Could Hanna Hit D.C. Hard?
Struggling storm downgraded but may recover
The 2008 tropical season, like a gifted quarterback, is spreading the action all over the playing field -- in this case the U.S. Gulf and East Coast. Dolly socked southern Texas, Fay flooded Florida, Gustav engulfed Louisiana, and now Hanna may pound the Southeast Coast. Computer models are almost unanimous in bringing Hanna ashore in Georgia or South Carolina early Friday. Then it will race northward. Depending on Hanna's exact path on its journey north and its intensity, the D.C. metro region may feel a powerful blow.
It should be noted, however, that Hanna is battling powerful wind shear today which is ripping apart its structure. It was recently downgraded to a tropical storm. The shear is forecast to weaken allowing Hanna to recover, but there is a small possibility it will not -- which would all but end the threat of significant impacts along the East Coast.
Keep reading for more on the potential impacts of Hanna on the D.C. area. See also our full forecast through the weekend.
Assuming Hanna survives, it has the potential to be a significant rain producer. Last night, the National Weather Service office in Sterling was bullish about the prospects for meaningful rain:
AT MINIMUM...HANNA WILL BRING RAINFALL TO THE FORECAST AREA BEGINNING SOMETIME FRIDAY AND LINGER THROUGH AT LEAST PART OF THE WEEKEND.
How much rain? NOAA's Hydrometeorological Prediction Center indicates the potential for 4-5" of rain although that number will be highly dependent on the storm's track. If Hanna tracks west of the mountains, the metro area might just experience intermittent showers from the outer bands and less than 2". If the center passes very close to us and we experience torrential downpours associated with the storm's core, some locations could receive more than 5" and flash flooding. Having said that, Hanna will likely be a fast mover, which should limit rainfall amounts to an extent. The exact timing of Hanna's arrival and departure can't yet be pinned down. But early indicators suggest the time of impact may be late Friday into early Saturday.
As for wind, the Sterling NWS was pretty vague:
THE WIND FORECAST IS HIGHLY UNCERTAIN...AND COMPLETELY DEPENDENT ON THE TRACK...TIMING AND INTENSITY OF HANNA.
I'll fill in some detail here. The National Hurricane Center predicts Hanna will come ashore as a Category 1 storm with winds to 85 mph, but as with Gustav and most tropical weather systems, this forecast is highly uncertain. Last night, AccuWeather's Joe Bastardi suggested it could make landfall as a Category 3 storm. Water temperatures are pretty warm off the Southeast coast and wind shear, ripping Hanna apart at present, is forecast to relax as the storm approaches the coast.
Suffice to say, if Hanna strikes South Carolina as a hurricane and races northward through the metro region, we could experience tropical storm winds as in Isabel of 2003.
If the storm tracks well to our west and the center of the storm is over the mountains, we may not experience these strong sustained winds. However, locations east of land-falling hurricanes often experience severe thunderstorms and possible tornadoes embedded within the storm's outer bands. Some of you may recall the when the remnants of Hurricane Ivan spawned a record 40 tornadoes in Virginia in September, 2004.
The other major impact we will need to monitor is the potential for storm surge. If the storm tracks just west of the Chesapeake Bay, a tidal surge may be pushed up the Bay producing a flooding along the shores of the Potomac as in Isabel or the Chesapeake-Potomac hurricane of 1933, which we recently profiled on its 75th anniversary.
Obviously, there are a lot of possibilities with this storm but it does appear to have some potential to have significant impacts on the metro area. There is a chance that it may track far enough west that we dodge the bullet a la Hurricane Hugo in 1993. Or, it could pass far enough east that we only receive a glancing blow a la Gloria in 1985. Or, it may fizzle out and not impact anyone. Time will tell.
We will provide frequent updates as this storm possibly approaches the East Coast in the coming days. Track Hanna, Ike, and several other disturbances using the tracking map below.
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