Irene at 3 p.m. (NOAA)

It has become clear that areas from the tidewater of Virginia northeast across the Chesapeake Bay to the Delmarva coast will experience a very serious hurricane in Irene. Ocean City residents have been ordered to evacuate and the mayor has declared a state of emergency as Hurricane Irene approaches

As you go west of the Bay, the impacts from Irene are likely to lessen. Determining exactly where the cutoff occurs is a difficult issue. And, as we’ve been stressing, changes in the storm track can have important changes - shifting major impacts east or west.

Right now, here is our best bet of what to expect -subject to change:

The European model - which takes Irene on a westerly track - projects heavy rain briefly reaching even D.C.’s far western suburbs early Sunday morning. (

Fairfax, Montgomery, Prince William, Stafford and Howard counties and the District : Showers likely developing Saturday midday to afternoon. Periods of rain, possibly heavy Saturday night, mainly after 8 p.m. Winds increase to 20-40 mph with possible 50 mph gusts. Rain ends by late Sunday morning. Rainfall potential: 0.5-2”, possibly up to 4” in some locations. Minor to moderate flooding possible in tidal Potomac, especially north facing shores.

Video briefing from Dr. Greg Postel

Prince George’s, Charles, Calvert, Anne Arundel and St. Mary’s county : Showers developing Saturday late morning to midday becoming heavy south to north late in the afternoon and evening. Heavy rain squalls at night, possible flooding. Winds increasing as high as 30-60 mph - strongest near the Bay, possible power outages. Rain ends by midday Sunday. Rainfall totals 2-6” - highest amounts near the Bay. Moderate to major tidal flooding possible, especially north facing shores.

Virginia tidewater and Delmarva Peninsula

Strong tropical storm or hurricane conditions likely. Rain developing Saturday morning and becoming heavy during the afternoon. Heavy rain and damaging winds Saturday night. Winds increasing to 40-70 mph, with gusts as high as 90-100 mph on the ocean with widespread power outages. Extremely dangerous storm surge possible for the beaches of up 4-8 feet, causing extensive flooding. Rain ends Sunday morning. Rainfall totals of 6-10” possible - causing inland flooding, isolated higher amounts.

Tomorrow we will create detailed maps to better visualize this.