Tropical Storm Sally sloshing toward Cat. 1 or 2 hurricane Louisiana landfall|WeatherTiger
Tropical Storm Sally refuses to slow its Mustang down as it rides across the Gulf of Mexico, charting a slightly faster course that shifts the likely burden of the worst wind and surge impacts west into eastern Louisiana and southern Mississippi. The threat of flooding rainfall continues into midweek from eastern Louisiana to the western Florida Panhandle.
As of the 5 p.m. Sunday advisory from the NHC, Sally’s maximum sustained winds are around 60 mph, up 20 mph in the last day. Due to some westerly shear, most the storm’s deep convection is still occurring south and east of the center of circulation. This shear will abate soon, allowing Sally to become stronger and more symmetrical, and it is likely to become a hurricane early Monday.
Per NHC, current movement is west-northwest at about 9 mph. Sally is closely following its forecast trajectory across the Gulf, but doing so at a pace a few miles per hour faster than predicted at this time yesterday. This motion will continue through early Tuesday, when Sally will slow notably and pivot north as it nears far southeastern Louisiana.
Sally’s slightly faster movement over the weekend has a couple of key implications for the forecast. First, by virtue of moving farther west before steering currents weaken, Sally will have less time over water. This is good news, as moving landfall timing ahead to Tuesday takes the most alarming rapid intensification possibilities off the board.
The most aggressive intensity models have backed off, and there is now solid model consensus for peak sustained winds in the 80 to 100 mph range. This would make Sally a category 1 or 2 hurricane on the Saffir-Simpson Hurricane Wind Scale as it moves into eastern Louisiana early Tuesday, likely remaining at or near hurricane intensity as it passes near New Orleans or southern Mississippi before accelerating northeast and inland Wednesday.
The distinction between land and water in southeastern Louisiana is semantics in many places, so do not expect rapid weakening after “landfall” Tuesday.
The second forecast change since yesterday is that a westward shift moves the eastern third of Louisiana out of the relatively mild impacts expected in the western half of the storm and into potentially the worst of what Sally will bring.
Sally’s angle of approach from the south and slow forward speed are very dangerous for eastern Louisiana, as an extended period of east winds would push life-threatening surge into Lakes Pontchartrain, Maurepas, and Borgne. There is potential for a widespread 4 to 7 feet of surge in these areas, with local inundations of 10 feet or more.
Precise track matters a lot for who gets the worst of the surge in eastern Louisiana; as always, monitor local emergency management and statements from the NHC and your local National Weather Service office for details.
Additionally, the eastern third of Louisiana, including New Orleans metro, and the Mississippi Gulf Coast have the greatest chance of seeing damaging hurricane force wind gusts on Tuesday. For Lafayette and west, impacts are still expected to be modest, limited to some passing showers and gusty but not damaging winds, assuming the track does not shift further west.
Because Sally will likely be moving around 5 mph as it bends north between late Monday and early Wednesday, the most widespread danger from the storm is still likely to be widespread heavy rainfall triggering flash flooding. This danger will extend hundreds of miles east of the center of Sally, and is much less dependent on an exact track and intensity scenario playing out.
The region at highest risk of dangerous flash flooding is roughly between New Orleans and Destin, particularly close to the Gulf Coast. These areas can expect heavy rainfall to begin Monday and extend through at least Wednesday, with widespread 6-12 inch rainfall totals and possible totals up to 20 inches locally. Inland eastern Mississippi and western Alabama can also expect 5-10 inches Wednesday and Thursday.
For the Florida Panhandle, Sally’s effects will be mostly limited to off-and-on heavy rainfall through Wednesday, which be heavier and steadier the further south and west you go. Look for 5-day rainfall totals of 6-10 inches in Pensacola, Fort Walton Beach and Destin, 3-6 inches in Panama City and Apalachicola, and 2-4 inches in Tallahassee. Local totals, as always, may be higher or lower than these general expectations.
Surge across the Panhandle will run 1 to 2 feet above normal east to Apalachee Bay in association with brisk onshore flow. The Panhandle will not see damaging wind from Sally, though gusts of 40 to 55 mph along the immediate coast are likely through Tuesday in intermittent squalls, and a Tropical Storm Warning remains in effect from Indian Pass east to the Florida-Alabama border.
Bottom line is that Sally is a full-spectrum wind, surge, and rain threat to the central Gulf Coast into the midweek. While the worst-case scenarios are less likely today, all residents from central Louisiana to the Florida Panhandle should continue to closely watch Sally over the next few days and be ready to act if necessary to protect life and property, particularly given the risks of flash flooding. Keep watching the skies.
Dr. Ryan Truchelut is chief meteorologist at WeatherTiger, a Tallahassee start-up providing advanced weather and climate analytics, forensic meteorology and expert witness consulting, and agricultural and hurricane forecasting subscription services. For more information, visit us at weathertiger.com or get in touch at firstname.lastname@example.org.