December 16th 2020 Tornadoes

Affected Pinellas, Hillsborough, and Polk Counties

Synopsis:

In the days leading up to Wednesday December 16th, the Storm Prediction Center in Norman, OK along with the Tampa Bay Area National Weather Service office began highlighting and messaging the risk of severe weather during the middle of the week. Ahead of a cold front and south of the warm front, West Central and Southwest Florida were located in the warm/moist sector of a closed surface low. Conditions were only marginally conducive for severe weather as cold shelf waters off the coast of Florida would likely limit instability. Nevertheless, enough of the ingredients including bulk shear of 40-50 knots and 0-3 km Storm Relative Helicity in excess of 200 m^2/S^2, were in place to warrant the introduction of a Marginal Risk of tornadoes and damaging wind as early as the Day 3 Convective Outlook (image below).

The greatest threat initially appeared to be over the Big Bend and Nature Coast regions. However, early pre-frontal stratiform rainfall over these areas likely overturned the atmosphere enough to dampen the severe threat as no severe storms were observed. On the southern periphery of the highlighted threat area, daytime surface heating was enough to sustain convective updrafts if they happened to make it on land. One such cell did just that. Firing up over the warm and unstable waters near the Gulf Loop Current, this particular cell had a long history of doppler indicated waterspouts before weakening over the cooler Gulf waters near Pinellas county. Once it reached land, the cell tapped into the southern end of more favorable environmental conditions, spawning a series of tornadoes that damaged homes and businesses across three counties. Fortunately, there were no reported injuries or fatalities.

Pinellas County EF-2 Tornado

The first tornado warning of the day was issued at 3:48 PM EST for Central Pinellas County. At approximately 3:49 PM EST, a tornado touched down near the Bayou Club between Pinellas Park and Largo. A National Weather Service meteorologist later surveyed the damage and found a long swath of EF-1 and EF-2 damage, primarily in the vicinity of Bryan Dairy Rd and 66^th St N. Peak winds were estimated to be 125 mph. Tower observers at St. Pete Clearwater International Airport witnessed insulation and other debris gathering around the airport’s perimeter fence.

The tornado stayed on the ground as it moved northeast across the county, eventually crossing the west end of the Howard Frankland Bridge at 4:09 PM where motorists witnessed a light pole getting knocked down. The tornado remained parallel to the bridge as it made its ominous approach towards Tampa. Near the Pinellas/Hillsborough county border, doppler radar indicated the strongest rotation yet as the waterspout continued across Old Tampa Bay. Due to the trajectory towards a very populated area, and nearing the busy rush hour commute, an enhanced tornado warning was issued containing the wording, “Particular Dangerous Situation”. Tampa International Airport was contacted about the impending threat as well. Thankfully, the tornado quickly weakened before it reached land in Hillsborough county. Only a couple sporadic, inconclusive damage reports came in around Westshore – and it was determined the tornado had already dissipated before it reached West Tampa.    

Hillsborough & Polk Counties EF-1 Tornado

After the tornado spared the Tampa area, meteorologists remained vigilant in watching this particular cell – despite the rather meager atmospheric conditions and being surrounded by stratiform precipitation. As it turns out, the storm did indeed re-strengthen and doppler radar signaled the storm might produce another tornado. A tornado warning was promptly issued at 4:42 PM EST as it approached the northeast part of Hillsborough county.  

The same storm produced its second tornado of the day north of Plant City on the south side of Knights Griffin Rd E in extreme Eastern Hillsborough county. NWS meteorologists conducted a survey where they found EF-1 damage to a mobile home, a farm building, and downed oak trees in a cattle field. The tornado crossed Knights Griffin Rd E where it moved over mostly rural area with little population and cross roads. Damage was not found in this area, and it’s likely that the tornado lifted above tree level as it traversed northeast into Polk county. The most significant damage was done later in the tornado’s life cycle when it reached the north side of Lake Gibsonia. Meteorologists determined the track in this area to have a more northerly component, likely due to the occlusion of the tornado. Widespread EF-0 damage was confined to properties across approximately 3 north-south oriented streets. Damage consisted of mostly tree & fence damage along with downed pool enclosures. One home in particular sustained significant structural damage with a loss of half its roof and a compromised exterior wall. This was rated as a high-end EF-1 with peak winds estimated at 110 mph. The tornado quickly dissipated once it crossed W Daughtery Rd and this concluded the severe weather for the day. This tornado event illustrated a collaborative effort between the National Weather Service, media partners, and emergency management which undoubtedly helped to save lives.