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Hurricane Sally Special Discussion Number 20
NWS National Hurricane Center Miami FL AL192020
130 AM CDT Wed Sep 16 2020
Justification for this special advisory is to increase the
initial intensity and the 12-h forecast intensity at landfall.
Observations from an Air Force Hurricane Hunter aircraft and Mobile
Alabama WSR-88D Doppler radar data indicate that Sally has continued
to strengthen this morning. Radar data show that Sally's eye has
become better defined and Doppler velocities in the northern eyewall
have reached average values of at least 110 kt between 5000-6000 ft
ASL, which supports an equivalent surface wind speed of about 89 kt.
The reconnaissance aircraft has recently measured peak 700-mb
flight-level winds of 103 kt, which equates to about 93 kt using a
standard 90 percent adjustment factor, while peak SFMR surface wind
speed have been 85 kt. In addition, a recent dropsonde in the
northeast eyewall measured an average wind speed of 113 kt in the
lowest 150 meters, which equates to about a 94-kt surface wind.
However, those winds appeared to be possibly contaminated by wind
gusts. Based on the above data, the initial intensity has been
increased to 90 kt.
Some additional slight strengthening is possible until landfall
occur, and Sally could peak at 95 kt. Rapid weakening will occur
after the center moves inland, and the system should become a
remnant low in a couple of days. This is consistent with the
latest model guidance.
Radar and aircraft center fixes indicate that Sally's motion is
north-northeastward, or 030/02 kt. No changes were made to the
previous track forecast. Sally should continue to move
north-northeastward this morning, and then turn northeastward with
a gradual increase in forward speed by tonight. That motion will
then continue for the next day or so. Then, as Sally approaches the
westerly flow at higher latitudes, the cyclone should turn toward
the east-northeast with a slight further increase in forward speed
until becoming a dissipating remnant low near the southeast U.S.
coast in 2-3 days. The official forecast is close to the latest
corrected dynamical model consensus, HCCA, prediction.
1. Historic, life-threatening flash flooding due to rainfall is
likely through Wednesday along and just inland of the coast from the
Florida Panhandle west of the Apalachicola River to the
Alabama/Mississippi border. Widespread moderate to major river
flooding is forecast across the Florida Panhandle and southern
Alabama. Significant flash and urban flooding, as well as
widespread minor to moderate river flooding, is likely across inland
portions of Mississippi and Alabama, and into Georgia and the
western Carolinas this week.
2. Life-threatening storm surge is expected along portions of the
coastline from Alabama to the western Florida Panhandle, including
3. Hurricane conditions are expected this morning and then continue
into this afternoon within portions of the Hurricane Warning area
along the Mississippi and Alabama coastlines and the western Florida
FORECAST POSITIONS AND MAX WINDS
INIT 16/0630Z 29.9N 87.8W 90 KT 105 MPH
12H 16/1200Z 30.3N 87.5W 95 KT 110 MPH
24H 17/0000Z 31.2N 86.8W 40 KT 45 MPH...INLAND
36H 17/1200Z 32.0N 85.7W 30 KT 35 MPH...INLAND
48H 18/0000Z 32.9N 83.9W 25 KT 30 MPH...INLAND
60H 18/1200Z 33.6N 81.5W 20 KT 25 MPH...INLAND
72H 19/0000Z 34.0N 79.0W 20 KT 25 MPH...POST-TROP/REMNT LOW