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#1016651 (Received by flhurricane at: 10:53 AM 14.Sep.2020)
TCDAT4

Tropical Storm Sally Discussion Number 12
NWS National Hurricane Center Miami FL AL192020
1000 AM CDT Mon Sep 14 2020

An intense burst of deep convection with cloud tops colder than -80
degrees Celsius has developed over and the to east of the center
this morning. A recent fix from an Air Force Reserve Hurricane
Hunter aircraft indicates that the center has reformed to the
east of the previous estimated location, beneath the burst of
deep convection. NWS WSR-88D radar imagery shows an increase in
banding around the eastern and southeastern portion of new center
found by the aircraft and it appears that an eye is in its formative
stage. The aircraft has reported believable SFMR winds of 55 kt, and
that is the basis for the initial intensity. The most recent
minimum pressure estimated from the aircraft data is 991 mb, down
several millibars from the first fix on this flight.

Sally is located within a conducive environment of low wind shear,
warm waters, and a moist atmosphere. These conditions are likely to
lead to steady strengthening over the next 24 hours or so. With the
recent increase in organization of the inner core, there is more
confidence that Sally will strengthen to a hurricane later today or
tonight. Additional strengthening is possible on Tuesday while the
storm moves slowly northwestward near the coast of southeast
Louisiana. Increasing westerly wind shear and land interaction will
probably slow the intensification rate by late tomorrow. The new
NHC intensity forecast is similar to the previous advisory and is
near the upper-end of the guidance envelope. Since Sally is
forecast to be moving very slowly around the time of landfall a
slower rate of weakening is indicated since a large portion of the
circulation will remain over water for some time.

Given the recent re-formation of the center, the initial motion is a
somewhat uncertain west-northwestward at 5 kt. Weak ridging over
the southeastern United State should steer Sally slowly west-
northwestward through tonight. After that time, a northwestward to
northward turn is anticipated but the exact timing and location of
the turn remains uncertain. The general trend in the guidance has
been eastward for the past few cycles, and the NHC forecast has been
nudged in that direction and lies between the GFS and ECMWF models
but a little west of the various consensus aids.

Regardless of the exact forecast track and intensity of Sally,
the slow-moving storm is expected to cause a life-threatening storm
surge and freshwater flooding event.

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 tonight within the Hurricane
Warning area in southeastern Louisiana and are expected by late
Tuesday within the Hurricane Warning area along the Mississippi and
Alabama coastline. Tropical storm conditions are likely to begin
later today and this evening in these areas and preparations
should be rushed to completion.

4. Life-threatening flash flooding is likely, as well as widespread
minor to isolated major flooding, on area rivers along and just
inland of the Central Gulf Coast. Significant flash and urban
flooding, as well as widespread minor to moderate river flooding is
likely across Mississippi and Alabama through the middle of the
week. Flooding impacts are expected to spread farther across the
Southeast through the week. Sally could continue to produce flash
flooding across the Florida peninsula and prolong existing minor
river flooding across west-central Florida through today.

FORECAST POSITIONS AND MAX WINDS

INIT 14/1500Z 28.4N 86.9W 55 KT 65 MPH
12H 15/0000Z 28.7N 88.0W 65 KT 75 MPH
24H 15/1200Z 29.2N 88.8W 75 KT 85 MPH
36H 16/0000Z 29.8N 89.1W 80 KT 90 MPH
48H 16/1200Z 30.8N 88.7W 60 KT 70 MPH...INLAND
60H 17/0000Z 31.8N 87.7W 30 KT 35 MPH...INLAND
72H 17/1200Z 32.6N 86.5W 25 KT 30 MPH...INLAND
96H 18/1200Z 33.1N 84.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 19/1200Z...DISSIPATED

$$
Forecaster Brown