Thursday, August 31, 2006

DC Braces for Heavy Rain Event;
Ernesto Strengthens Approaching Carolinas


Cloudy, cool. As Tropical Storm Ernesto nears the Carolina coast, a Flash Flood Watch is in effect through late Friday night for most of Maryland, DC, central and northern Virginia, and the eastern panhandle of West Virginia. Click on your county above for details. A state of emergency has been declared for the state of Virginia to allow deployment of the National Guard and other resources. For the latest satellite/radar loop from WUSA-TV9, click here.
[Note that the hurricance "warning" in the WaPo article linked above is bogus as of post time; it is in fact a watch.]

Those clouds you're seeing this afternoon are from a frontal system that stretches through the Carolinas, but radar and satellite images show the beginnings of a merger between that system and the outer fringes of Ernesto to the south. Temperatures are generally between 70° and 75° throughout the metro region this afternoon. The relatively drier northeasterly wind over the Mid Atlantic area has kept precipitation today confined mainly to southern Virginia southward.

Tonight and Tomorrow

Ernesto's rain and wind arrives. Tonight will be cloudy and cool with an increasing breeze, lows in the low to mid 60s, and a 40% chance of a few scattered showers through midnight. By morning, the chance of showers increases to 70% and with more coverage. Rain will be steadier and heavier during the day tomorrow with a chance of some thunderstorms and winds in the 15-25mph range. Highs will be in the upper 60s to near 70. In his post below, Josh has more details on the possible timeline for Ernesto impacts on the metro area, as well as the forecast through the holiday weekend and next week.

Tropical Topics

Ernesto regained strength over the Atlantic overnight and was a strong tropical storm with maximum winds of 70 mph by early this afternoon. It remained at that strength at the 5pm advisory. The storm is headed for landfall tonight near the North Carolina/South Carolina border. As it moves northward, the track will be deflected to the west by a strong high pressure area now centered in eastern Canada. This will also slow down the forward progress of the storm and enhance the precipitation in some parts of the Mid Atlantic area. Paradoxically, it's the relative weakness of the storm which will help increase precipitation amounts by preventing it from barreling off to the north as stronger tropical systems frequently do when they reach middle latitudes.

There is still some disagreement between models on the placement of the heaviest precipitation. The global model from this morning has the precipitation bullseye near the mouth of the Chesapeake Bay, but this afternoon's North American model puts the heaviest amounts from central Virginia to eastern North Carolina with a very sharp cutoff to the northeast. This model has amounts generally less than an inch through Saturday night north and east of the Potomac.

Stay tuned to's continuing coverage of this developing event.

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