[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 272059
TCDAT4

Hurricane Ian Discussion Number  19
NWS National Hurricane Center Miami FL       AL092022
500 PM EDT Tue Sep 27 2022

The pressure on the last Air Force Hurricane Hunter aircraft fix
fell to about 952 mb, indicating that Ian is restrengthening
over the southeastern Gulf of Mexico.  The eye of Ian remains
well-defined on visible imagery, although radar data from Key West
suggest that an eyewall replacement could be in the initial stages.
The initial wind speed is set to 105 kt, matching a blend of
earlier SFMR and flight-level wind data.  The plane data also
showed that the area of hurricane-force winds is growing on the
east side of the cyclone.

Ian is moving east-of-due-north, or 010/9-kt, with occasional
wobbles to the north-northeast.  A track toward the north-northeast
is expected for the next couple of days while it moves between a
ridge over the Bahamas and a trough over the western Gulf of Mexico.
There has been some model convergence this afternoon showing Ian
remaining stronger and vertically deeper through landfall.  This
solution results in a faster track, again adjusted to the southeast,
and the new forecast is moved in that direction. This new NHC track
is close to the corrected model consensus and between the quicker
ECMWF and slower GFS models.  It should be emphasized that this
track remains uncertain, with a typical spread in the steering
features leading to big speed and track differences down the line,
not to mention the oblique angle of approach to Florida. In a few
days, more of the guidance is showing Ian interacting with a
shortwave trough over the southeastern United States, causing the
system to move back over the northwestern Atlantic in the longer
range, before turning northwestward back over land.  The day 3-5
track forecast is also shifted eastward, although significant
re-strengthening is not expected at long range.

The outflow pattern of the hurricane is beginning to be impinged
upon in the southwestern quadrant, a sign that upper-level
southwesterly flow is starting to affect the outer circulation.
While the shear should increase up through landfall, it is just too
close-to-call whether it starts to weaken Ian or not, or whether the
larger system is able to resist the shear.  Additionally, an eyewall
replacement cycle could be in its initial phases, although
predicting these structural changes is extremely difficult.  The new
forecast is near the last one, a little higher than the consensus.
I should note that whether Ian comes ashore as category 4 hurricane
or a large category 3 after an eyewall cycle, avoiding a large and
destructive hurricane for Florida seems very unlikely, and residents
should heed the advice of local emergency management officials.

The new forecast necessitates a Hurricane Warning for portions of
extreme southwestern Florida, and a Tropical Storm Warning for the
rest of southeastern Florida that wasn't previously under a warning.
Users are reminded to not focus on the exact track as some
additional adjustments to the track are possible. Significant wind,
storm surge, and rainfall hazards will extend far from the center.


Key Messages:

1. Life-threatening storm surge is increasingly likely along the
Florida west coast where a storm surge warning is in effect, with
the highest risk from Naples to the Sarasota region. Residents in
these areas should listen to advice given by local officials and
follow any evacuation orders for your area.

2. Hurricane-force winds are expected in the hurricane warning area
in southwest and west-central Florida beginning Wednesday morning
with tropical storm conditions expected overnight.  Devastating wind
damage is expected near the core of Ian. Residents should rush all
preparations to completion.

3. Heavy rainfall will affect most of the Florida Peninsula for the
next several days, spreading to the rest of the Southeast U.S. by
Thursday and Friday, likely causing flash, urban, and small stream
flooding. Considerable flooding is expected with widespread,
prolonged moderate to major river flooding expected across central
Florida.


FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 24.0N  83.2W  105 KT 120 MPH
 12H  28/0600Z 25.3N  82.9W  115 KT 130 MPH
 24H  28/1800Z 26.6N  82.5W  115 KT 130 MPH
 36H  29/0600Z 27.6N  82.0W   70 KT  80 MPH...INLAND
 48H  29/1800Z 28.5N  81.5W   55 KT  65 MPH...INLAND
 60H  30/0600Z 29.4N  81.2W   45 KT  50 MPH...INLAND
 72H  30/1800Z 31.0N  81.1W   45 KT  50 MPH...OVER WATER
 96H  01/1800Z 34.5N  82.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
120H  02/1800Z...DISSIPATED

$$
Forecaster Blake
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