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Tropical Storm Ian Forecast Discussion


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WTNT44 KNHC 290859
TCDAT4

Tropical Storm Ian Discussion Number  27
NWS National Hurricane Center Miami FL       AL092022
500 AM EDT Thu Sep 29 2022

Ian's center continues to move northeastward across central Florida, 
and nearly all of the heavy rains are located to the north over 
northeastern Florida.  NWS WSR-88D Doppler velocities from the
Melbourne and Tampa radars have decreased significantly since last
evening, and based on that data, Ian is now a tropical storm with 
maximum sustained winds of 55 kt.  This intensity is also supported 
by wind observations across Florida, with the highest recent 
sustained wind being 52 kt at New Smyrna Beach.

Ian's current motion is northeastward, or 040/7 kt.  The tail end 
of a deep-layer trough is expected to detach from the main trough 
axis over the southeastern United States during the next 24 to 48 
hours, and Ian is forecast to move around the eastern periphery of 
this feature, turning north-northeastward later today and then 
north-northwestward by Friday night.  In this scenario, Ian should 
move off the east coast of Florida later today, and then swing 
northward toward the South Carolina coast during the next 36 hours 
or so.  Although there is some cross-track spread in the guidance, 
they all agree on this general scenario, and the NHC track forecast 
lies where most of the models are packed.  No significant changes 
were made to the previous prediction.

Little change in intensity is forecast during the next 24 hours or 
so, mainly due to strong southwesterly shear.  After 24 hours, 
global models are suggesting that Ian could have some favorable 
interaction with the eastern U.S. trough, all while it's moving 
over the warm 28-29 degree Celsius waters of the Gulf Stream.  As a 
result, some slight strengthening is indicated in the official 
forecast by 36 hours, and Ian could be near hurricane intensity as 
it's approaching the coast of South Carolina.  This possibility is 
accounted for by the Hurricane Watch that is effect for the area.  
After moving inland, Ian is expected to weaken quickly, and global 
models indicate it should dissipate or become absorbed by another 
broader area of low pressure over the Carolinas by day 3.


Key Messages:

1. Coastal water levels continue to subside along the west coast of 
Florida.  There is a danger of life-threatening storm surge today 
through Friday along the coasts of northeast Florida, Georgia, 
and South Carolina.  Residents in these areas should follow any 
advice given by local officials.

2. Tropical-storm-force winds are expected to spread northward 
across northeastern Florida, Georgia, and the Carolina coasts 
through Friday.  Hurricane conditions are possible through 
Friday along the coasts of northeastern Florida, Georgia and South 
Carolina where a Hurricane Watch in effect. 

3. Widespread, life-threatening catastrophic flooding, with major to 
record river flooding, will continue today across portions of 
central Florida with considerable flooding in northern Florida, 
southeastern Georgia and eastern South Carolina expected today 
through the end of the week.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 28.0N  80.9W   55 KT  65 MPH...INLAND
 12H  29/1800Z 28.9N  80.4W   55 KT  65 MPH...OVER WATER
 24H  30/0600Z 30.2N  80.0W   55 KT  65 MPH...OVER WATER
 36H  30/1800Z 32.2N  80.1W   60 KT  70 MPH...OVER WATER
 48H  01/0600Z 34.3N  80.8W   35 KT  40 MPH...INLAND
 60H  01/1800Z 35.8N  81.7W   25 KT  30 MPH...INLAND
 72H  02/0600Z...DISSIPATED

$$
Forecaster Berg



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