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Florida State University: "Forecasting winter season coastal cyclogenesis in the Gulf of Mexico"

Final Report

A challenge to operational weather forecasters along the United States Gulf Coast during the winter season is the development of extratropical cyclones in the northwestern Gulf of Mexico. Previous studies have shown that the occurrence and rate of development of these cyclones are highly variable, making them extremely difficult to forecast with a high degree of accuracy. This project was initiated between Florida State University and the National Weather Service office in Slidell, Louisiana to address the forecast problems associated with wintertime Gulf Coastal cyclones and to develop techniques for accurately forecasting their development and movement.

In order to develop forecasting techniques for Gulf Coast cyclogenesis, an existing 39-year climatology was extended to include data previously missing. Frequencies and average pressures of winter Gulf cyclones were reviewed from 1952-1991 for each winter season (November through March). The approximate 11-year maximum Gulf cyclone frequency cycle observed by Saucier (1949) appears to continue into the winter season 82-83. A 4-year Gulf cyclone frequency cycle is also evident, embedded in the 11-year cycle beginning in the winter season 74-75 and extending through 86-87. This 4-year cycle was found to extend all the way through 90-91 for the winter season defined as December through February. A downward trend in Gulf cyclogenesis frequencies through 84-85 was also found, verifying the downward trend in North American cyclogenesis found by other researchers. Most importantly, however, an upward trend in Gulf cyclogenesis was observed from 84-85 through 90-91. An increase in average Gulf cyclone intensity with a decrease in the average number of Gulf cyclones was found during this most recent period. Also, with the newly noted upward trend in frequency, a decrease in average intensity of Gulf cyclones was found.

Correlations between cyclone frequencies and winter-season precipitation were studied to determine if the frequencies could be used as a state-wide winter-season precipitation predictor. A correlation between low Gulf cyclone frequency and below normal winter-season precipitation for all regions was found; however no good correlations were found between high frequencies and above normal precipitation. It appears that certain regions in Florida had better correlations between cyclone frequency and precipitation.