSCAT imagery from this morning shows some winds of tropical storm strength, but no evidence of a surface circulation or even a wind shift in this area. Some of the computer models are forecasting that a low pressure system will develop in this area sometime in the next week, but it appears that this low will probably be extratropical.

Next week, we'll have to keep an eye on the Caribbean. Wind shear is expected to drop to low levels (Figure 2), and any tropical waves or cold fronts that move into the region might have the potential to develop. However, I'm not expecting any development.

Figure 1. Wind shear from 8am EDT today, as forecast by last night's 00Z (8pm EDT) GFS model run. The red areas show areas less than 16 knots of wind shear, which are favorable for tropical storm formation. The wind units are in meters per second; a rough rule of thumb is that 1 m/s = 2 knots. The high levels of wind shear over most of the tropical Atlantic is typical of what we see in October during an El Nino year.


Figure 2. Seven-day wind shear forecast for 8am EDT Wed October 11, as forecast by last night's 00Z (8pm EDT) GFS model run. The red areas show areas less than 16 knots of wind shear, which are favorable for tropical storm formation. The wind units are in meters per second; a rough rule of thumb is that 1 m/s = 2 knots. While most of the tropical Atlantic is expected to be under high wind shear, a "hole" in the shear is expected to open over the Caribbean.

Jeff Masters