Florida poised for a substantial soaking

An area of showers and thunderstorms is over the southeastern Bahamas and eastern Cuba, in association with a trough of low pressure. The latest 00Z and 06Z runs of the GFS, UKMET, NOGAPS, and ECMWF global dynamical computer models continue to forecast that this disturbance will develop into an extratropical low by Tuesday. The low should bring heavy rain and possible flooding problems to Florida and the Bahamas this week as it lifts northwestward over Florida. Up to nine inches of rain may fall over Florida by Friday (Figure 1), thanks also to a cold front expected to move over the state over the next two days. The exact timing and location of the rains over Florida are still uncertain, as the GFS model predicts development of the low over the Bahamas, while the ECMWF and UKMET models predict development over South Florida. At present, it appears wind shear will be too high to allow the extratropical storm to transition into a subtropical or tropical storm. However, if the storm's center emerges into the northern Gulf of Mexico late this week, wind shear may be low enough to allow a transition to a subtropical storm (10% chance).

Florida could use the rain--most of South Florida is under extreme drought, and Central Florida is under severe drought. The Lake Okeechobee water level is at 10.58 feet (Figure 2), which is about 3 feet below average. During the past week, the lake fell below the level that triggers water conservation measures for the first time since Tropical Storm Fay filled up the lake in August.


Figure 1. Forecast precipitation amount between 8am EDT Monday 5/18/09 and 8am EDT Saturday 5/23/09. Image credit: NOAA/HPC.


Figure 2. Water levels in Florida's Lake Okeechobee were under the level that triggers conservation measures between January 2007 - August 2008. Tropical Storm Fay then filled up the lake, which has gradually declined in level since, reaching water shortage management levels again in May 2009. Image credit: U.S. Army Corps of Engineers.

There has been little change to the large upper-level cold low spinning in the mid-Atlantic a few hundred miles east of Bermuda. The low may spin in place long enough over the next week to develop a warm core and be classified as a subtropical storm. It is unlikely that a subtropical storm forming that far out in the Atlantic this early in the year would pose a threat to any land areas, with the possible exception of Bermuda.

Climatology of early-season Atlantic tropical cyclones
Tropical storms are uncommon in the Atlantic before June 1, with only 26 named storms on record between 1851 - 2008. Five of these have made it to hurricane strength, and only one--Hurricane Able of 1951--made it to major hurricane status. Last year's Tropical Storm Arthur may be the deadliest May tropical cyclone on record. Though only a 40 mph tropical storm at landfall, Arthur killed five people in Belize and caused $78 million in damage. Three early-season storms have brought hurricane-force winds to land. The March 1908 hurricane swept through the northern Lesser Antilles Islands as a Category 1 or 2 hurricane, destroying at least 24 boats and causing damage to buildings on St. Bartholomew. Hurricane Able of 1951 brought sustained winds of 90 - 95 mph to the northern Bahama Islands, but caused little damage. Hurricane 2 of May 1908 hit North Carolina's Outer Banks as a Category 1 hurricane, but also caused little damage.

List of all early season (formed in January - May) Atlantic named storms
May 31, 2008: Tropical Storm Arthur
May 6, 2007: Subtropical Storm Andrea
April 18, 2003: Tropical Storm Ana
April 21, 1992: Subtropical Storm 1
May 6, 1981: Tropical Storm Arlene
January 18, 1978: Subtropical Storm 1
May 21, 1976: Subtropical Storm 1
May 23, 1972: Subtropical Storm Alpha
May 17, 1970: Hurricane Alma (Category 1)
May 28, 1959: Tropical Storm Arlene
February 2, 1953: Tropical Storm Alice
May 25, 1952: Tropical Storm 1
May 15, 1951: Hurricane Able (Category 3)
May 22, 1948: Tropical Storm 1
May 19, 1940: Tropical Storm 1
May 27, 1934: Tropical Storm 1
May 14, 1933: Tropical Storm 1
May 5, 1932: Tropical Storm 1
May 13, 1916: Tropical Storm 1
May 24, 1908: Hurricane 2 (Category 1)
March 6, 1908: Hurricane 1 (Category 2)
May 27, 1890: Tropical Storm 1
May 16, 1889: Hurricane 1 (Category 1)
May 17, 1887: Tropical Storm 2
May 15, 1887: Tropical Storm 1
May 30, 1865: Tropical Storm 1

I'll have an update Tuesday.

Jeff Masters