A series of weak surface low pressure systems draped across the the deep south including the central Florida peninsula combined with an approaching cold front over a very saturated airmass triggered a cluster of storms over Nassau county that produced a strong outflow that tracked SE over western Duval county. When this outflowed encountered ESE flow and feeder bands moving inland from the Atlantic, the cell became nearly stationary over southern Duval and NE Clay counties where it produced flash flooding during the evening. The cell pulsed up and became severe over northern St. Johns county where low level helicity was greatly increased from the strong 20 kt surface winds from the ESE on the north side of a meso low that lifted northward over Alachua and Putnam counties. The cell began to strong very strong and deep layer rotation over northern St. Johns county, and a tornado warning was issued. The cell then collapsed within the next few radar scans, but weak rotation was still present. When a very strong downburst raced southward over St. Johns county, the downburst produced widespread damage to farmland near Elkton and a weak EF1 tornado touched down, on the bookend of the downburst. Flooding rainfall and deep hail drifts of penny size hail caused extensive damage to cropland near Elkton, with severe financial impact to farmers in the area.

Flood in DUVAL, FLORIDA
From 04-MAY-13 11:00:00 to 04-MAY-13 11:00:00 (EST-5)
Location: GOODBYS
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Minor flooding was reported at Happy Bluff and Forest Circle. Water was backing up through storm drains due to elevated water levels in the St. Johns River. The cost of flooding damage was estimated.

Flood in DUVAL, FLORIDA
From 04-MAY-13 18:55:00 to 04-MAY-13 18:55:00 (EST-5)
Location: JACKSONVILLE
Flood cause: Heavy Rain
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Public

Flooding occurred in San Marco between San Marco Blvd and LaSalle Street. The cost of damage was estimated.

Coastal Flood in DUVAL, FLORIDA
From 04-MAY-13 15:40:00 to 04-MAY-13 15:48:00 (EST-5)
Reported by: NWS Employee

Water was overflowing the docks at the Fort George Island Docks. The NOS Tidal Station at Mayport measured an elevated water level of 6.58 ft MLLW which was 1.75 ft above predicted levels. Minor flooding typically begins at 6.4 ft MLLW.

Hail in ST. JOHNS, FLORIDA
From 04-MAY-13 19:39:00 to 04-MAY-13 19:39:00 (EST-5)
Location: BAKERSVILLE
Magnitude: 0.75 
Reported by: Public

Hail was reported at State Road 16 and International Golf Parkway.

Flood in ST. JOHNS, FLORIDA
From 04-MAY-13 20:15:00 to 04-MAY-13 22:15:00 (EST-5)
Location: PALM VLY
Flood cause: Heavy Rain
Property damage: 0.00M
Crop damage: 38.25M
Reported by: Public

Street flooding occurred along State Road 16 and State Road 13. Widespread water over the roadways was reported. The public reported flooding at Lake Julia in the vicinity of Sawgrass County Club in Pone Vedra. Heavy rainfall combined with drifts of hail caused major crop damage near Hastings and Elkton. Potato plants were severely damaged, and about 60% of the St. Johns County potato crop was likely lost. The cost of potato crop damage to about 8,500 acres of plants was estimated to be around $38,250,000, based on a yield of $4.5K/acre of potatoes. Melons and field corn crops were also damaged. The County Commission voted to pursue federal disaster relief funding. The crops were maintained through late season freezes in February and March, so many farmers were trying to rebound from these expensive events. The damage from the heavy rainfall and hail was very devastating to farmers and suppliers.

Hail in ST. JOHNS, FLORIDA
From 04-MAY-13 20:50:00 to 04-MAY-13 20:50:00 (EST-5)
Location: MARINELAND
Magnitude: 0.75 
Reported by: Trained Spotter

Hail was observed at U.S. Highway 1 at the Flagler/St. Johns county line.

Tornado in ST. JOHNS, FLORIDA
From 04-MAY-13 20:14:00 to 04-MAY-13 20:16:00 (EST-5)
Location: ELKTON
Tornado F-scale: EF0
Property damage: 500.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A barn was severely damaged at Jen-Sar Farms and Produce store. A large barn was destroyed with noticeable debris lofted into nearby structures. A large tree was snapped at its base and fell on a mobile home causing significant damage by splitting the unit in two. Multiple trees were uprooted and fell on a boat near Elkton. The cost of damage was estimated, and is likely underestimated.

Thunderstorm Wind in ST. JOHNS, FLORIDA
From 04-MAY-13 19:25:00 to 04-MAY-13 19:25:00 (EST-5)
Location: ELWOOD
Magnitude: 50.00 EG
Reported by: Public

Trees and power lines were blown down at State Road 16 and State Road 16A. The time of damage was based on radar imagery.

Thunderstorm Wind in ST. JOHNS, FLORIDA
From 04-MAY-13 19:50:00 to 04-MAY-13 19:50:00 (EST-5)
Location: GLIMPSE OF GLORY
Magnitude: 50.00 EG
Reported by: Emergency Manager

Trees and power lines were blown down along State Road 16.

Thunderstorm Wind in ST. JOHNS, FLORIDA
From 04-MAY-13 20:20:00 to 04-MAY-13 20:20:00 (EST-5)
Location: ELKTON
Magnitude: 50.00 EG
Reported by: Emergency Manager

Trees and power lines were blown down along State Route 207. The time is estimated from radar imagery.

Thunderstorm Wind in ST. JOHNS, FLORIDA
From 04-MAY-13 20:40:00 to 04-MAY-13 20:40:00 (EST-5)
Location: ELKTON
Magnitude: 50.00 EG
Reported by: Law Enforcement

Over 60 reports of power lines damaged from fallen trees and strong winds were reported over the southwest portion of St. Johns county. The time of damage was based on radar.

Flash Flood in DUVAL, FLORIDA
From 04-MAY-13 19:00:00 to 04-MAY-13 19:47:00 (EST-5)
Location: WESCONNETT
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Public

Multiple reports of water occurred over the roads 2-3 feet deep in some areas with some structural flooding. A lot of flooding occurred between Bambi Lane and 105th Street and Interstate 295 and Blanding Blvd. The public also reported vehicles were stranded between Overland Park Blvd and Bear Creek Road. Clay County Emergency Management reported significant street flooding with impassable roads and stranded vehicles between Kingsley Avenue and Wells Road and Blanding Blvd and US-17. The Sheriff's Office reported that the Julington Creek Bridge was closed due to high water on both ends of the bridge. The bridge was later opened. The cost of damage was estimated and is likely grossly underestimated. A storm spotter measured 4.32 inches of rainfall between 6 pm and 8 pm in the Jacksonville westside. Street flooding was reported at Harlow Blvd and Cinderella Road, Harlow Blvd between Boy Blue Road and Bambi Lane, and Boy Blue Road was completely under water from Harlow Blvd to Anvers Blvd.