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Tropical Storm Idalia Forecast Discussion



000
WTNT45 KNHC 272059
TCDAT5

Tropical Storm Idalia Discussion Number   5
NWS National Hurricane Center Miami FL       AL102023
400 PM CDT Sun Aug 27 2023

Idalia's cloud pattern is gradually becoming a little better
organized, with a curved convective band forming over the southern
semicircle of the circulation.  Upper-level outflow is currently
restricted over the northern portion of the system, however.
The advisory intensity is held at 35 kt based on a subjective
Dvorak estimate from TAFB.  Another aircraft reconnaissance mission
into the storm is scheduled for tonight.

The tropical cyclone continues to move rather slowly, and the
initial motion estimate is 040/3 kt. Idalia should remain in a weak
steering pattern through tonight so slow and possibly erratic
motion is likely for the next 12 hours.  On Monday, a mid-level
ridge begins to build to the northeast of the tropical cyclone.
This should result in a slightly east of northward motion during
the next day or two.  When the system moves into the northeast Gulf
of Mexico, a mid-level trough developing over the eastern United
states will likely cause Idalia to turn northeastward with an
increase in forward speed.  The new official forecast is again
shifted slightly eastward, and is somewhat faster than the previous
one.  This is a blend of the latest ECMWF and GFS solutions and is
also between the simple and corrected dynamical consensus tracks.

The intensity forecast is somewhat challenging.  Idalia will be 
traversing eastern Gulf of Mexico waters of high oceanic heat 
content, and the environmental air mass should remain fairly moist.  
The flow to the east of an upper-level trough could impart some 
vertical wind shear over the system, but this shear could also be 
compensated by the conducive effect of upper-level diffluence.  
There is considerable spread in the model intensity guidance, 
ranging from minimal to major hurricane status before landfall on 
the northeast Gulf coast.  The official intensity forecast is a 
little higher than the previous one, and remains near the higher 
end of the guidance.  Given the uncertainties, users should monitor 
future NHC forecasts for possible changes in the predicted strength 
of Idalia, and prepare for possible significant impacts within the 
hurricane and storm surge watch areas.


KEY MESSAGES:

1. Idalia is forecast to become a hurricane over the eastern Gulf of 
Mexico, and there is an increasing risk of life-threatening storm 
surge and hurricane-force winds along portions of the west coast of 
Florida and the Florida Panhandle beginning as early as Tuesday.  
Although it is too soon to specify the exact location and magnitude 
of these impacts, residents in these areas should monitor updates to 
the forecast and follow any advice given by local officials.  Storm 
surge and hurricane watches have been issued for portions of the 
west coast of Florida and the coast of the Florida Panhandle, and 
residents in these areas should monitor updates to the forecast and 
follow any advice given by local officials.

2. Scattered flash and urban flooding can be expected across 
portions of the west coast of Florida, the Florida Panhandle and 
portions of the Southeast U.S. by Tuesday into Thursday.  Flooding 
from heavy rainfall is likely over portions of the southeast U.S. by 
mid to late week. 

3. Heavy rainfall from Tropical Storm Idalia is expected across 
portions of the eastern Yucatan and western Cuba and may produce 
areas of flash and urban flooding as well as landslides across 
western Cuba. 

4. Tropical storm conditions are expected over portions of the 
Yucatan Peninsula and extreme western Cuba with tropical storm 
conditions possible on the Isle of Youth. 


FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 20.1N  85.5W   35 KT  40 MPH
 12H  28/0600Z 20.5N  85.3W   45 KT  50 MPH
 24H  28/1800Z 21.7N  85.0W   55 KT  65 MPH
 36H  29/0600Z 23.4N  84.9W   65 KT  75 MPH
 48H  29/1800Z 25.6N  84.5W   75 KT  85 MPH
 60H  30/0600Z 28.7N  83.7W   85 KT 100 MPH
 72H  30/1800Z 31.3N  81.9W   50 KT  60 MPH...INLAND
 96H  31/1800Z 34.5N  76.0W   50 KT  60 MPH...OVER WATER
120H  01/1800Z 35.0N  71.0W   55 KT  65 MPH

$$
Forecaster Pasch



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