Synoptic Scale Analysis of Tornado Producing Tropical Cyclones

Ariel Cohen
NOAA/National Weather Service
Weather Forecast Office
Jackson, Mississippi

ABSTRACT

     Composite mean synoptic analyses are presented for seven different meteorological variables to distinguish between landfalling tropical cyclones along the coast of the Gulf of Mexico that are substantially tornadic (tropical cyclones that produce at least four tornadoes) and those that are not substantially tornadic (tropical cyclones that produce no more than one tornado). From 1985 to 2006, 15 landfalling tropical cyclones were identified as being substantially tornadic, while an additional 15 were identified as being non-substantially tornadic. These 30 tropical cyclones are considered separately amongst three sectors along the Gulf Coast in computing mean synoptic variables. Some findings for substantially tornadic tropical cyclones were: (1) the southeastern United States was broadly located within the right entrance region of an upper-level jet streak centered over the northeastern United States; (2) organized, large, and directionally-symmetric 850-hPa flow was maximized in the northeastern semicircle of the cyclonic envelope; (3) a distinct, organized, and symmetric mean sea level pressure pattern over the Gulf was associated with the tropical cyclones; (4) a strong 600-hPa relative humidity gradient was present in the northeastern semicircle of the cyclone; and (5) a dry intrusion was found in the eastern semicircle in some cases of substantially tornadic tropical cyclones. These commonalities associated with the substantially tornadic tropical cyclones were not found to be associated with the non-substantially tornadic tropical cyclones.



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