Extended Abstract (136K)16A.8
Radar derived structures of tornadic mesocyclones from Tropical Cyclone (TC) Frances (1998) in Texas and Louisiana
Gandikota V. Rao, St. Louis Univ., St. Louis, MO; and J. W. Scheck and R. Edwards
Frances was a tropical cyclone that occurred in the western Gulf of Mexico in September 1998, making landfall near Corpus Christi, Texas at 0600 UTC 11 September. Frances was not officially classified as a hurricane, but did produce several supercells and tornadoes in Texas and Louisiana during its landfall phase. One F0 tornado was recorded about 100 km south of Houston in Matagorda County. Radar structure of the associated mesocyclone was studied using the WSR-88D Level II data from Houston and WATADS software for around 2342 UTC 10 September. The mesocyclone bearing a maximum reflectivity value of 45 dBZ along with many convectively active regions was seen in a rainband stretching south southeastward along the Texas coast. Features of this mesocyclone will be discussed, including wind field asymmetry, inflow layer development, and differential friction between land and water. In addition to this mesocyclone several separate mesovortices were found by radar during the TC's landfall.
After landfall, TC Frances executed a small cyclonic loop for 12 hours and then moved across eastern Texas as a weak depression, subsequently producing ten tornadoes (F0 and F1) in Louisiana. The CAPE value at Lake Charles, LA for 0000 UTC 12 September was 1470 J/kg and the storm relative helicity was 190 meters squared per seconds squared. These values were thought to be moderately favorable for the production of mesocyclones bearing tornadoes. These mesocyclones developed only 45 dBZ maximum reflectivity and extended up to roughly 5 km above ground level, based on Fort Polk, LA radar data beginning at 1448 UTC 11 September. Though shallow, they inflicted heavy property damage (in excess of 10 million dollars) in many parishes (Jefferson Davis, F1; Acadia, F0; Evangeline, F1; Allen, F0) of southern Louisiana.
Several characteristics of the mesocyclones will be shown in tabular form, including: mean rotational velocity, mean horizontal and vertical extents, mean maximum reflectivity, mean inward and outward Doppler wind components, CAPE, helicity, and lifespan. Also, the evolution history of each mesocylcone as revealed by radar, the underlying dynamics and the potential for short-range forecasting will be presented. Finally, characteristics of mesocyclones of Frances will be compared with similar characteristics of mesocyclones deduced from earlier TC supercell studies in Florida and South Carolina. This research was performed under UCAR-COMET Outreach sponsorship.
Session 16A, Tropical Cyclone Observations and Structure V (Parallel with Sessions 16B and 16C)
Friday, 3 May 2002, 8:30 AM-10:30 AM
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