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Tropical Storm SALLY

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.

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
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. 

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