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September 2, 2011

Big, wet Gulf storm unlucky for all

Tropical Depression 13 continues to linger off the northern Gulf Coast Friday, with modest winds but formidible rains for the region, and for wherever the storm decides to go next week.

Forecaster expect TD13 to reach tropical storm strength later today, becoming Tropical Storm Lee. Tropical Depression 13For now, it is centered roughly 210 miles southwest of the mouth of the Mississippi River, moving north at 1 mph. Actually, forecasters can't be certain precisely where the storm is centered, where it's headed or how fast it's moving. That's because its center is hard to find, and its movement is both slight and erratic.

UPDATE, 1:45 p.m.: TD13 is now Tropical Storm Lee, with top sustained winds of 40 mph. Forecasters have not ruled out the possibility that Lee will reach hurricane strength. Earlier post resumes below.

The offshore oil rigs are reporting tropical storm winds  north and east of the storm's center, forecasters said. And rain bands are now soaking coastal Louisiana.

What they do know is that it is packing a lot of rain, and is likely to strengthen. There is a Tropical Storm Warning in effect from Pascagoula, Miss. west to Sabine Pass, Texas, including the low-lying city of New Orleans and Lake Pontchartrain. And the warnings predict 10 to 15 inches of rain, with the potential for as much as 20 inches through Sunday before this dawdling rain maker finally leaves.

UPDATE, 12:30 p.m.: Just got off a teleconference call with Bill Read, director of the National Hurricane Center. There was some discussion of whether the New Orleans-area pumps will be able to keep up with the heavy rains that are forecast with this storm. We may be seeing footage of water rising in the streets in that city before TD13 is through.

What really caught my attention were his comments on what happens down the road, when the tropical rains move north and east: "When the storm moves out," he said, "it will bring heavy rain northward into the Appalachians." He pointed to scenes we've seen this week out of Vermont, and said they may be repeated in the Southern Appalachians. "Unfortunately ... that's the kind of terrain where flash flooding is fast and it's violent. The exact timing and locations [of such events] are yet to be seen."

At least TD13 (or Lee) will be "gone before Katia's even in the picture," he said.  

The forecast models are still a mess. But the consensus seems to be that TD13 will approach the coast of southern Louisiana this weekend, then turn gradually toward the northeast.

NWS forecasters in Sterling, Va. are anticipating that "a plume of tropical moisture from what should be named Lee will stream across the mid-Atlantic from the middle of next week into the weekend. This, along with an onshore flow, could create a significant rainfall event for the region."

Meanwhile, out on the high seas, Hurricane Katia has been demoted to a tropical storm.

UPDATE, 11:00 a.m.: Katia has regained minimal hurricane strength, with top sustained winds of 75 mph. 

Wind shear from the south is putting hobbles on the storm's ability to strengthen. But after a few more days that problem is expected to abate, and Katia is likely to restrengthen, forecasters said.

The other issue is Katia's course. Forecasters say the storm is rounding the southwestern rim of a large high-pressure ridge over the mid-Atlantic. That is expected to allow her to curve more to the northwest for a time.

But the consensus seems to be that the ridge will restrengthen farther to the west, turning Katia back to the west-northwest. That means the storm will get back to a course that brings it closer to the U.S. East Coast before turning north.

Then the issue becomes, "How close?"

Here are some of the forecast model tracks for Katia. Here is the latest advisory. Here is the forecast discussion. And here are the NHC forecast track maps.

Posted by Frank Roylance at 10:50 AM | | Comments (0)
Categories: Hurricanes
        

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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff
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