Will tropical storm Karen dump heavy rain on Washington, D.C.?

Tropical storm Karen has nearly reached hurricane strength in the southern Gulf of Mexico and should move inland along the northern Gulf coast Saturday. Then, it will hook up with a cold front and head up the East Coast.


Animation of Tropical Storm Karen this morning (NOAA)

Heavy rain is likely to accompany Karen as it rides northward, but the exact track is still a wild card, and will determine whether or not Washington, D.C. receives substantial rain.

Here are the various track forecasts from the available suite of computer models.  Most bring Karen or its remnants fairly close to the D.C. area.


(UCAR)

The GFS model from this morning, shown below, projects Karen would pass very close to the region and produce significant rains.


GFS model simulation of Karen (WeatherBell.com)

But – just to show you how delicate this forecast is – look at an earlier simulation from the same model (from late last night).  It projects the heaviest rain to miss D.C. to the east over the Chesapeake Bay and Delmarva on its closest approach late Monday.


GFS model simulation of Karen (WeatherBell.com)

The Hurricane Center’s track includes a large “cone of uncertainty” – allowing for possible tracks as far west as the Ohio Valley and as far east as offshore the Delmarva Peninsula.


5-day track forecast as of 11 a.m. (National Hurricane Center)

Considering the available information, I’d say the D.C. area has a 50 percent chance of significant rain from this system, of at least one inch.

Here are some rainfall probabilities:

Less than 1″: 50 percent chance

1-2″: 30 percent chance

2″ or more: 20 percent chance

Rain could begin as early as Sunday evening and end as late as Tuesday morning, although I do not expect rain in this entire period and will narrow the timing into a narrower window in future updates.  I do not expect this to be a prolonged heavy rain event.

Given the recent abnormally dry pattern (two-month rainfall deficit of several inches) – meaningful rain would be welcome.


U.S. Drought Monitor as of Wednesday, September 25.

If Karen falls apart (a possibility as it encounters strong wind shear and dry air) or misses the D.C. area, we would probably still receive some showers with the cold front moving through on Monday – but amounts would be modest.

At the moment, strong winds from Karen are not a big concern, as they should die down by the time the storm reaches our area.  But, there’s a small possibility some gusty winds could occur east of its center (perhaps along the tidal Potomac and Chesapeake Bay if the storm tracks close to Washington).

Stay tuned for daily updates on the progress of this storm system.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Brian McNoldy · October 3, 2013