On the afternoon of May 27, 1997 a large complex of strong thunderstorms moved southeast across southern Georgia and northern Florida. The thunderstorms developed in advance of a cold front which was sagging southward through Southeast Georgia. As the complex moved into extreme Southeast Georgia and Northeast Florida, it interacted with the east and west coast sea breezes and a very unstable atmosphere, causing severe thunderstorms to develop. Numerous severe thunderstorm warnings were issued for counties in Southeast Georgia and Northeast Florida. There was widespread hail of one inch size and larger (Fig. 1 ), extensive wind damage reported, and two tornado warnings were issued (Local Storm Reports).
This report is put together to show you a brief sequence of events as they unfold during the day of the 27th, particularly the severe thunderstorm that hit metropolitan Jacksonville. Severe thunderstorms originated first in Jeff Davis County in Southeast Georgia near 1230 pm in the afternoon. As the storms moved southeast they reached extreme Northeast Florida by 400 pm and then moved southeast along the coast through the evening hours. A total of 31 warnings were issued by the National Weather Service in Jacksonville.
One particular severe thunderstorm moved across the Jacksonville metropolitan area between 515pm and 600pm (Fig. 2). The thunderstorm produced 1 inch hail and damaging winds in excess of 100 mph across the central and western part of the city. The wind damage resulted from a large asymmetric microburst or downburst which initially hit the downtown area around 525 pm (Fig. 3, note the 69 dbz pink colored core at X4. This indicates the core or the center of the falling hail). The downburst spread southward causing extensive damage across the Riverside, San Marco, Ortega and NAS Jacksonville areas between 530pm and 600pm. Fig. 4 shows the wind field across Duval County as depicted by the Doppler Radar at 538 pm. Note the wind maximum over the St Johns River near Ortega. This denotes wind in excess of 80 knots (92 mph) at 500 feet above the ground. Fig. 5 shows the same wind field at 544 pm moving over NAS JAX (NIP). The figure shows a maximum wind of 78 knots (90 mph) at 500 feet above the ground. The last two figures depict the downburst path moving southward from near the downtown area and across Riverside and NAS JAX.
These two figures indicate that the majority of the damage was caused by the downburst. Although it is possible a small short lived tornado was generated on the flank of the downburst, the vast majority of the damage was caused by straight line winds associated with the downburst. The probable cause of the downburst itself was hail of large size falling through the atmosphere from 50,000 feet. Fig. 6 shows the thunderstorm tops as depicted by the Valdosta Doppler Radar (Moody Air Force Base). Notice they exceed 50,000 feet (nearly 10 miles up in the atmosphere) over Duval, Marion and Suwannee County.
Here is a list of products issued by the National Weather Service in Jacksonville from early in the morning of the 27th. In the sequence of these products you will see that the thunderstorms evolution, including the point of origin, time evolution, and strength were well forecast and warned.