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Hurricane Sally Discussion Number  17
NWS National Hurricane Center Miami FL       AL192020
1000 AM CDT Tue Sep 15 2020
 
The satellite presentation of Sally has not changed much since
overnight. A ragged eye is seen in WSR-88D radar imagery, with
a band occasionally trying to wrap around the southwestern side.
A NOAA reconnaissance aircraft has just recently provided a new 
center fix, and data from the center drop indicated the minimum 
pressure is 983 mb.  The first pass through the northeastern 
quadrant suggests that the 50-kt wind field may have expanded, but 
there has been little change in peak winds reported by the 
aircraft.  The intensity has been held at 75 kt pending additional 
data from the NOAA P-3 mission that has just begun.  A highly 
elevated oil rig just northeast of the center reported peak has 
reported sustained winds of 69 kt with a gust to 86 kt around 1200 
UTC this morning.
 
Sally has been meandering this morning, but the longer-term motion 
is northwestward or 315/2 kt. Sally remains within an area of weak
steering flow, but a weak mid-level trough over the south-central
United States is forecast to slide eastward over the next over the
next couple of days. This pattern should cause Sally to move very
slowly north-northwestward to northward over the next 24 hours, with
the center of the hurricane nearing the northern Gulf Coast late
tonight or Wednesday. By late Wednesday, Sally should turn
northeastward as the aforementioned trough approaches Missouri and
Arkansas. The new forecast has been nudged slightly eastward in 
the early portion of the track forecast, but the latter portion is 
very close to the previous advisory.  The new track lies a little 
to the west of the various consensus aids in deference to the 
typically reliable GFS and ECMWF models that are near the left
edge of the guidance envelope.  Sally's forward motion is forecast
to be around 5 kt or less throughout the forecast period, which
will result in a long period of heavy rainfall and historic flooding
along the north-central Gulf Coast.
 
Moderate westerly shear and upwelling beneath the slow moving
hurricane are likely to prevent strengthening today.  The shear is
forecast to increase tonight and although some slight weakening
could occur before the center reaches the coast, Sally is predicted
to remain a dangerous hurricane through landfall.  Once Sally moves
inland, rapid weakening is expected and circulation is forecast to
lose definition and dissipate by day 4.
 
Users are reminded to not focus on the specific timing and location 
of landfall.  Life-threatening storm surge, historic flash flooding 
from heavy rainfall, and dangerous winds will affect a large portion 
of the north-central Gulf Coast during the next few days.
 
KEY MESSAGES:
 
1. Life-threatening storm surge is expected from the Mouth of the
Mississippi River to the Okaloosa/Walton County Line in the Florida
Panhandle. The highest inundation is expected along the Alabama
coast, including Mobile Bay.
 
2. Historic life-threatening flash flooding is likely through 
Wednesday along and just inland of the coast from the western 
Florida Panhandle to far southeastern Mississippi. Widespread 
moderate to major river flooding is forecast along and just inland 
of the central Gulf Coast. Significant flash and urban flooding, as 
well as widespread minor to moderate river flooding, are likely 
across inland portions of Mississippi, Alabama, northern Georgia, 
and the western Carolinas through the week.
 
3. Hurricane conditions are expected today within portions of the
Hurricane Warning area along the Mississippi and Alabama coastlines
and the western Florida Panhandle.

FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 29.1N  88.2W   75 KT  85 MPH
 12H  16/0000Z 29.6N  88.2W   75 KT  85 MPH
 24H  16/1200Z 30.2N  88.1W   70 KT  80 MPH
 36H  17/0000Z 31.0N  87.6W   55 KT  65 MPH...INLAND
 48H  17/1200Z 31.9N  86.6W   35 KT  40 MPH...INLAND
 60H  18/0000Z 32.6N  85.2W   25 KT  30 MPH...INLAND
 72H  18/1200Z 33.0N  83.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  19/1200Z...DISSIPATED
 
$$
Forecaster Brown
 
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