Over the last several Atlantic tropical cyclone (TC) seasons, a multitude of storms have affected the state of Florida. Doppler radar (WSR-88D) interrogation of the TC rainbands have revealed many significant characteristics, including a predominance of long-lived mesocyclonic cells. Typically, the reflectivity cores and depths of rotation remained relatively shallow, and appeared quite similar to "mini-supercells" which are common within (non TC) low buoyancy-high shear environments.
Radar data from five TC's in particular will be examined: Gordon (1994), Allison, Erin, and Opal (1995), and Josephine (1996). One similarity amongst all systems was the persistence of a dominant outer rainband in which numerous mesocyclones (families) formed. The majority of these rainbands formed over the Atlantic or Gulf of Mexico and later moved onshore. Two of the rainbands formed in a unique concave orientation, closely matching the adjacent coastline configuration. Not all circulation families developed within linear features however, as some cells developed in-situ and acquired rotation, but remained in close proximity to one another. Other peculiar rainband configurations mimicked a line echo wave pattern (LEWP) and a "question mark" echo.
The circulations typically existed in families of three, however as many as eight cells with persistent rotation were detected within one particular outer band. The average duration of the individual storm scale rotations were two to three hours, however the dominant rainbands often lasted six hours or more. Many of the mini-supercells were responsible for one or more tornadoes/waterspouts, including several which resulted in considerable damage (F2 on Fujita scale).
Meteorologists and the public alike often concentrate on the severe weather effects associated with the inner TC bands. However, given the likelihood of mesocyclone families capable of producing tornadoes within the outer bands, attention needs to be given to these areas as well. This poster will document the radar appearance, configuration, and geographic orientation of numerous dominant outer rainbands containing circulation families. Individual families will be displayed in detail via radar reflectivity and velocity products, and cells which produced tornadoes will be highlighted. It is hoped that this poster will help educate forecasters how to anticipate and identify potentially dangerous mini-supercells early in their development, allowing for more accurate public forecasts and warnings and therefore increased preparation times.