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Posted at 4:25 PM ET, 11/ 9/2009

Weakening Ida closes in on Gulf Coast

By Greg Postel

Strong winds, flooding still a threat; East Coast impacts?

* Will Ida impact D.C.? Local Forecast | Hurricane Tracking Center *

Radar shows Ida's rains already soaking parts of the Gulf Coast on Monday afternoon. Courtesy National Weather Service.

The first tropical system of the year to realistically threaten the U.S. mainland is poised to make landfall tonight along the Gulf Coast, with the center coming ashore somewhere between eastern Louisiana and the Florida Panhandle. At 4 p.m. EST, the center of Tropical Storm Ida was located about 65 miles southeast of the mouth of the Mississippi River, with maximum sustained winds near 70 mph and tropical storm-force winds (39 to 73 mph) extending outward up to 200 miles from the center.

If this were early September, when the northern Gulf of Mexico waters were 10 degrees Fahrenheit warmer and upper-level winds were more conducive to storm strengthening, this would be big trouble. Fortunately, Ida, downgraded this morning from a Category 1 hurricane, should continue to weaken as it passes across the northern Gulf and encounters water temperatures only in the 70s along with relatively strong winds aloft, which will further disrupt the organization of the storm.

The National Hurricane Center predicts maximum sustained winds only around 60 mph at landfall. Nonetheless, wind gusts to near 70 mph will be possible along the right flank of Ida's circulation center, and flooding rains will likely be a major problem for those in its path. In addition, NHC predicts a storm surge of three to five feet and destructive waves near and to the east of where Ida's center makes landfall.

Already, Ida has spread rainfall into Florida and Alabama and has shut down oil production in the Gulf. Earlier, floods and mudslides caused by Ida killed more than 100 people in El Salvador.

Ida may be weakening, but its remnants could impact areas as far north as New Jersey, including D.C. and the Eastern Shore. Keep reading for more on Ida...

How odd is it to have a land-falling hurricane in November, especially in a November in which El Niño -- the periodic warming of waters in the equatorial Pacific Ocean -- has led to conditions that tend to hinder hurricane development in the Atlantic?

The answer is: very odd. On average in the Atlantic (which includes the Caribbean Sea and Gulf of Mexico) we can expect a November hurricane about once every 5 years. Only four hurricanes, however, have hit the United States in November since 1900, and these were all were Category 1 storms.

The fact that this is an El Niño season makes it all the more unusual that Ida reached hurricane status in the first place. Since 1950, only one tropical system other than Ida has intensified into a hurricane in the Caribbean in an El Niño November.

Probability of tropical-storm force winds (39 mph or greater) between 1 p.m. Monday and 1 p.m. Saturday (EST). Courtesy NOAA.

Fortunately, Ida will lose much of its tropical character by the time it makes landfall early Tuesday. I wouldn't be surprised to see a comma shape in the satellite imagery later today, signaling the evolution away from a tropical cyclone (which has warm air at its center) toward an extratropical cyclone (which has cold air at its center) that more closely resembles a Nor'easter (or, So'easter in this case, I guess).

Forecast models all suggest that the remnants of Ida will move off the Southeast Coast by midweek and merge with a cool front approaching from the Ohio Valley. The combination of systems is expected to create a windy (non-tropical) rainstorm affecting coastal locations from about Jacksonville, Fla., on north to at least around Virginia Beach, Va., during the Tuesday-through-Thursday period.

Depending on the exact track, areas as far north as Atlantic City, N.J., including the Maryland/Delaware Eastern Shore and D.C. area, could see some rain and wind.

See our full forecast for more on potential D.C. area impacts.

By Greg Postel  | November 9, 2009; 4:25 PM ET
Categories:  Tropical Weather  
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