[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 242056
TCDAT4

Tropical Storm Ian Discussion Number   7
NWS National Hurricane Center Miami FL       AL092022
500 PM EDT Sat Sep 24 2022

The satellite presentation of Ian has improved this afternoon. The
associated deep convection shows increased signs of organization,
and the deep-layer shear appears to have diminished over the cyclone
based on more extensive upper-level outflow noted in visible
satellite imagery. An Air Force Hurricane Hunter aircraft found
850-mb peak flight level winds of 44 kt and several SFMR retrievals
greater than 40 kt, while dropsonde data suggest the minimum
pressure has not changed much since the previous flight. A blend of
these data support an initial intensity of 40 kt for this advisory.

The aircraft data suggest the center could be re-forming slightly
west of previous estimates, so the initial motion is an uncertain
265/14 kt. Ian is expected to move westward through early Sunday
before turning northwestward around the southwestern periphery of a
ridge to the north. A north-northwestward to northward motion is
forecast on Monday and Tuesday as the center of Ian passes near or
over the western tip of Cuba and emerges over the southeastern Gulf
of Mexico. Overall, the westward trend in the track models
continues, with the latest GFS on the far left side of the guidance
envelope and the ECMWF on the right edge. The track forecast is
still highly uncertain at days 4-5, with the GFS and ECMWF positions
about 200 n mi apart by 96 h. There is significant spread noted even
among the GFS ensemble members, with positions that range from the
north-central Gulf of Mexico to the west coast of Florida.
Hopefully, data collected from special radiosonde releases and a
NOAA G-IV flight this evening will help better resolve the steering
flow around Ian and the deep-layer trough that is forecast to be
over the eastern U.S. early next week. The latest NHC track forecast
is once again adjusted westward, and further adjustments may be
needed given the increased uncertainty in the day 3-5 period.

Ian is expected to significantly strengthen over the next few
days as it moves within a low shear environment over SSTs greater
than 30 deg C in the northwestern Caribbean Sea. As the structure
of the cyclone continues to improve and Ian develops an inner core,
rapid intensification (RI) appears very likely. The SHIPS-RII
probabilities continue to highlight this potential, with a 66
percent chance of a 65-kt intensity increase in 72 h. The NHC
intensity forecast has been raised substantially through 96 h, and
it now shows Ian reaching major hurricane strength by late Monday
before it nears western Cuba. These changes closely follow the IVCN
and HCCA consensus aids, although there remains guidance even higher
than the current forecast. Ian is forecast to remain a major
hurricane as it moves northward across the eastern Gulf of Mexico
and approaches Florida. Environmental conditions could become less
favorable late in the period due to southerly shear associated with
the aforementioned trough, but Ian is expected to remain a large
and powerful hurricane through the period.


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 or tropical storm conditions are expected on Grand
Cayman beginning early Monday.

3.  Ian is forecast to be a major hurricane when it passes near or
over western Cuba, and there is increasing confidence in a
life-threatening storm surge and hurricane-force winds in portions
of western Cuba beginning late Monday.

4. Ian is expected to remain a major hurricane when it moves
generally northward across the eastern Gulf of Mexico during the
middle of next week, but uncertainty in the track forecast is higher
than usual.  Regardless of Ian’s exact track, there is a risk of
dangerous storm surge, hurricane-force winds, and heavy rainfall
along the west coast of Florida and the Florida Panhandle by the
middle of next week, and residents in Florida 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  24/2100Z 14.3N  77.0W   40 KT  45 MPH
 12H  25/0600Z 14.6N  78.4W   50 KT  60 MPH
 24H  25/1800Z 15.7N  80.3W   60 KT  70 MPH
 36H  26/0600Z 17.4N  82.2W   75 KT  85 MPH
 48H  26/1800Z 19.2N  83.5W   95 KT 110 MPH
 60H  27/0600Z 20.9N  84.4W  110 KT 125 MPH
 72H  27/1800Z 23.1N  85.0W  115 KT 130 MPH
 96H  28/1800Z 26.2N  84.8W  115 KT 130 MPH
120H  29/1800Z 28.7N  83.9W   90 KT 105 MPH

$$
Forecaster Reinhart

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