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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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