Monday 26 October, 2020

Hurricane Sally: Catastrophic flooding expected on the Gulf Coast

Hurricane Sally’s northern eyewall is moving across the Gulf Coast from Pensacola Beach Florida westward to Dauphin Island Alabama.

The National Hurricane Centre warns that catastrophic and life-threatening flooding is likely along portions of the northern Gulf Coast.

 A Storm Surge Warning is in effect for:

Fort Morgan Alabama to the Walton/Bay County Line Florida

 A Hurricane Warning is in effect for:

Mississippi/Alabama border to the Okaloosa/Walton County line Florida

A Tropical Storm Warning is in effect for:

East of the Okaloosa/Walton County line Florida to Indian Pass Florida

Mississippi/Alabama State Line to the Mouth of the Pearl River

Hurricane conditions are spreading onshore within the hurricane warning area in Florida and Alabama. 

Tropical storm conditions will continue in portions of the warning areas through tonight.

A few tornadoes may occur today and tonight across portions of the Florida Panhandle, southern Alabama, and southwestern Georgia.

At 4am CDT, the centre of Hurricane Sally was located about 50 miles (75 km) south-southeast of Mobile, Alabama and about 40 miles (65 km) southwest of Pensacola, Florida.

Sally is moving toward the north-northeast near 3 mph (6 km/h).

A north-northeastward to northeastward motion at a slightly faster forward speed is expected later today and tonight, followed by a faster northeastward motion on Thursday.  

On the forecast track, the centre of Sally will approach the northern Gulf Coast this morning, and make landfall in the hurricane warning area later today. Sally is then expected to move inland across southeastern Alabama tonight.

Recent data from An Air Force Reserve reconnaissance aircraft and the Mobile Alabama Doppler weather radar indicate that maximum sustained winds are near 105 mph (165 km/h) with higher gusts - a category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale.

Hurricane-force winds extend outward up to 40 miles (65 km) from the centre and tropical-storm-force winds extend outward up to 125 miles (205 km).

A sustained wind of 98 mph (157 km/h) and a gust to 116 mph (187 km/h) were recently measured by an elevated NOS CO-OP observing station in Fort Morgan, Alabama.

A University of Florida weather tower located at Gulf Shores, Alabama, reported a sustained wind speed of 75 mph (121 km/h) and a gust to 93 mph (150 km/h).

NOAA buoy 42012, located about 50 miles southeast of Mobile, Alabama, recently reported a sustained wind of 71 mph (115 km/h) and a pressure of 970.9 MB inside the eastern portion of Sally's eye.

Some slight increase in strength is possible before the centre of Sally's eye makes landfall later this morning. Rapid weakening is expected after landfall occurs.

The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline.

  

The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide.

- Dauphin Island AL to Okaloosa/Walton County Line, 4-7 feet

- Pensacola Bay and Choctawhatchee Bay, 4-7 feet

-Mobile Bay, 2-4 feet

- Okaloosa/Walton County Line to Walton/Bay County line, 2-4 feet

- MS/AL Border to Dauphin Island, 2-4 feet

- Walton/Bay County line to Chassahowitzka including Saint Andrew Bay, 1-3 feet

Through this afternoon, Sally will produce additional rainfall totals of 8 to 12 inches with localized higher amounts possible along and just inland of the central Gulf Coast from west of Tallahassee, Florida to Mobile Bay, Alabama.

Storm totals of 10 to 20 inches to isolated amounts of 35 inches is expected.

Historic and catastrophic flooding is unfolding.  

In addition, this rainfall will lead to widespread moderate to major river flooding.

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