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Tropical Depression Five struggling

By: Dr. Jeff Masters, 8:13 PM GMT on August 11, 2010

Tropical Depression Five is in serious decline, thanks to an unexpected increase of wind shear to about 20 knots this afternoon. Long range radar out of the Florida Panhandle shows a fair amount of heavy thunderstorm activity, but little organization into low-level rain bands. TD 5 has brought up to two inches of rain to the New Orleans region. The Hurricane Hunters have just left TD 5, and they found no well-defined surface circulation, a pressure that had risen since this morning's flight, and top winds of just 30 mph. It is questionable whether TD 5 really was a tropical depression for much of the day. Recent satellite images suggest that the center of the storm has relocated near some of the heavier thunderstorms, about 60 miles southeast of the Alabama/Mississippi border. If this new center does indeed become stable, TD 5 will move ashore in the warning area tonight or early Thursday morning, before the depression can develop into a tropical storm. TD 5 is still capable of dropping heavy rains of 3 - 5 inches along its path, however, since the storm is expected to slow down after landfall.

Figure 1. Afternoon radar image of TD Five from the Florida Panhandle radar.

The tropical wave (Invest 93) in the middle Atlantic Ocean that has been close to tropical depression status for three days has suffered a setback today, as dry air driven into the core of the storm by strong upper-level winds disrupted the circulation. The disturbance still has a well-defined surface circulation, but only a very limited amount of heavy thunderstorm activity. Wind shear is expected to stay in the moderate range, 10 - 20 knots, over the next three days, which is low enough that 93L could become a tropical depression at any time during that period. NHC is giving 93L a 50% chance of developing into a tropical depression by Friday afternoon. A strong trough of low pressure moving across the central Atlantic is recurving 93L to the north, and the system should only be a concern to shipping interests.

Moscow's air clears, but it is still extraordinarily hot
A thunderstorm blew through Moscow early this morning, bringing a little rain and a very welcome shift of wind direction. The wind shift freed the city from the persistent wild fire smoke that had plagued the city for seven straight days. Temperatures at Moscow's Domodedovo airport hit 35°C (95°F) today, the 29th day in row that temperatures have exceeded 30°C (86°F) in Moscow. The average high temperature for August 11 is 21°C (69°F). Moscow's high temperatures have averaged 15°C (27°F) above average for the first eleven days of August--a truly extraordinary anomaly. There is some modest relief in sight--the latest forecast for Moscow calls for high temperatures of 30 - 31° (86 - 88°F) Thursday through Sunday. This is still 20°F above normal, but will be a welcome change from the extreme heat of the past two weeks. Long range forecasts from the ECMWF and GFS models show no major change to the ridge of high pressure locked in over Russia, for at least the next seven days. However, both models suggest that a trough of low pressure may be able to erode the ridge significantly 8 - 10 days from now, bringing cooler temperatures of 5°C (8°F) above average.

Next update
I'll have an update Thursday morning.

Jeff Masters


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