Andrea Intensifies to a 60 mph Tropical Storm, Spawns 5 Tornadoes in Florida

Tropical Storm Andrea has exceeded expectations. An Air Force hurricane hunter plane flying through Andrea near 3 am EDT found that a strong band of heavy thunderstorms with moderate turbulence and intense lightning had wrapped partway around the center, and Andrea had intensified into a respectable tropical storm with 60 mph sustained winds and a central pressure of 997 mb. The intensification occurred despite the presence of a large area of dry air to the storm's west, and high wind shear of 25 knots. Satellite loops show that Andrea has expanded in size this morning, and its heavy thunderstorms have become more intense. The heaviest thunderstorms were in a band well away from the center, extending from Tampa southwestwards over the Gulf of Mexico. There is a large slot of dry air behind this band, and Andrea may be able to close this intrusion of dry air off early this afternoon, and build additional heavy thunderstorms near its center. However, given the continued presence of dry air and increasing wind shear, and little time before landfall, it will be difficult for Andrea to reach hurricane strength before landfall occurs early this evening--though I won't rule out intensification to a 70 mph tropical storm. Heavy rains of 3 - 6" that have the potential to cause flash flooding will be the storm's main threat. Carrabelle, near Apalachicola, reported 4.5" of rain in a 5-hour period ending at 8 am EDT. Tornadoes in some of the heavier thunderstorms in Andrea's spiral bands are also a concern, and the storm had already spawned five tornadoes as of 9 am EDT. Bands of heavy thunderstorms with embedded rotating thunderstorms capable of generating tornadoes where over both the west and east coasts of Florida between 6 am - 8am, triggering tornado warnings in the counties near Fort Lauderdale and Tampa Bay. A tornado hit The Acreage in Palm Beach County at 6:45 am EDT, injuring one person, damaging homes, and downing trees and power lines. Two other tornadoes were reported on Florida's east coast, one in Broward County, and one in Palm Beach County. Andrea also spawned two tornadoes southeast of Tampa Bay between 2:30 am and 4 am EDT Thursday, but damage was minor. Most of South and Central Florida are under a tornado watch today. A storm surge of 2 - 5 feet is predicted for Tampa Bay northward to Apalachicola, and rip currents will be a risk for swimmers who brave the high surf. As of 9 am EDT Thursday, our wundermap with the storm surge layer turned on was showing storm surge levels just over 1 foot near Tampa and Apalachicola on Florida's Gulf Coast.

We won't have any new wind measurements from the Hurricane Hunters until about 3 pm EDT. Buoy 42036, 122 miles west-northwest of Tampa, reported sustained winds of 40 mph, gusting to 51 mph, between 7 am - 8 am EDT, when the center of Andrea was located about 60 miles to the south-southwest. Winds at a personal weather station at Bald Point State Park near Apalachicola hit 39 mph at 9 am EDT. Winds at Cedar Key were sustained at 28 mph, gusting to 34 mph, at 8:33 am EDT.



Figure 1. Composite radar reflectivity image of Tropical Storm Andrea at 9 am EDT Thursday, June 6, 2013.

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