Sally Will Be An Immense Extreme Rainfall Event

96L Likely A Northern Gulf of Mexico Tropical Cyclone Early Next Week
09/11/2020, 10:48 am EDT
Emerging New Issue in the Gulf of Mexico
09/16/2020, 1:48 pm EDT
Show all

Highlight: NOAA/NHC adjusts Sally forecast track slightly east – two landfalls likely. An extreme rainfall producer!

Fig. 1: Satellite picture of the Gulf of Mexico reveals the strengthening massive amount of convection associated with Sally destined to bring extreme rain to the central/northeast Gulf States.

Fig. 2: The immense rainfall forecast by NOAA/NHC due to slow-moving Sally.

Fig. 3: The NOAA/NHC potential storm surge associated with Sally. Water rise based on the SLOSH model is annotated.

Fig. 4: The NOAA/NHC Sally forecast track indicates a southeast Louisiana landfall as a hurricane late tonight and southwest Mississippi late Tuesday.

Fig. 5-6: The NOAA/NHC tropical storm and hurricane force probability profiles.

Fig. 7: The tropical cyclone model intensity forecasts for Sally.

Discussion: At 5AM EDT Tropical Storm Sally was located at 28.3N/87.3W or about 120 miles east-southeast of the mouth of the Mississippi River. Sally is moving west-northwest at 9 mph with top wind 60 mph and central pressure 996 MB.

Sally is slowly organizing in that the associated convection is becoming more concentric. The interaction between the convection east of Sally and the Florida coastline has eased and dry air entrainment off the Yucatan Peninsula has also dissipated. Northwest shear across Salley is still present but weaker. The environment improves as Sally shifts west and west-northwest and intensification to a hurricane is likely today.

Forecast models turn Sally to the north more quickly causing the storm to make two landfalls on coastal southeast Louisiana tonight and southwest Mississippi late tomorrow. Sally should easily reach category-1 hurricane status and still has a chance to become a category-2 hurricane while very close to the north-central Gulf of Mexico coast. A category-3 major hurricane is not expected.

Sally is a slow-mover and the largest concern with this storm is the rainfall profile. 24-36 hour heavy rainfall is likely for the north-central Gulf coast most focused on coastal Mississippi where the right-front quadrant of the storm brings the most dangerous weather. Rainfall amounts of 4-8 in. will extend to the southern Appalachians as Sally drifts inland and weakens.

The storm surge forecast by NOAA/NHC is unchanged from yesterday. However, the SLOSH model indicates the highest water rise (6 feet) is most focused on the lower Mississippi River and Mississippi Coast.

Tropical storm force wind will extend well inland with Sally while hurricane force wind affects coastal southeast Louisiana and coastal Mississippi.

Sally has been wobbling sometimes due west overnight so while the forecast track is slightly east of yesterday there remains a chance at further adjustments with today’s forecast.