Major and 'life-threatening flooding' continues as Sally moves inland
"Life-threatening” flooding unfolded Wednesday across portions of southern Alabama and the Florida Panhandle -- with major flooding expected to continue into late week as Sally creeps across the southeastern United States as a tropical rainstorm.
AccuWeather meteorologists are predicting torrential rainfall from Sally will deluge a large part of the southern United States in a slow-motion flooding disaster.
Ongoing torrential rain will first lead to flash flooding of urban areas, followed by quick rises on small streams and then significant rises on the area rivers.
Cities that endured heavy as Sally crawled along include Charlotte, Raleigh and Greensboro, North Carolina; Columbia and Greenville, South Carolina; Atlanta, Augusta and Macon, Georgia; and Norfolk and Richmond, Virginia. Montgomery, Alabama, was hit hard by heavy rain and gusty winds that caused urban flooding and knocked down trees.
Sally's excessive rainfall over the 24-hour period, ending around 10 a.m. EDT Wednesday, Sept. 16, 2020, can be seen above, with the heaviest amounts seen across southern Alabama and the western portion of the Florida Panhandle. (AccuWeather)
The inland flooding threat follows surge inundation and damaging winds that occurred as Sally made landfall as a Category 2 hurricane near Gulf Shores, Alabama, early Wednesday morning.
A repeat of the magnitude of Harvey's flooding in 2017 did not occur, but Sally's forward motion remained slow following a pause along the central Gulf Coast. Sally will unload excessive rainfall on portions of Alabama, Georgia, the Carolinas and southeastern Virginia as it takes a curved northeastward path through the end of the week. An increase in forward speed accompanied Sally's inland path.
Harvey deposited up to 61 inches of rain in southeastern Texas as it stalled for several days from late August to early September and claimed the lives of more than 100 people.
Hurricane Ivan, in 2004, was the last hurricane to make landfall in Alabama. The powerful storm made landfall as a major, Category 3 hurricane on the Saffir-Simpson scale, but was designated as a 4 on the AccuWeather RealImpact™ Scale for Hurricanes. Ivan is one of only three hurricanes to make landfall in Alabama during the past 31 years, following Hurricane Danny in 1997 and Hurricane Frederic in 1979.
Factoring in increasing forward movement of Sally should avoid a total "Harvey effect," but excessive rainfall is still anticipated with widespread flooding problems over the Southeastern states.
"A large swath of 4- to 8-inch rainfall is forecast from the central Gulf Coast to near the southern Appalachians and onward toward a portion of the Atlantic coast," according to AccuWeather Meteorologist Matt Benz. The AccuWeather Local StormMax™ rainfall forecast to be near 30 inches was realized in the northwestern tip of the Florida Panhandle in the Bellview area.
The heaviest rain tapered off over the western part of the Florida Panhandle and the Alabama Panhandle late Wednesday.
The excessive rainfall amounts from Sally are extremely rare. Rainfall topping 2 feet in 24 hours near the Alabama Panhandle and the western tip of the Florida Panhandle, tends to occur once every 200 years, on average, according to Atlas 14, a publication by the National Weather Service. This guide is used by insurance companies, hydrologists, civil engineers and other interests to determine how often various rainfall events occur. A 30-inch rainfall in 24 hours in the area is considered to occur once every 500 years on average, based on the publication.
Even though there were small pockets of abnormally dry soil conditions in the region prior to Sally's arrival, rainfall of this magnitude will lead to widespread incidents of flash flooding and urban and small stream flooding. Significant rises on the rivers in the region are likely as well with the potential for moderate to major flooding in unprotected locations.
Sally's excessive rainfall over the 24-hour period, ending around 6 a.m. EDT Thursday, Sept. 17, 2020, can be seen above. The swath of additional heavy rain is pointing northeastward toward central North Carolina and southeastern Virginia. (AccuWeather)
Flooding along small streams and in poor drainage areas may be almost immediate, but it may take a few days for the larger rivers to respond to the rainfall.
Some of the rivers at significant risk for big rises and flooding following the heavy rain this week include the Coosa, Alabama, Escambia, Chattahoochee, Mobile, Apalachicola, Flint, Savannah, Rocky and Pee Dee.
Property owners and officials in flood-prone areas should closely monitor this situation. Motorists should anticipate having to take alternative routes to work or school as the big rain hits and streams rise into late week. Due to excess water on the roads and poor visibility during the torrential downpours, motorists should slow down to reduce the risk of hydroplaning.
National Weather Service hydrological river gauge forecast information were not initially reflecting all of the upcoming rainfall away from the Gulf Coast region. Stage forecasts along the rivers north of the I-10 corridor to the I-85 corridor may continue to trend significantly higher into the end of the week as information is fed into computers.
The Shoal River near Mossy Head, Florida, reached record stage above at 25.65 feet Wednesday night, breaking the old record of 24.7 feet.
Excessive rainfall could harm cotton and peanut crops in parts of the southern U.S. Low-lying fields could be left submerged for a week, which could run the risk of peanuts rotting in fields. Harvest is just beginning now, so this could put a damper on yield. The Florida Panhandle and southern Alabama produce about 20% of U.S. peanuts. Some wind and rain damage could occur to cotton crops, particularly in southern Alabama.
Even though the intense portion of the rainfall is forecast to thin out farther to the northeast, the ground is generally more wet in portions of the Carolinas and southern Virginia, so it cannot hold as much moisture. There can still be isolated flash and small stream flooding in these areas as a result late this week at moisture from Sally joins up with a non-tropical storm system.
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