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The 12 July 1995 Pinellas County, Florida, Tornado/Waterspout

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  • 1 NOAA/National Weather Service, Corpus Christi, Texas
  • | 2 NOAA/National Weather Service, Tampa Bay, Florida
  • | 3 NOAA/Forecast Systems Laboratory, Boulder, Colorado
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Abstract

On 12 July 1995, a tornado developed over south St. Petersburg, Florida, producing F1 damage and injuring one person before moving offshore. The tornado/waterspout was within 25 km of the Ruskin Florida WSR-88D, which provided detailed radar data. The preconvective environment was characterized by large CAPE and weak to moderate vertical wind shear, due in part to a weak upper-level cold core trough. The tornado parent cell developed rapidly in response to surface mesoscale boundary interactions. This cell was relatively short lived and nonsteady and, thus, classified as multicellular. Available data suggest that tornadogenesis occurred due to vertical stretching of preexisting vertical vorticity associated with one of the foregoing boundaries. Evidence suggests that the stretching was due to both storm updraft and convergence associated with storm downdraft. The parent cell contained a midlevel mesocyclone and mesoanticyclone pair, consistent with the proximity hodograph. This vortex pair and the tornadic circulation were separate and it is unclear what role the vortex pair contributed to tornadogenesis. This case is important since it demonstrates that a nonsupercell tornado can be anticipated before a single-Doppler radar tornado vortex signature (TVS) appears, using current nonsupercell tornadogenesis theories. Such anticipation is essential to operational forecasters in the National Weather Service, especially for cases when tornadoes are either undetectable by radar or when a radar-detected TVS does not provide sufficient lead time.

Corresponding author address: Waylon G. Collins, NOAA/NWS, 300 Pinson Drive, International Airport, Corpus Christi, TX 78406-1803.

Email: Waylon.Collins@noaa.gov

Abstract

On 12 July 1995, a tornado developed over south St. Petersburg, Florida, producing F1 damage and injuring one person before moving offshore. The tornado/waterspout was within 25 km of the Ruskin Florida WSR-88D, which provided detailed radar data. The preconvective environment was characterized by large CAPE and weak to moderate vertical wind shear, due in part to a weak upper-level cold core trough. The tornado parent cell developed rapidly in response to surface mesoscale boundary interactions. This cell was relatively short lived and nonsteady and, thus, classified as multicellular. Available data suggest that tornadogenesis occurred due to vertical stretching of preexisting vertical vorticity associated with one of the foregoing boundaries. Evidence suggests that the stretching was due to both storm updraft and convergence associated with storm downdraft. The parent cell contained a midlevel mesocyclone and mesoanticyclone pair, consistent with the proximity hodograph. This vortex pair and the tornadic circulation were separate and it is unclear what role the vortex pair contributed to tornadogenesis. This case is important since it demonstrates that a nonsupercell tornado can be anticipated before a single-Doppler radar tornado vortex signature (TVS) appears, using current nonsupercell tornadogenesis theories. Such anticipation is essential to operational forecasters in the National Weather Service, especially for cases when tornadoes are either undetectable by radar or when a radar-detected TVS does not provide sufficient lead time.

Corresponding author address: Waylon G. Collins, NOAA/NWS, 300 Pinson Drive, International Airport, Corpus Christi, TX 78406-1803.

Email: Waylon.Collins@noaa.gov

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