Wednesday, 13 January 2016
The frequency of non-supercell waterspouts in the vicinity of the Florida Keys is higher than any other location in the United States and is arguably the highest in the world. Local Storm Reports and the National Centers for Environmental Information Storm Data and Unusual Weather Phenomenon database for the locally defined wet season of June through September 2006-2014 were used in this investigation. Years prior to 2006 were not considered for this study due to the rawinsonde observation location change on the island of Key West in 2005, and inconsistent reporting and waterspout identification practices. Parameters were derived from the Key West 1200 UTC soundings with approximately 20% associated with at least one waterspout report. Because of the uniform tropical marine environment over the Florida Keys in the summer, the soundings were considered temporally and spatially proximal with waterspouts reported near the island chain. Kinematic and thermodynamic parameters, as well as stability and convective indices, were obtained from these soundings. The parameters from waterspouts days were compared to days in which no waterspouts were reported, with the goal of identifying metrics for days more conducive to waterspout development. It was not possible to investigate the more general concept of comparing days when waterspouts did not occur (versus not reported), because waterspouts often go unreported and are not identifiable via proxy (i.e., radar or satellite). Previous research has found waterspouts are under reported in the Florida Keys, likely by an order of magnitude. Each parameter comparison was examined for statistical significance and consistency. Sounding parameters that showed not only statistical significance, but also utility in the forecast process, were given consideration in the development of a waterspout forecast methodology. Preliminary results found waterspout days exhibited lower layer averaged wind speed and shear through the boundary layer, and higher convective available potential energy values in the lowest few kilometers. Low shear, light winds, and increased buoyancy at the cloud scale aid the development of cumulus cloud lines, and protect convective updrafts from disruption, which are necessary processes in waterspout development.
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