A WSR-88D data analysis of cyclic tornadic mesocyclones associated with tropical cyclones
Grams, Dan Joseph
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Only recently has the problem of forecasting tomadic activity associated with tropical cyclones been thoroughly addressed. The deployment of the WSR-88D (Weather Surveillance Radar-1988 Doppler) has allowed meteorologists to fiirther investigate the storm-scale characteristics of tomadic mesocyclones produced within a tropical cyclone environment. Radar-derived physical parameters along with algorithm-derived products have provided some very detailed information about the behavior of these storms. This thesis is an investigation of two cyclic tomadic mesocyclones associated with tropical cyclones using WSR-88D data. A tomadic mesocyclone that occurred on 2 September 1998 in association with Hurricane Earl and another on 4 November 1998 in association with Tropical Storm Mitch. Level II radar tapes recorded from the Tampa Bay (KTBW) National Weather Service Office during Hurricane Earl's approach and from the Miami (KAMX) office during Tropical Storm Mitch were processed and thoroughly analyzed. Common storm-scale characteristics for both mesocyclones during the times of tornadoes were found. A decreasing diameter of the low-altitude mesocyclone was found to occur before a tornado touchdown. Base reflectivity images displayed hook appendages and inflow regions during tornado events typically associated with tomadic storms of the Great Plains. Analysis of algorithm-derived trends displayed these fluctuating rotational diameters corresponding to the mesocyclones strength indicating that the mesocyclones were cyclic in nature. Additional data from area soundings provided a synoptic view for each event that displayed an atmosphere lacking the necessary thermodynamics needed for tomadogenesis. Very strong low-level wind fields seemed to be the only major meteorological contributor.