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Tropical Storm Sally Discussion Number  11...Corrected
NWS National Hurricane Center Miami FL       AL192020
400 AM CDT Mon Sep 14 2020

Corrected 4th Key Message

The organization of Sally hasn't changed much during the past 
several hours.  While there was a large burst of convection 
earlier, it did not translate into any intensification, with 
flight-level reconnaissance and SFMR surface winds still supporting 
an initial wind speed of 50 kt.  The Air Force Reserve plane did 
find that the size of tropical-storm-force wind field has 
notable grown to the north and northwest of the center.  The storm 
still has time to intensify under a seemingly conducive environment 
during the next 24-36 hours, before a combination of increasing 
westerly wind shear and land interaction will probably slow the 
intensification rate. Model guidance has come down slightly from 6 
hours ago, but it has been inconsistent from cycle to cycle.  The 
new intensity forecast is similar to the previous one and lies near 
the top end of the guidance envelope.

The reconnaissance plane showed that Sally took a westward turn 
during the past several hours, but the storm appears to have a 
resumed a more west-northwestward motion recently.  Weak ridging 
over the southern United States is expected to cause this general 
motion with a decrease in forward speed today before the storm 
slowly turns northward sometime on Tuesday due to an approaching 
trough.  Guidance is not in good agreement on exactly when that 
turn occurs, causing a good deal of spread for a relatively 
short-range forecast.  The track forecast has been shifted to the 
left in the short-term primarily due to the initial position, 
showing a track near or over extreme southeastern Louisiana, then 
is the near the previous one at its final landfall.  The bottom 
line continues to be that Sally is expected to be a dangerous 
slow-moving hurricane near the coast of southeastern Louisiana, 
Mississippi and Alabama during the next 2-3 days.
 
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 today 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 by late this 
morning. Preparations should be rushed to completion in those areas.
 
4. Sally may continue to produce flash flooding across the Florida 
peninsula and prolong existing minor river flooding across 
west-central Florida through today. Life-threatening flash flooding 
is possible and widespread minor to isolated major flooding on area 
rivers is likely 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.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  14/0900Z 28.3N  87.3W   50 KT  60 MPH
 12H  14/1800Z 28.6N  88.1W   60 KT  70 MPH
 24H  15/0600Z 29.1N  88.9W   70 KT  80 MPH
 36H  15/1800Z 29.7N  89.3W   75 KT  85 MPH
 48H  16/0600Z 30.6N  89.2W   60 KT  70 MPH...INLAND
 60H  16/1800Z 31.6N  88.6W   30 KT  35 MPH...INLAND
 72H  17/0600Z 32.5N  87.6W   25 KT  30 MPH...INLAND
 96H  18/0600Z 33.5N  85.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  19/0600Z...DISSIPATED
 
$$
Forecaster Blake
 
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