Subtropical Storm Andrea was the first named storm of the 2007 Atlantic hurricane season. Andrea developed on May 9 from a previously extratropical low pressure system while located about 150 miles northeast of Daytona Beach, Florida. Andrea weakened to a subtropical depression on May 10 as vertical wind shear and dry air entrainment took their toll. Andrea dissipated on May 11, with its remnants generating sporadic bursts of deep convection. Andrea was the eighth earliest storm on record to form in the Atlantic basin, and the first May storm since Arlene in 1981. In addition, Andrea was the first pre-season storm to develop in the Atlantic since Ana in 2003.
Andrea caused only minimal damage, but caused 6 fatalities, all direct.
|Formation||May 9, 2007|
|Dissipation||May 11, 2007|
|Highest winds||60 mph|
|Lowest pressure||1001 mbar|
|Areas affected||Virginia, North Carolina, South Carolina, Georgia, Florida, Bahamas|
|Part of the||2007 Atlantic hurricane season|
The precursor to Andrea was an extratropical cyclone that developed just offshore the mid-Atlantic coast on May 6. The extratropical cyclone steadily strengthened that day, with the pressure dropping 16 mb in a 24-hour period ending 0600 UTC May 7. Initially, the cyclone possessed the classic signature of a fully matured extratropical cyclone, with the associated cold front pushing through Florida and reaching as far south as Cuba on May 7. By late on May 7, the extratropical cyclone lost most of its baroclinic support, and, as a result, ceased strengthening. However, interaction of the extratropical low as well as the strong high pressure area to the north, produced hurricane force winds. The resulting area of hurricane force winds, along with the slow movement of the extratropical cyclone, produced large waves that impacted much of the southeastern United States as well as the Bahamas. On May 8, the extratropical low weakened and began drifting to the west over warmer waters in the western Atlantic Ocean. As the low moved west, upper-level wind shear decreased, which allowed the cyclone to generate deep convection closer to the circulation center. By early on May 9, convection had become symmetric around the cyclone's low-level circulation center. In addition, the cyclone lost all of its frontal structure as well as its cold core structure, and the wind field contracted. Based on this, it is estimated that the low developed into Subtropical Storm Andrea at 0600 UTC May 9 while located about 150 miles east of Jacksonville, Florida.
Upon formation, Andrea had already reached its peak intensity of 60 mph, since the cyclone would later weaken. Initially, Andrea was trapped within the retrogating mid- to upper-level cutoff low that had caused the pre-Andrea extratropical cyclogenesis. This pattern caused Andrea to be embedded within an environment of low vertical wind shear, and it also caused the cyclone to drift slowly to the west. By late on May 9, Andrea came under the influence of strong northerly flow aloft on the western side of the upper-level low, which caused an increase in shearing and displaced the deepest convection southeast of the low-level circulation center. By 1200 UTC May 10, Andrea weakened to a subtropical depression while located about 95 miles east-southeast of Jacksonville, Florida. Devoid of deep convection, Andrea degenerated into a remnant low by 0000 UTC May 11. Andrea's remnants produced intermittent bursts of deep convection on May 11 while drifting southward just offshore the central Florida coast. This convection was transient and was never persistent enough for Andrea to redevelop. On May 12 and 13, Andrea's remnants accelerated to the northeast ahead of an approaching cold front. By May 14, Andrea's remnants were absorbed by the aforementioned cold front.
Because of the high surf from the precursor disturbance to Andrea, the National Weather Service issued a High Surf Advisory for much of the southeast and east coast from Florida to North Carolina. When Andrea developed into a subtropical cyclone, the National Hurricane Center issued a Tropical Storm Watch from the mouth of the Altamaha River in Georgia to Flagler Beach, Florida. Once Andrea weakened to a subtropical depression, the watch was discontinued. In addition to the aforementioned watches/warnings, a gale warning was issued for much of the South Carolina coast.
At Isle of Palms in South Carolina, workers as well as dozens of firefighters prepared sandbags in order to prepare for high tide after the waves of Andrea previously caused moderate beach erosion. As a precaution, officials there cut power and gas to numerous uninhabited buildings. Also, officials closed schools in Dare County, North Carolina due to the threat of high winds from Andrea. The North Carolina Department of Transportation cancelled ferry transportation to and from Ocracoke and Knotts Island, North Carolina.
Prior to developing into a subtropical cyclone, Andrea produced gale force winds as well as high surf along the coast from North Carolina to Georgia, and later on, along the coasts of Florida and the Bahamas. The waves caused beach erosion and washed up against a coastal house located along the southeastern coast of the United States.
In Virginia, Andrea produced winds of 52 mph in Norfolk, with an unofficial report of 57 mph winds near Virginia Beach.
Andrea produced 34 foot waves offshore the coast of North Carolina. In addition, the cyclone produced tropical storm force winds. The waves and winds damaged three boats; the 9 passengers from all three ships were later rescued by the Coast Guard. All nine people were injured to an extent; three had hypothermia, one had a broken rib, and one Coast Guardsmen experienced back injuries from the high surf produced by Subtropical Storm Andrea. Also, another boat along with its four occupants were reported missing. Winds of 50+ mph occured along the Outer Banks, with the winds knocking some tree limbs onto power lines and causing some isolated power outages. Wind damage included roofs losing shingles. In Elizabeth City, one of Andrea's rainbands dropped 0.5 inches of rain in about 2 hours, and that band also produced some lightning strikes; one bolt injured two firefighters. Strong winds associated with Andrea covered portions of North Carolina Highway 12 with sand, and the route was closed for a day after waves from Andrea washed out about 200 feet of the road. In some areas, Andrea's waves eroded up to 20 feet of beach, leaving 70 homes in imminent danger.
High waves from the precursor disturbance left two kayakers missing near Seabrook Island, South Carolina. One was found the next day, and the other was found dead a week later.
On St. Simons Island, Georgia, Andrea a storm surge of 8.09 feet. In addition, Andrea produced traces of rainfall in the southeastern portion of the state.
In Florida, Andrea produced waves of over 10 feet, which capsized a boat near Lantana; the boat's two occupants were rescued without injury. In addition, the waves displaced a sailboat that had previously been washed ashore near Juno Beach. High waves caused a parking lot to flood and destroyed several fences and tree branches at Jupiter Beach, which caused its temporary closure. Also, a maintenance shed that was nearby was destroyed by the storm. Eight Leatherback Sea Turtle nests in Boca Raton were destroyed after the surf reached the dunes. Because of the high surf from Andrea, the pier at Flagler Beach was closed for about a day. Minor to moderate beach erosion caused the Florida Department of Transportation to fill in areas near the seawall with sand. One person was killed when he drowned in the rough surf off the coast at New Smyrna Beach. Andrea's outer rainbands produced light rainfall across Florida, with the highest report being reported in Jacksonville, where it reached 0.77 inches. In addition, the bands produced tropical storm force wind gusts across the northeastern portion of the state. The strong winds spread smoke from local brush fires through the Tampa Bay area and into Miami. High winds from Andrea were reported as fueling severe wildfires in northern Florida and southern Georgia.