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Tropical Storm Sally Discussion Number   7...Corrected
NWS National Hurricane Center Miami FL       AL192020
500 AM EDT Sun Sep 13 2020

Corrected for inland status at 60 and 72 hourrs

A large burst of convection has formed near the center of Sally this 
morning, and Air Force Reserve Hurricane Hunter data indicate that 
the storm is strengthening.  Peak flight-level winds were up to 57 
kt at 925 mb, with believable SFMR winds of up to 45 kt, and 
pressure falling a couple of mb to 1001.  The initial wind speed is 
set to 45 kt for this advisory.
 
While northwesterly shear has been affecting Sally, the global 
models suggest that the shear will decrease later today as it moves 
under a narrow ridge.  Models all respond to these changing 
conditions by showing intensification, but they disagree on the rate 
of change.  It is an extremely tricky forecast because of how this 
might happen close to landfall, but guidance is generally 5-10 kt 
higher than the last cycle so the intensity forecast has been raised 
by those amounts up through landfall.  It is worth noting that rapid 
intensification is a possibility if the system develops a more solid 
inner core on Monday, and stronger solutions like the HWRF model 
can't be dismissed.
 
Sally is moving west-northwestward at a faster speed this morning.
The biggest change to note is that almost every model has shifted
westward (faster) due to narrow ridging developing across the 
northern Gulf Coast between the storm and an exiting mid-latitude 
trough.  The flow gets quite weak near and after landfall, so the 
cyclone should slow down on Tuesday/Wednesday and turn northward. 
After that time, the next trough should induce a faster 
northeastward motion by day 5. The new track is shifted westward 
between 30-45 n mi near the coast of Louisiana, and is still east of 
the GFS and ECMWF models.  
 
Users are reminded to not focus on the exact details of the track
or intensity forecasts, as the average NHC track error at 48 h is
around 80-90 miles and the average intensity error is around 10-15
mph. In addition, wind, storm surge, and rainfall hazards will
extend far from the center. Unfortunately, confidence is increasing
that Sally's expected slow forward speed near the Gulf Coast will
exacerbate the storm surge and heavy rainfall threats.
 
KEY MESSAGES:
 
1. An extremely dangerous and life-threatening storm surge is now 
expected, and a Storm Surge Warning is in effect for areas outside 
the southeastern Louisiana Hurricane and Storm Damage Risk Reduction 
System from Port Fourchon Louisiana to the Mississippi/Alabama 
border. Residents in these areas should follow any advice given by 
local officials.
 
2. Hurricane conditions are expected by early Tuesday from Grand
Isle, Louisiana to Ocean Springs, Mississippi, including
Metropolitan New Orleans, with tropical storm conditions likely by
Monday.  Preparations should be rushed to completion in those areas.
 
3. Tropical Storm Sally is expected to produce flash flooding across 
southern and central Florida and prolong existing minor river 
flooding across Central Florida through Monday. Significant flash 
flooding and minor to isolated major river flooding is likely across 
portions of the Central Gulf Coast from Monday through the middle of 
the week.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 27.0N  84.0W   45 KT  50 MPH
 12H  13/1800Z 27.7N  85.4W   50 KT  60 MPH
 24H  14/0600Z 28.3N  87.2W   60 KT  70 MPH
 36H  14/1800Z 28.7N  88.7W   70 KT  80 MPH
 48H  15/0600Z 29.2N  89.7W   85 KT 100 MPH
 60H  15/1800Z 30.1N  90.0W   70 KT  80 MPH...INLAND
 72H  16/0600Z 31.0N  90.0W   50 KT  60 MPH...INLAND
 96H  17/0600Z 32.8N  88.6W   30 KT  35 MPH...INLAND
120H  18/0600Z 34.5N  84.5W   20 KT  25 MPH...INLAND
 
$$
Forecaster Blake
 
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