Atlantic Basin Tropical Cyclones

Tropical Storm Ian Forecast Discussion


000
WTNT44 KNHC 252057
TCDAT4

Tropical Storm Ian Discussion Number  11
NWS National Hurricane Center Miami FL       AL092022
500 PM EDT Sun Sep 25 2022

The organization of Ian has not changed much since this morning. 
There have been some small bursts of convection closer to the center 
of the storm this afternoon, but the activity has not yet led to any 
notable changes in its structure. In fact, the most persistent 
convection has been in outer rainbands well to the northeast of the 
circulation near Jamaica. The SFMR wind data and adjusted 
flight-level winds from the earlier reconnaissance flights supported 
surface winds of 35-40 kt, and the initial intensity is set at 40 kt 
for this advisory. A NOAA Hurricane Hunter aircraft is scheduled to 
investigate Ian later tonight. 

The center of Ian has jogged a bit northward this afternoon, but its 
longer-term motion is west-northwestward at 300/10 kt. A generally 
northwestward motion is expected tonight, followed by a 
north-northwestward motion on Monday and early Tuesday as it moves 
across the northwestern Caribbean Sea and near or over western Cuba. 
From there, the track guidance still diverges at days 3-5 as Ian is 
forecast to move northward across the eastern Gulf of Mexico. The 
ECMWF and UKMET models still lie on the eastern edge of the guidance 
and bring the center of Ian over the coast of west-central Florida, 
while the HWRF and HMON models are on the western side of the 
envelope and show Ian approaching the central Florida panhandle. 
Notably, the GFS has trended slightly eastward for the past few 
cycles, which has brought the multi-model consensus aids a bit 
eastward as well. The latest NHC track forecast has been adjusted in 
this direction, but only on the order of 15-20 n mi in the extended 
range. Users are reminded not to focus on the details of the track 
forecast at longer time ranges, since uncertainty is still high and 
future adjustments may be required.

Although the storm has yet to develop an inner core, the conditions 
over the northwestern Caribbean Sea appear very likely to support 
strengthening once it becomes better organized. Some dry 
environmental air may have limited convection today, but the GFS- 
and ECMWF-simulated satellite imagery indicate that deep convection 
will increase during the diurnal maximum period overnight. Then, 
significant strengthening is expected with low deep-layer shear and 
high oceanic heat content along the forecast track. There is still 
strong support for rapid intensification in the latest intensity 
guidance, and the NHC intensity forecast shows Ian becoming a 
hurricane on Monday and a major hurricane on Tuesday. This forecast 
remains close to the IVCN multi-model consensus, with some model 
aids including HCCA showing even higher peak intensities. Strong 
southwesterly shear develops over Ian by 72 h related to interaction 
with an upper-level trough, and the structure of the cyclone could 
significantly degrade before landfall given these hostile 
conditions. However, Ian is likely to have an expanding wind field 
and will be slowing down by that time, which will have the potential 
to produce significant wind and storm surge impacts across portions 
of the Florida west coast and the Florida panhandle.


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.  Flash and urban flooding is possible with 
rainfall across the Florida Keys and the Florida peninsula through 
the middle of the week. Additional flooding on rivers across 
northern Florida and parts of the southeast U.S. cannot be ruled out 
later this week. 

2.  Life-threatening storm surge and hurricane-force winds are 
expected in portions of western Cuba beginning late Monday, and Ian 
is forecast to be at or near major hurricane strength when it is 
near western Cuba. Efforts to protect life and property should be 
rushed to completion. 

3.  Ian is expected to be a major hurricane in the eastern Gulf of 
Mexico during the middle of this week, but uncertainty in the track 
and intensity forecasts remains higher than usual. Regardless of 
Ian’s exact track and intensity, 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 this 
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  25/2100Z 16.2N  80.3W   40 KT  45 MPH
 12H  26/0600Z 17.3N  81.5W   50 KT  60 MPH
 24H  26/1800Z 19.2N  82.9W   70 KT  80 MPH
 36H  27/0600Z 21.1N  83.7W   90 KT 105 MPH
 48H  27/1800Z 23.0N  84.2W  105 KT 120 MPH
 60H  28/0600Z 24.8N  84.4W  115 KT 130 MPH
 72H  28/1800Z 26.2N  84.4W  110 KT 125 MPH
 96H  29/1800Z 28.3N  84.0W   85 KT 100 MPH
120H  30/1800Z 31.0N  83.0W   50 KT  60 MPH...INLAND

$$
Forecaster Reinhart



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