A slow-moving soaking rain storm developing in the Gulf of Mexico will batter Florida and parts of the Deep South this weekend as millions of Americans begin their holiday travels. The intensifying storm is expected to bring gusty winds up to 50 mph and rainfall totals as high as 8” in the hardest-hit areas.
The storm will be fed by a robust jet stream supplying a deep pool of relatively cold air toward the warm Gulf of Mexico. The Gulf’s surface temperatures, while warm, are too cool for the development of a tropical cyclone. Like Nor’Easters common along the Northeast Coast in winter, bands of heavy precipitation will develop ahead of a cold front and compose a shield of precipitation north of a warm front as a conveyor belt of warm air ascends above cooler air to the north of the low. Unlike most Nor’Easters however, this storm will be slow-moving and have access to deep tropical moisture. The result will be days of heavy, wind-swept, torrential rain. Flooding and travel delays are inevitable.
The rain will commence Saturday morning as scattered showers gradually organize and intensify throughout the day in southern Louisiana, Mississippi, Alabama, and the Florida panhandle. Winds will be on the rise as cloud ceilings begin to fall during the afternoon. The dreary weather will make for poor driving conditions and could result in flight delays from cities like Pensacola, Mobile, and New Orleans.
Travelers bound for Florida’s beaches and amusements will find most of their weekend completely soiled by the slow-moving storm. Saturday night the developing low pressure system will have attained a closed circulation as it crawls northward toward the Florida Panhandle. Conditions will begin deteriorating across central and northern Florida, with blinding, wind-wrapped downpours developing over some of Florida’s biggest metropolitan areas including Tampa Bay, Orlando, Jacksonville, and Tallahassee. Downpours will be less frequent in South Florida, but Miami-Beach goers will still find their sun-bathing interrupted by high surf, gusty winds, and intermittent showers. Flight delays will be inevitable throughout the day across most of the state Sunday as a result of the low visibility and high winds from the slowly moving storm. Peak impacts in Florida from wind and frequent blinding downpours will persist through Sunday evening.
The storm’s deluge will build across southern Georgia and South Carolina Sunday afternoon and evening as it declines on the Florida peninsula. The I-95 corridor from Brunswick, GA to Charleston, SC will take the brunt of the winds and rain Sunday evening through Monday morning as the low treks toward the Atlantic Ocean. Winds here will be on the rise as the storm accelerates its intensification off-shore Monday. Its slow eastward departure will keep lingering showers around coastal areas as far north as Wilmington, NC until Monday evening.
Even where rain does not fall Monday, coastal impacts will spread as far north as the Outer Banks of North Carolina as the low churns the tides and delivers strong winds. Further south, rain may end on Florida’s east coast Monday morning, but winds will gust as high as 50 mph along the immediate coast as far south as St. Augustine in the afternoon.
Over a month’s worth of rain will have fallen by the time the rain stops in the Southeast. Widespread rainfall totals of 2-3” are expected as far north as the I-20 corridor, including cities like Birmingham and Atlanta. Rainfall totals will incrementally rise further south and east, with rainfall totals of 3-5” common in far southern South Carolina, southern Georgia, southern Alabama, and northern and central Florida. Closer to the I-10 and I-95 corridors, rainfall is expected to be even more dramatic, where locally up to 8” of rain could fall.
Excessive rainfall amounts of 8” alone would be enough to result in a substantial flood risk. But the flood risk is particularly elevated because parts of the Southeast have already recently been inundated with heavy rain. Parts of central Georgia and central South Carolina have observed over 6” of rain in just the last seven days.While the 8” bulls-eye is not expected to impact these areas, an additional 3-4” of rain in quick succession as expected is nonetheless likely to agitate ongoing river flooding and quickly result in new flooding. Below is a time-lapse from the WeatherOptics Imapct Portal of the expected WeatherOptics Flood Index across the Southeast between Saturday and Monday.
The rating corresponds to 0-10 scale, where 0 means there is no flood risk and 10 indicates catastrophic, multi-day flooding, in which submerged communities are likely cut-off from the outside world. Minor flooding of streams and rivers are possible at a Flood Index of 4. Major river flooding and urban flooding on a large enough scale such that make normal day-to-day travel becomes difficult and dangerous is described by a Flood Index rating of 7. The Flood Index for this event peaks around 7 in Southern Georgia.