11C.5
Analysis of tropical storm-tornadoes and their environments
Lori A. Schultz, University of Alabama at Huntsville, Huntsville, AL; and D. J. Cecil and C. C. Crowe
From 2000-2005, over 700 tropical storm-spawned tornadoes have struck the United States, with over 90% of them F1 or below. These small vortices are difficult to detect on radar, making them quite difficult to predict and warn on with any repeatable skill. A climatology study looking at the validity of the past assumptions in what we know about tornadoes formed in/by a hurricane has been put together using the Hurricane Best Track Files (HURDAT) database as put out by the Hurricane Research Division (HRD). The data set was made available on the National Hurricane Center's (NHC) website which was used in conjunction with the ASCII Tornado Data (ONETOR) database as found on the Storm Prediction Center's (SPC) archived storm reports page. It is possible to limit the search by range, azimuth, month of occurrence, and number of tornadoes associated with the storm. Additionally, a map of storm track, size, and paths of tornadoes relative to the storm's track can quickly be plotted alongside statistics including number of tornadoes by f-scale, damage estimates, fatalities, and other like data. The entire 50+ year span of storms is being reviewed looking to further solidify or disprove any previous hypotheses concerning the likelihood of occurrence in specific quadrants of the storm (right front), time span after landfall (hours to days), and range from the center of the hurricane (core tornado vs. rainband tornado). The majority of hurricane spawned tornadoes occurred between 360° and 120° , relative to the storm's forward motion, which is in agreement with previous work. Another result, as can be seen in the attached figure, further confirms the majority of the storms occur within 200-400 km of the coast. From the climatological studies, particular cases will be examined to look at the conditions and mechanisms associated with tornado-genesis using available radar products and satellite imagery. These include vertical shear characteristics, especially those associated with the outer rainbands, and evidence of dry air intrusion, hypothesized to enhance the thermodynamic environment, making it more favorable to storm genesis. Additionally, study will be done on the evolution of the embedded storm structure in the outer rainbands in two regimes: (i) while the hurricane center is over water and the rainbands are making landfall, and (ii) in the decaying stages of the tropical storm, possibly a day or two after landfall. This section of the analysis generally follows the work outlined in McCaul et al., 2004 where the TC Beryl outbreak was looked at in depth. The intent of this work is to define characteristics that distinguish landfalling hurricanes and tropical storms with tornadic threats in general, and to distinguish the embedded tornadic cells in particular from other suspicious, yet non-tornadic, cells
Session 11C, Tropical Cyclones at Landfall
Wednesday, 30 April 2008, 1:15 PM-3:00 PM, Palms H
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