[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 281057
TCDAT4

Hurricane Ian Special Discussion Number  23
NWS National Hurricane Center Miami FL       AL092022
700 AM EDT Wed Sep 28 2022

This special advisory is being issued to update Ian's current and
forecast intensity.  Recent NOAA and Air Force Reserve Hurricane
Hunter flight-level winds are as high as 160 kt, with SFMR data
around 135 kt, with a central pressure down to 937 mb.  This
supports a current intensity of 135 kt.

The forecast intensity is raised to 135 kt at landfall, and we are
now forecasting a catastrophic storm surge of 12 to 16 ft from
Englewood to Bonita Beach, Florida.  No other significant changes
were made to the forecast.

Previous discussion --

Ian completed an eyewall replacement cycle during the overnight
hours, and very recent data from an Air Force Reserve Hurricane
Hunter aircraft indicate that the hurricane has reached category 4
intensity.  The plane reported that the central pressure has fallen
to 942 mb, down about 10 mb from around midnight.  The plane
measured a peak 700-mb flight-level wind of 141 kt, and an SFMR
wind of 109 kt.  A blend of the 700-mb reduced wind and the SFMR
yields an initial intensity of 120 kt.  Although there is some
moderate shear over the hurricane, this is not likely to affect Ian
very much due to its large size. Some fluctuations in intensity are
possible before the center reaches the coast later today, but Ian is
expected to reach the coast as an extremely dangerous category 4
hurricane.  Weakening is expected while Ian moves over the Florida
peninsula.

Ian has jogged a little to the left this morning, but the
longer-term motion remains north-northeastward or 015 degrees
at 9 kt.  The hurricane should continue moving north-northeastward
through Thursday between the western side of a subtropical ridge
and a broad trough over the eastern United States. This motion is
expected to bring the center of Ian onshore along the west coast of
Florida later today, and over central Florida tonight and Thursday.
A shortwave trough that is forecast to move southward toward the
northwestern Gulf in about 24 to 36 hours is expected to sharpen
the trough over the eastern U.S. causing Ian to turn northward
along coast of northeastern Florida and Georgia Thursday night and
Friday.  The model envelope did not change much this cycle, and very
little cross-track adjustments were needed to the official
forecast.  The GFS and ECWMF are noticeably slower than the
remainder of the dynamical models, and the updated NHC track
forecast is a little slower than the previous advisory and slightly
slower than the TVCA consensus aid out of respect for those models.


Key Messages:

1. Catastrophic storm surge inundation of 12 to 16 feet above ground
level along with destructive waves are expected somewhere along the
southwest Florida coastline from Englewood to Bonita Beach,
including Charlotte Harbor. Residents in these areas should urgently
follow any evacuation orders in effect.

2. Catastrophic wind damage is expected along the southwestern
coast of Florida beginning in the next few hours where the core of
Ian makes landfall.  Preparations to protect life and property
should be urgently rushed to completion.

3. Heavy rainfall will spread across the Florida peninsula through
Thursday and reach portions of the Southeast U.S. later this week
and this weekend.  Widespread, life-threatening catastrophic
flooding is expected across portions of central Florida with
considerable flooding in southern Florida, northern Florida,
southeastern Georgia and coastal South Carolina. Widespread,
prolonged major and record river flooding expected across central
Florida.


FORECAST POSITIONS AND MAX WINDS

INIT  28/1100Z 25.9N  82.8W  135 KT 155 MPH
 12H  28/1800Z 26.7N  82.4W  135 KT 155 MPH
 24H  29/0600Z 27.7N  81.7W   80 KT  90 MPH...INLAND
 36H  29/1800Z 28.7N  81.1W   50 KT  60 MPH...INLAND
 48H  30/0600Z 29.8N  80.7W   45 KT  50 MPH...OVER WATER
 60H  30/1800Z 31.6N  80.8W   45 KT  50 MPH
 72H  01/0600Z 33.6N  81.4W   30 KT  35 MPH...INLAND
 96H  02/0600Z 36.1N  82.1W   25 KT  30 MPH...POST-TROP/INLAND
120H  03/0600Z...DISSIPATED

$$
Forecaster Blake
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