Hurricane Frances - Meteorological History

Meteorological History

A strong tropical wave moved off the west coast of Africa on August 21. Moving under the base of the subtropical ridge, it moved westward for several days, remaining disorganized despite favorable conditions. Thunderstorms associated with the wave finally began organizing early on August 24, and the system became a tropical depression that evening. Good upper-level outflow was observed in all but the eastern quadrants as the depression continued on its path, and the depression strengthened to tropical storm status on August 25, approximately 1,420 miles (2,290 km) east of the Lesser Antilles.

The tropical storm, now named Frances, further intensified on August 26 in an environment of low vertical wind shear as its track bent to the west-northwest. Frances rapidly intensified, developing an eye and reaching hurricane strength late that afternoon. An approaching upper level trough caused Frances to move more northwesterly on August 27. The cyclone reached its primary peak intensity of 135 miles per hour (217 km/h) on August 28. The hurricane turned back to its original westward motion on August 29, as the upper trough moved away the region and the subtropical ridge strengthened to Frances' north.

Over the next day, the hurricane underwent an eyewall replacement cycle, during which the maximum sustained winds decreased to 115 miles per hour (185 km/h). This weakening trend was short lived, and the storm reintensified during the afternoon of August 30, as vertical wind shear remained low. The storm continued strengthening as it turned west-northwestward, reaching its peak intensity of 145 miles per hour (233 km/h) on September 2 while 555 miles (893 km) east-southeast of West Palm Beach, Florida. On September 2, Frances entered the Bahamas, passing directly over San Salvador Island and very close to Cat Island. The storm weakened to a Category 3 hurricane by 2 pm, which was initially attributed to inner core processes, but increasing westerly winds aloft, and the resultant vertical wind shear, was later determined to be the cause. On September 3, Frances passed into the vicinity of Abaco Island and directly over Grand Bahama while continuing to slowly weaken. The storm regained Category 2 hurricane intensity prior to passing over Grand Bahama Island and also slowed in forward speed due to a weakness in the subtropical ridge to its north. Parts of South Florida began to be affected by squalls and the outer rainbands of the hurricane at this time. Gusts from 40 miles per hour (64 km/h) to as high as 87 miles per hour (140 km/h) were reported from Jupiter Inlet to Miami.

Frances moved slowly, between 5 miles per hour (8.0 km/h) to 10 miles per hour (16 km/h), as it crossed the warm Gulf Stream between the Bahamas and Florida, leading to the concern that it could restrengthen. However, Frances remained stable at Category 2 intensity with 105 miles per hour (169 km/h) maximum sustained winds while it battered the east coast of Florida between Fort Pierce and West Palm Beach for much of September 4. At 11 pm, the western edge of Frances' eyewall began moving onshore. Because of Frances' large eye, which was roughly 80 miles (130 km) across, and its slow forward motion, the center of circulation remained offshore for several more hours. At 1 am EDT on September 5 (0500 UTC), the center of the broad eye of Frances made landfall along the Florida coast, at the southern end of Hutchinson Island, near Sewall's Point, Jensen Beach and Port Salerno, Florida. Late on September 5, Frances picked up speed due to a strengthening high pressure system to its north and crossed the Florida Peninsula, emerging over the Gulf of Mexico near Tampa as a tropical storm. After a short trip over the Gulf of Mexico, Frances made a second landfall near St. Marks, Florida. Frances headed inland, weakening to a tropical depression and causing heavy rainfall over the southern and eastern United States. As Tropical Depression Frances turned northeast, United States meteorologists at the Hydrometeorological Prediction Center continued issuing advisories on the system until it crossed the Canadian border into Quebec, where heavy rainfall also fell.