An upper-level trough located east of the Bahamas began to produce shower and thunderstorm activity around September 9. It tracked slowly westward over the next day and brought heavy rain to the northern Bahamas. On the 10th, it began to organize very quickly: convection increased and allowed the circulation at the upper-levels to work down to the surface. Sea level pressures were falling by September 11 and the spin tightening. That afternoon, Tropical Depression Nineteen was designated between Andros Island and the south Florida coastline.
Overnight, the depression moved over the southern Florida peninsula. Most rain, apart from some outer bands, was occurring south of the center. Convection continued to increase in this area, but the low-level swirl evident on visible imagery lifted more northward on September 12 and paralleled the western Florida coastline. Surface observations near the tip of the Florida peninsula justified an upgrade to Tropical Storm Sally that afternoon. Sally broke the record for earliest 18th named storm, or "S" storm, crushing the mark set by 2005's Stan, which was named on October 2 of that year.
By September 13, Sally had moved further over the Gulf of Mexico, and was strengthening steadily. The center was still moving west-northwest out a bit ahead of the associated thunderstorms, but overall organization was increasing as outflow and banding became more pronounced. Soaking rains lingered over southwestern Florida through that afternoon until Sally moved farther away. Beginning that evening, a central dense overcast (CDO) exploded over the system and expanded in all directions. The morning of September 14 arrived with a much larger Sally in the Gulf of Mexico, though the centers were still not vertically aligned.
However, Sally's structure underwent another large change later that morning: the old low-level center dissipated and a new one formed farther northeast near the center of the CDO. This sparked a burst of intensification that brought the storm from a strong tropical storm to a category 2 hurricane with peak sustained winds of 100 mph. The surge in wind speeds only halted that evening when some dry air entered the circulation from the southwest. Sally was moving very slowly west-northwestward, only about 100 miles from the Gulf coastline, so that prolonged heavy rains affected the Florida panhandle and soon pushed into coastal Alabama and Mississippi.
By that time, steering currents had largely collapsed and Sally's motion was little more than a drift. The next day, the hurricane turned more to the north, though there were many short-term wobbles, and the forward speed was only about 2 mph. Aircraft measurements indicated that Sally's winds had dropped back to category 1 strength, perhaps due to upwelling of cooler waters or upper-level winds. However, the system's satellite presentation remained very organized and the central pressure actually dropped the afternoon of the 15th to new lows. At first, winds did not carch up, but as the center closed in on the coast, Sally put on one last burst of strengthening. The eye cleared out more than it had at any time previously and the storm regained category 2 strength. Sally was at its peak intensity of 105 mph winds and a minimum pressure of 965 mb when it made landfall just west of the Alabama/Florida border a bit before 5:00 am local time on September 16.
The system turned northeast over land, still hardly gaining speed, and rapidly weakened throughout the day. It became a tropical storm that afternoon and a depression that evening. Torrential rain spread through Georgia and the Carolinas even after Sally was downgraded to a remnant low on September 17. Rain totals along the Gulf coast of Florida and Alabama exceeded 15 inches over a wide region, with over 20 inches in several places. The remnants of Sally finally moved into the Atlantic on the 18th and soon merged with another system.
The above infrared satellite imagery shows Sally intensifying a few hours before landfall.
Sally moved very slowly before landfall and caused widespread flooding in the Florida panhandle and the Alabama coast.
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