2012 Tropical Storm Debby tornado outbreak

From June 23 to 26, 2012, Tropical Storm Debby produced a significant tornado outbreak across the Florida Peninsula. Throughout the entire event, 25 tornadoes touched down across the state, making the outbreak the second largest on record in Florida, behind only that spawned by Hurricane Agnes, which produced 28 tornadoes from June 18 to 19, 1972. At least ten of the tornadoes—the largest 24-hour total in South Florida since Hurricane Isbell produced eight in 1964—had been confirmed in four South Florida counties by the National Weather Service forecast office in Miami.

Meteorological synopsis
On June 19, 2012, an area of low pressure formed over the Yucatán Peninsula and slowly moved north-northeast. Concurrently, a tropical wave approached from the east and merged with the low on June 22 which led to the formation of a trough across the southern Gulf of Mexico. Over the next day the system became increasingly organized and developed into Tropical Storm Debby around 8:00 a.m. EDT (UTC−04:00) on June 23. A prominent convergence band developed east of the circulation center and posed a minimal risk of tornadic activity over the Florida Keys and southwestern Florida Peninsula. Ample low-level moisture and air temperatures above 80 F created Convective Available Potential Energy (CAPE) of 2,000 J/kg. The first tornadoes occurred more than 40 hours before landfall and were in the city limits of Naples within Collier County at 3:35 p.m. and 4:00 p.m. EDT; both were rated EF0. This was atypical to the majority of tropical cyclone tornado events in which the bulk of activity occurs within hours of landfall and after. By 4:44 EDT, weak thunderstorm cells were noted over Collier and Monroe Counties; however, they were not considered as significant as normal tropical cyclone-produced supercells. Activity in the nighttime hours shifted to potential waterspouts moving onshore in southwestern counties. Conditions became more conducive for tornadic activity by the late-morning hours of June 24 as Debby's broad circulation meandered generally northeast. Storm-relative helicity reached 250–300 m2/s2, indicating potential for tornadoes. Accordingly, the Storm Prediction Center (SPC) issued a tornado watch for western Florida at 11:45 a.m. EDT.

By the afternoon of June 24, the focal point of discrete and/or rotating cells extended from the Tampa Bay area southeast to the Miami metropolitan area along a baroclinic zone. However, the eastern cells were inhibited by a more stable airmass. Along the western side, instability was enhanced by the entrainment of dry mid-level air into areas with MLCAPE of 1,000 J/kg. Bulk shear also exceeded 35 mph, values supportive of tornadic storms. Analysis of surface winds by the SPC at 7:01 p.m. EDT showed a 60 mph low-level jet and increasing helicity values of 300–500 m2/s2. Successive mini supercells moving from the Gulf into western Florida were possible. By 9:16 p.m. EDT, the convergence band organized into a linear squall line and propagated east, emerging over the far western Atlantic Ocean near 12:00 a.m. EDT on June 25. Behind the squall, the overall environment became more stable and less conducive to tornadic activity. Around this time, Debby's center stalled out south of the Florida Panhandle. In the pre-dawn hours of June 25, a new band of thunderstorms developed over central Florida and a new tornado watch was issued at 4:40 a.m. EDT. Poorly modeled dry air entrainment and subsidence ultimately suppressed formation of tornadic storms throughout the day. Only one tornado touched down in Highlands County at 10:25 a.m. EDT on June 26, marking the end of the outbreak.

Throughout the nearly three-day outbreak, 25 tornadoes were confirmed across Florida of which only one exceeded EF1 intensity. As is the case for all tropical cyclone tornado events, an unknown number of tornadoes likely went undocumented over open waters. The most active phase of the outbreak occurred from 10:00 a.m. on June 24 to 12:00 a.m. EDT on June 25 with 22 tornadoes. Nineteen tornadoes formed within the right-front quadrant of Tropical Storm Debby&mdash;relative to the storm's motion&mdash;while the remainder formed in the right-back quadrant.