Saturday, August 27, 2011

Updated Hurricane Irene Impacts - Virginia, Maryland, DC Areas...

Hurricane Irene continues to move toward the North/Northeast at about 15 mph, currently located just to the Southwest of Swanquarter, North Carolina.  Maximum sustained winds remain near 85 mph, with gusts around 100 mph  near the center at this time.

The center of Irene will move offshore to the East of the North Carolina/Virginia border later this afternoon.  By early evening the center is expected to be located about 45 miles Northeast of Norfolk.  We'll have to see how much "damage" North Carolina does to the central wind field this afternoon, but I expect Irene to emerge back out to the East of Norfolk with at least 75 mph sustained winds, and then likely pick back up to the 80-85 mph range back out over the water.

Rains are already beginning to spread Northward into the region at this time, as shown by the latest Sterling, VA area radar below:

This trend will continue throughout the afternoon and into this evening, with intensity picking up as well.  Widespread rainfall amounts of 4-6 inches with localized amounts of 8-10 inches can be expected throughout the duration of Irene across the region:

At this time it appears that the bulk of the heaviest rains will take place across the Baltimore/Washington area from about 2pm EDT through 2am EDT.  During that period of time, up to 8 inches of rain may accumulate in some areas.  This will lead to widespread flooding and/or flash flooding in many areas.

As we've feared for days now, the greatest threat from Irene will come in the form of strong, damaging winds that could topple trees and power lines, increasing an already high threat of power outages.  That is indeed what we've seen take place across eastern North Carolina so far today.

The image below shows the expected wind impact from Irene for the duration of the storm:

Specifically for the Baltimore/Washington areas, sustained winds of 30-40 mph with gusts to 50 mph can be expected by late afternoon.  By this evening, susstained winds of 40-50 mph with gusts to 60 mph will be possible (as indicated on the graphic above).  Please keep in mind that these are surface level wind forecasts.  Wind speeds will be 20-30% higher (both sustained and gusts) above the 25th floor of high rise buildings.

The total duration of the maximum winds on the graphic above is expected to range from 5-7 hours at any given location.  Less intense, but still strong, winds will be possible for an additional 3-5 hours in any given location, for a total potential of 8-12 hours of prolonged "wind stress" (i.e., 35+ mph sustained winds with gusts of 45+) across the region.

Storm surge will primarily be a concern along the Southeastern coast of Virginia, where a 7-8 foot rise in water is forecast during the period of high tide this evening:

For the Baltimore/Washington area proper, only minimal water rises are currently forecast, generally in the 1-2 foot range, which could result in minor coastal flooding at the time of high tide this evening.

The main flood related threat to the Baltimore/Washington areas will come in the form of heavy rain and flash flooding.

Isolated tornadoes are also possible in association with Irene.  Tropically-induced tornadoes are typically rather weak and short lived, but can still cause localized damage or injury.

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Shamrock said...

Rob-we had many cars coming thru our roads the last 2 days...people evacuating from Irene from the Carolinas and Virginia It's 1:21 EDT now and it's VERY windy!! I pray for all those in her path. Thanks for your awesome coverage!