Special Storm Summary for Florida
David F. Zierden
Florida State Climatologist
Florida State University
Tallahassee, FL 32306-2840
Rare May Storm impacts Florida. While the second half of May usually brings the beginning of Florida’s summer rainy season, characterized by frequent afternoon thundershowers, it is also the month that brings the most stable weather patterns to the State. By late spring the jet stream over North America migrates northward, taking with it the support for strong cold fronts or mid-latitute low pressure systems that impact Florida in the winter and spring seasons. May is also too early in the season to support tropical development, so Floridians can usually count on fairly stable weather outside the threat of routine afternoon thundershowers.
On May 17th and 18th a late season cold front moved across north Florida before stalling across central Florida with its soaking rains. A powerful upper-level and surface low pressure system then formed on this boundary over the southeast Gulf of Mexico. This powerful system was able to tap abundant tropical moisture and brought high winds and soaking rains to Northeast Florida over the next several days. This storm system detached from the primary jet stream shortly after formation, leaving no mechanism to move the system quickly from the area. The storm would be nearly stationary as it pounded the area for several days with high winds and heavy rainfall.
The storm brought unusually powerful winds and surf to Northeast Florida and the Northern Gulf Coast. Persistent easterly wind prompted gale and high surf warnings for the Atlantic Coast and the Northern Gulf of Mexico. Wind-driven waves resulted tides 2-3 feet above normal and water backing up in the St. Johns River and Intercoastal Waterway, where elevated water levels were exacerbated by heavy storm water runoff. Gusts of 51 mph were measured in Daytona Beach and 60 mph at Ponce Inlet. Over 10,000 homes lost power at some point on May 19th or 20th across Central Florida.
In addition the high winds, the storm system also brought widespread heavy rain to nearly all areas of the State with the coastal areas of Northeast Florida once again the epicenter. Virtually all locations, with the exception of the Western Panhandle, have received at least 2 inches of rain from this system with most locations seeing significantly more. Volusia and Flagler counties reported storm totals of over 20 inches thus far, measured by CoCoRaHS volunteer observers (25.49 inches at Ormond Beach) and the Flagler County Fairgrounds (23.75 inces). Even with 9 days left in the month, this May now ranks as the wettest on record (since 1923) at Daytona Beach and the third wettest of any month with a current total of 19.23 inches. Radar derived rainfall estimates shown below highlight the excessive rainfall over Northeast Florida in the last 7 days.
Damage from the system included down powerlines across Central Florida, urban flooding in Volusia and Flagler counties, and minor beach erosion. The hardest hit industry was potato farming in Volusia, Putnam, and Flagler counties. Crops were in the middle of the harvest season and many fields are now under water. Crop damage in the three-county area is estimated at $45 million (source – Orlando Sentinel)
This unusual May storm system is not without benefits, however. Prior to the storm, South Florida had experienced one of its dries “dry seasons” on record (Nov. 1 – April 30). The South Florida Water Management district reported the driest 6-month period since they began keeping records in 1932. The recent rains have eased short-term drought conditions there and Lake Okeechobee is on the rise again at a level of 10.77 ft. West-Central Florida was also gripped in drought and has enacted some of the tightest water restrictions in recent memory. Flows on the Hillsborough and Alafia rivers, which help supply Tampa and St. Petersburg’s drinking water, are now on the rise after experiencing record low flows for this time of year. Fire danger, which had been extremely high across Central and South Florida with Keetch-Byram Drought Index values from 600 to over 700 (corresponding to extreme dryness), is now greatly diminished. Current KBDI values have dropped to 300 or less across South Florida and soils are completely saturated across North and Central Florida. The widespread rainfall has sufficiently moistened soils and greened up vegetation, and combined with onset of Florida’s summer rainy season, effectively ends the active wildfire season.