[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 241454
TCDAT4

Tropical Storm Ian Discussion Number   6
NWS National Hurricane Center Miami FL       AL092022
1100 AM EDT Sat Sep 24 2022

Ian still has an asymmetric appearance in satellite imagery this
morning, with most of the deep convection located over the western
portion of the circulation. Tail Doppler radar and dropsonde data
from a NOAA Hurricane Hunter aircraft indicate the cyclone is still
vertically tilted, with the low- to mid-level center displaced to
the south of the surface center. This structure is likely a product
of the northerly shear that has affected the cyclone since genesis.
The aircraft reported 700-mb flight-level winds of 43 kt and SFMR
retrievals slightly above 35 kt, which supports keeping the initial
intensity at 40 kt for this advisory.

The initial motion is a bit south of due west at 260/13 kt. A
generally westward motion is expected through tonight as the cyclone
is steered by a narrow ridge to its north. Ian is forecast to turn
northwestward on Sunday and north-northwestward on Monday as it
moves across the northwestern Caribbean Sea around the periphery of
the ridge. The NHC track forecast during this period has been
adjusted slightly south and west of the previous one, in line with
the track consensus aids. Beyond 72 h, there is still a large amount
of cross-track spread in the guidance as Ian emerges into the
eastern Gulf of Mexico and approaches Florida. Hopefully, data
collected from special radiosonde releases beginning later today and
a scheduled NOAA G-IV flight will help resolve the steering flow
around Ian and deep-layer trough that is forecast to be over the
eastern U.S. early next week. The guidance envelope has once again
shifted westward this cycle, and the official NHC track forecast has
been adjusted in this direction as well, though it still lies
slightly to the east of the TVCA and HCCA aids. Further adjustments
to the track forecast may be needed given the increased uncertainty
in the day 3-5 period.

Ian is moving into a lower shear environment over very warm waters,
and it should not take long for the system to shed its tilted
structure and develop an inner core. Once that occurs, significant
to rapid intensification is expected while Ian crosses the
northwestern Caribbean Sea. The intensity guidance unanimously
supports strengthening during the next several days, and the
SHIPS-RII probabilities indicate a 67 percent chance of a 65-kt
intensity increase in 72 h. Therefore, the NHC track forecast has
been raised from the previous one, showing Ian becoming a hurricane
by late Sunday and approaching western Cuba at or near major
hurricane strength by Monday night. Limited land interaction is
expected as the cyclone quickly passes over western Cuba, and Ian
is forecast to be a major hurricane over the eastern Gulf of Mexico
on Tuesday and Wednesday as it approaches the west coast of Florida.

Key Messages:

1.  Ian is expected to produce heavy rainfall, flash flooding, and
possible mudslides in areas of higher terrain, particularly over
Jamaica and Cuba. Limited flash and urban flooding is possible with
rainfall across the Florida Keys and Florida peninsula through mid
next week.

2.  Hurricane conditions are possible in the Cayman Islands by early
Monday, with tropical storm conditions possible by late Sunday.
Tropical storm conditions are possible in Jamaica on
Sunday.

3.  Ian is forecast to move near or over western Cuba and approach
the west coast of the Florida peninsula at or near major hurricane
strength early next week, where there is increasing confidence in
multiple life-threatening hazards: storm surge, hurricane-force
winds and rainfall flooding. While it is too soon to determine the
exact magnitude and location of these hazards, residents in Cuba,
the Florida Keys, and the Florida peninsula should ensure they have
their hurricane plan in place, follow any advice given by local
officials, and closely monitor updates to the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 14.4N  75.2W   40 KT  45 MPH
 12H  25/0000Z 14.5N  76.8W   45 KT  50 MPH
 24H  25/1200Z 15.5N  78.9W   55 KT  65 MPH
 36H  26/0000Z 17.0N  80.7W   70 KT  80 MPH
 48H  26/1200Z 18.8N  82.3W   85 KT 100 MPH
 60H  27/0000Z 20.7N  83.4W   95 KT 110 MPH
 72H  27/1200Z 22.7N  84.1W  100 KT 115 MPH
 96H  28/1200Z 26.0N  83.9W  105 KT 120 MPH
120H  29/1200Z 28.6N  82.9W   95 KT 110 MPH

$$
Forecaster Reinhart
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