Tropical Storm Andrea Forms in Gulf of Mexico

The Atlantic has its first named storm of the 2013 hurricane season: Tropical Storm Andrea. An Air Force hurricane hunter plane was able to locate a closed center of circulation, and found surface winds of 40 mph in the large area of thunderstorms on the east side of the center. Satellite loops show that Andrea is a lopsided storm. It's center of circulation is exposed to view, due to a large region of dry air that covers the entire Central and Western Gulf of Mexico. This dry air is from a trough of low pressure whose upper level winds are also creating moderate wind shear of 15 - 20 knots over Andrea. Wind shear is forecast to rise to the high range, 20 - 40 knots, by Thursday. Andrea is forecast to make landfall along the northern Gulf Coast of Florida by Thursday evening, so the system has a short window of time to intensify. Given the large amount of dry air to Andrea's west, and the forecast for increasing shear up until landfall, I expect that the strongest sustained winds Andrea could have before landfall are 50 mph. Heavy rains will be the storm's main threat, though a few isolated EF-0 tornadoes will also be possible in some of the heavier thunderstorms in Andrea's spiral bands. A storm surge of 2 - 4 feet is predicted for Tampa Bay northward to Apalachicola, and rip currents will be a risk for swimmers who brave the high surf. Fort Pickens, located in Gulf Islands National Seashore on a barrier island offshore from Pensacola, Florida, has been closed to visitors due to the approaching storm. A single 2-lane road vulnerable to storm surges runs to Fort Pickens. Officials want to prevent a repeat of the situation that occurred in September 2011, when Tropical Storm Lee pushed a storm surge over the road that blocked it with sand and debris, trapping numerous campers and visitors in Fort Pickens. As of 7 pm EDT, our wundermap with the storm surge layer turned on was showing storm surge levels were less than 1 foot along the Florida coast.


Figure 1. MODIS image of Tropical Storm Andrea in its formative stages, taken at 12:20 pm EDT Wednesday, June 5, 2013, five hours before it was named. Image credit: NASA.

Andrea's place in history
Andrea formed in a typical location for early-season storms. The Gulf of Mexico, Western Caribbean, and Bahamas are the usual areas for the genesis of June tropical storms. Andrea's formation date of June 5 is over a month earlier than the average July 9 date for formation of the season's first named storm. On average, the Atlantic sees one June named storm every two years. In 2012, we'd already had two named storms by this point in the season--Alberto and Beryl. This year is the second time a storm named Andrea has appeared in the Atlantic. The previous incarnation, Subtropical Storm Andrea of 2007, wandered off the U.S. East Coast in May, and never made landfall. The 2013 version of Andrea is highly unlikely to get its name retired, and we'll be seeing a third coming of the storm in 2019.

Jeff Masters