Support Our Work
A look at weather extremes and the big-picture climate connections.

Tropical Storm Debby Threatens Gulf Coast

Tropical Storm Debby formed in the Gulf of Mexico on Saturday, and now threatens a broad area of the U.S. Gulf Coast, particularly the Panhandle of Florida, southern Alabama, and Southeast Louisiana. Debby is the earliest “D” storm on record in the North Atlantic Basin, marking an extraordinary start to the 2012 hurricane season. Typically the fourth-named storm of the season forms in mid-to-late August, and the previous record-holder was Hurricane Dennis, which formed on July 5, 2005.  

Tropical Storm Debby has gained strength since Saturday, and had maximum sustained winds of 60 miles per hour as of Sunday morning (check the National Hurricane Center's website for the latest advisory info). The strongest winds have been displaced well east of the center of circulation, however, which is an indication that the storm is still somewhat disorganized.

Infrared satellite image of Tropical Storm Debby on Sunday, June 24. Click on image for a larger version. Credit: NOAA.

The main threat so far comes in the form of heavy rainfall. Although the heaviest rain has stayed offshore, the region that is most likely to experience 5- to 10-inch rainfall amounts is the same area that was hard hit by flash flooding earlier in June — coastal Alabama and the Florida Panhandle. There is also a threat of tornadoes on the eastern side of the storm, which has put Florida on alert throughout much of the weekend.

Debby has prompted tropical storm watches and warnings from the coast of Louisiana (not including New Orleans or Lake Pontchartrain), eastward to Anclote Key, Fla. Such a warning means that tropical storm conditions are expected within 36 hours. Already, tropical storm force winds are being reported near the Florida coast, with a buoy near Apalachicola, Fla., reporting wind gusts to 48 mph on Sunday afternoon. For more buoy observations during the storm, head to the website of NOAA's National Buoy Data Center.

The storm is in an area with weak steering currents in the atmosphere, which essentially means that it’s drifting around, unsure of where it’s ultimately headed. Initial forecasts had Debby making a westerly turn and making landfall, possibly as a hurricane, in Texas early in the week. Now the National Hurricane Center has significantly revised that forecast, bringing the storm ashore in southeastern Louisiana.

National Weather Service graphic showing the threats to several Gulf Coast states. Click on image for a larger version.

Forecasters have cautioned that this is a very low confidence short-term forecast, which contrasts with the improved track forecast skill seen during the past two decades. This statement from the NHC on Sunday morning sums up the situation: “IT IS A VERY DIFFICULT AND HIGHLY UNCERTAIN FORECAST THIS MORNING.”

The Hurricane Center’s forecast call for some additional strengthening, and Debby could become a hurricane before making landfall, although it is currently being impeded by wind shear and dry air that is giving the storm a lopsided appearance on satellite images.

Here is more from the NHC’s 10 a.m. discussion. I've added notations in brackets, and one sentence is bolded for emphasis:

“GIVEN THE WESTWARD TURN INHERITED FROM THE PREVIOUS FORECAST . . . AS WELL AS THE HISTORICAL STRONG RECORD OF THE ECMWF [a medium-range computer model] . . . THE NEW OFFICIAL FORECAST MOVES DEBBY INITIALLY A LITTLE BIT TO THE NORTHEAST TO REFLECT CURRENT TRENDS BUT THEN TURNS THE CYCLONE BACK TOWARD THE WEST OR WEST-NORTHWEST IN 24 TO 36 HOURS.  A MAJORITY OF THE GFS ENSEMBLE [another near to medium-range computer model] MEMBERS NOW ARE CONSISTENT WITH THE DETERMINISTIC RUN . . . WHICH WAS NOT THE CASE YESTERDAY . . . MAKING A STRONGER CASE FOR THE EASTWARD SOLUTION.  WE MUST BE READY TO MAKE A CHANGE OF THE FORECAST TRACK AT ANY TIME.

Computer model projections for the path that Tropical Storm Debby may take, illustrating the forecast uncertainty. Click on image for a larger version. Credit: Weather Underground.

Debby has prompted the shut down and evacuation of some Gulf of Mexico oil drilling platforms, according to the Associated Press. A significant disruption of Gulf oil production would very likely increase U.S. gasoline prices.

« Extreme Planet