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Posted at 03:06 PM ET, 08/24/2011

Hurricane Irene: what might it mean for Washington, D.C. and nearby beaches?

Hurricane Irene at 2 p.m. (NOAA)
As of 2 p.m., the powerful hurricane Irene was still strengthening over the Southeast Bahamas, with maximum sustained winds up to 120 mph. Additional intensification is likely over the next day or two as it continues towards the East Coast. It may reach the dangerous category four level at some point.

For days, we’ve been vague and non-committal about the potential impacts in the D.C. metro region. The legitimate scientific rationale for that is simply that hurricane track forecast errors are large, especially four and five days into the future.

While uncertainty remains large with respect to Irene’s track, let’s paint a couple possible scenarios of what might happen this weekend both for the D.C. metro region and nearby beaches.

Scenario 1: Storm tracks east of North Carolina Outer Banks due north or north-northeast (favored scenario right now)

Washington D.C.

The GFS model (from this morning) simulates Irene tracking just offshore, bringing heavy rain to the Delmarva Peninsula Saturday night along with very strong onshore winds, while the D.C. metro region just sees showers (
* Partly sunny skies Saturday, with a chance (30%) of intermittent showers developing especially in the afternoon and evening.
* Possible (40% chance) periods of heavy rain showers, gusty winds (20-40 mph) Saturday night. Any rain tapers off during the day Sunday (probably early) and it becomes partly sunny.
* Moderate coastal flooding possible north facing shores of tidal Potomac and Chesapeake Bay.

VA/MD/DE Beaches

* Rain showers very likely develop south to north Saturday, becoming heavy in the afternoon (south) and at night north. Heavy rain showers/squalls continue into Sunday, ending south to north. Several inches of rain possible.
* Winds increase during the afternoon and at night, gusting to tropical storm levels, 35-74 mph.
* Moderate to major coastal flooding, beach erosion, dangerous surf - possible evacuations

Scenario 2: Storm tracks over or slightly west of the Outer Banks and then due north

Washington D.C.

The European model (from this morning) tracks Irene very close to both Outer Banks and Delmarva Peninsula, bringing torrential rain, severe flooding, and damaging winds to the coast - with a period of heavy rain and strong winds into the D.C. metro region mainly Saturday night and Sunday morning. (
* Rain showers likely develop Saturday during the day, becoming heavy at night and lasting into Sunday afternoon. Several inches of rain possible, flash flooding - especially east of I-95.
* Winds increase during the afternoon and especially overnight Saturday into Sunday morning, gusting to tropical storm levels, 35-74 mph. Some power outages possible.
* Moderate to major coastal flooding likely north facing shores of tidal Potomac and Chesapeake Bay.

VA/MD/DE Beaches

* Rain showers develop Saturday south to north, become torrential at times late Saturday and Saturday night, south to north. Heavy rain continues into Sunday, with 4-8” possible and flooding.
* Winds increase Saturday into Saturday night to tropical storm levels (sustained) and possible hurricane-force gusts to 74-100 mph.
* Major to severe coastal flooding, beach erosion, dangerous surf - likely mandatory evacuations.


These two scenarios do NOT represent the full range of possible outcomes. For example, there’s an outside chance the storm could cut farther west than forecast, tracking up the Chesapeake Bay or even over D.C. itself. In that scenario, flooding rain and damaging winds would probably occur over the metro region late Saturday into Sunday, with storm surge flooding along the Tidal Potomac. Impacts at the beaches would be severe, even devastating. There’s also an outside chance the storm passes far enough to the east that D.C. has mainly sunny skies all weekend, and beaches just get a glancing blow.

We’ll update this assessment with more details and greater confidence Thursday and Friday.

By  |  03:06 PM ET, 08/24/2011

Categories:  Latest, Tropical Weather

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