Structural variability of miniature supercells in tropical cyclone rainbands

Tornadoes spawned within the outer rainbands of landfalling tropical cyclones regularly pose a great threat to coastal regions. These tornadoes and their parent supercells, while less intense than there Great Plains counterparts, can still cause considerable loss of live and property damage. Much of the challenge faced by forecasters is to identify which convective cells will become tornadic out of the hundreds that often move onshore. If common distinguishing features of the tornadic cells can be identified while the cells are still offshore and nontornadic, then forecasters may be able to increase their lead time and better forewarn the public. The objective of this study is to document the structure of multiple offshore convective cells within outer TC rainbands in order to gain a better understanding of their spectrum and the common characteristics that precede tornadogenesis.

This study compares and contrasts the three-dimensional structure of convective cells embedded within the outer rainbands of Hurricanes Ivan and Jeanne of 2004 as the cells transition from well offshore to over land. An extensive dataset composed of airborne WP-3D and WSR-88D radar data, rawindsondes, GPS dropsondes, and aircraft flight-level data is employed. The three-dimensional winds and convective structure within offshore convective cells are documented via dual-Doppler analyses. Thermodynamic structure is inferred from available flight-level, GPS dropwindsonde, and surface observations. Several cells in a variety of mesoscale environments exhibited supercellular structure (i.e. rotating updraft and hook echoes) both well offshore and over land. A synopsis of our preliminary results and their comparison with previous studies will be presented at the conference