Saint Simons Island, Georgia Tornado May 11, 2008
Matt Zibura, Meteorologist
NWS Jacksonville, FL



Introduction
A severe weather event occurred on Sunday, May 11, 2008 across Southeast Georgia with many reports of damaging winds...large hail...and one tornado.  Doppler weather radar indicated a fast moving storm with supercell characteristics(Figure 1.) that produced the tornado.  A National Weather Service storm survey confirmed EF1 tornado damage along a 2 mile long patch in and near the Sea Palms resort area on Saint Simons Island. Path width was 1/10 to 1/8 of a mile. Many trees were snapped or uprooted along the path which caused damage to some buildings. Winds were estimated to be at 80 to 100 mph.

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Figure 1. KJAX 88D 0.5 degree Reflectivity Image, 1840Z May 11, 2008.

Synopsis
A strong low pressure system centered over the Ohio Valley pushed a cold front into the Southeast U.S. on  Sunday, May 11, 2008.  The morning sounding at Jacksonville showed a very unstable airmass along with deep layer shear and high 0-3 km helicity values(315 m^2/s^2).  Low level moisture was adequate while the mid levels were quite dry with steep lapse rates(Fig. 2).  This sounding profile combined with strong synoptic scale lift set the stage for a good chance of damaging winds, hail, and tornadoes. The Storm Prediction Center issued a moderate risk of severe weather for south Georgia and a slight risk for north Florida.  During the day numerous supercell/bow structures were detected by doppler weather radar over southeast Georgia and many severe thunderstorm and tornado warnings were issued.  The supercell that produced a tornado on St. Simons Island was the only confirmed tornado report in the NWS Jacksonville County Warning Area. A closer look at this storms environment showed a southeast wind at SSI(1429 LST) despite a strong southwest synoptic flow.  This was likely caused by an outflow boundary from previous convection. This surface wind direction increased the local low level helicity and helped provide the environment for tornado formation.  


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Figure 2. Jacksonville, Fl. Skew T, 12Z May 11, 2008

Reports
Ground truth reports from storm spotters and EMAs verified the severe weather threat.  Local Storm reports from across southeast Georgia indicated several hail reports(up to 1.5" in diameter) and damaging wind reports that downed trees.  One supercell that tracked ESE from Wayne county spawned a tornado on St. Simons Island(figure 3) just north of SSI airport.  This storm downed trees that caused structural damage to houses around 250 pm LST.  Further south over north Florida the severe threat did not materialize.  A cold front pushed through northeast Florida during the nighttime hours uneventfully.  A stronger cap and loss of daytime heating contributed to the lack of  convection over northeast Florida.


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Figure 3. Image of EF-1 tornado in St. Simon's Island. Photo was taken at SSI airport, looking toward N or NW.
Photo courtesy of Larry Wade.


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