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ropical Storm Sally Discussion Number 10
NWS National Hurricane Center Miami FL AL192020
1000 PM CDT Sun Sep 13 2020

Sally is gradually getting better organized. Satellite images show
that deep convection has increased near the center, and the cyclone
is now a little more symmetric and vertically aligned compared to
earlier today. The Air Force Hurricane Hunters are currently
investigating Sally, and so far they have found maximum 850-mb
flight-level winds of 54 kt and maximum believable SFMR winds of 49
kt, which support the 50-kt initial intensity.

Reports from the aircraft indicate that the center of Sally has
jogged to the northeast, with the latest 12-hour motion estimated to
be 305/7 kt. The global models show a trough exiting the northeast
U.S. tomorrow and a ridge building to the north of Sally, which
should cause the storm to resume a west-northwest motion at a
relatively slow pace on Monday. By Monday night and Tuesday, the
ridge is forecast to slide southeastward as another trough develops
over the south-central U.S. This change in the pattern should cause
Sally to slow down even more and gradually turn to the north and
then the northeast. The new NHC tack forecast is slower and east
of the previous one based on the initial position/motion and the
latest models. However, the official forecast still lies west of
the latest consensus aids, so further adjustments may be necessary
overnight. While the current forecast shows landfall along the
northern Gulf coast in 36 to 48 hours, the bottom line is that Sally
is expected to be a slow- moving tropical cyclone near and over the
northern Gulf Coast during the next few days.

The upper-level low that was producing northwesterly shear over
Sally is moving away, resulting in a more favorable upper-level wind
pattern for strengthening. These more conducive winds aloft
combined with the very warm Gulf of Mexico waters and a moist air
mass should allow the cyclone to steadily strengthening until
Sally crosses the coast in 36 to 48 hours. The NHC intensity
forecast is largely an update of the previous one and lies near the
high end of the model guidance. After landfall, rapid weakening is
forecast, and Sally is expected to become a tropical depression by
72 hours and dissipate in about 5 days.

The eastward shift in the track forecast necessitates the extension
of the hurricane warning eastward to the Mississippi/Alabama
border.

KEY MESSAGES:

1. It is too early to determine where Sally’s center will move
onshore given the uncertainty in the timing and location of Sally’s
northward turn near the central Gulf Coast. Users should not focus
on the details of the official forecast track, since NHC’s average
forecast error at 48 hours is around 80 miles, and dangerous storm
surge, rainfall, and wind hazards will extend well away from the
center.

2. An extremely dangerous and life-threatening storm surge is
expected for areas outside the southeastern Louisiana Hurricane and
Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to
the Alabama/Florida border, where a Storm Surge Warning is in
effect. Residents in these areas should follow any advice given by
local officials.

3. Hurricane conditions are expected by late Monday within portions
of the Hurricane Warning area from Morgan City, Louisiana, to
the Mississippi/Alabama border, including Metropolitan New Orleans,
with tropical storm conditions likely to begin Monday. Preparations
should be rushed to completion in those areas.

4. Sally could continue to produce flash flooding across central and
northern Florida and prolong existing minor river flooding across
west-central Florida through Monday. Widespread significant flash
flooding and minor to isolated major river flooding is likely across
southeastern Louisiana, Mississippi, and Alabama through the middle
of the week. Flooding impacts are expected to spread farther across
the Southeast U.S. through the week.

FORECAST POSITIONS AND MAX WINDS

INIT 14/0300Z 28.2N 86.2W 50 KT 60 MPH
12H 14/1200Z 28.6N 87.3W 60 KT 70 MPH
24H 15/0000Z 29.0N 88.3W 70 KT 80 MPH
36H 15/1200Z 29.4N 89.0W 80 KT 90 MPH
48H 16/0000Z 30.3N 89.4W 70 KT 80 MPH...INLAND
60H 16/1200Z 31.2N 89.1W 45 KT 50 MPH...INLAND
72H 17/0000Z 32.1N 88.3W 30 KT 35 MPH...INLAND
96H 18/0000Z 33.6N 85.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 19/0000Z...DISSIPATED