Post-Tropical Cyclone Idalia Discussion Number  22
NWS National Hurricane Center Miami FL       AL102023
1100 PM EDT Thu Aug 31 2023

Satellite images indicate that Idalia continues to exhibit the 
appearance of an extratropical cyclone with a frontal boundary 
extending from the center northeastward.  There is almost no deep 
convection associated with the system, but there continues to be 
areas of heavy rain along the front extending to near the coast of 
North Carolina.  The initial intensity remains 55 kt.

The cyclone is moving eastward at about 20 kt.  A slightly slower 
motion to the east-southeast is expected during the next day or two 
as the system continues to move near the base of a mid- to 
upper-level trough.  However, the steering currents are expected to 
weaken over the weekend as the storm approaches Bermuda, which 
should cause a significant slow down.  A turn to the northeast is 
forecast late in the weekend when another shortwave trough 
approaches the system.  The guidance is slower this cycle, and the 
NHC track forecast has been adjusted accordingly.

Gradual weakening is expected through early Saturday as the system 
separates from the mid- to upper-level trough.  However, as Idalia 
transitions back to a tropical cyclone near Bermuda, slow 
strengthening seems likely.  Based on the GFS and ECMWF models, 
Idalia will likely transition back to an extratropical cyclone in 
about 5 days.  The intensity forecast is similar to the previous 
one and fairly close to the GFS model.


KEY MESSAGES:

1. Tropical storm conditions are possible in Bermuda by Saturday.
Heavy rainfall will likely lead to areas of flash and urban
flooding on the island.

2. Water levels are expected to subside and winds are expected to
diminish along the coast of North Carolina through early Friday.


FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 33.1N  71.5W   55 KT  65 MPH...POST-TROPICAL
12H  01/1200Z 32.3N  69.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
24H  02/0000Z 31.1N  67.2W   45 KT  50 MPH...POST-TROP/EXTRATROP
36H  02/1200Z 30.6N  65.9W   40 KT  45 MPH...POST-TROP/EXTRATROP
48H  03/0000Z 31.3N  64.5W   40 KT  45 MPH...TROPICAL CYCLONE
60H  03/1200Z 32.3N  63.0W   45 KT  50 MPH
72H  04/0000Z 34.3N  61.0W   50 KT  60 MPH
96H  05/0000Z 36.8N  59.0W   50 KT  60 MPH
120H  06/0000Z 38.7N  61.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi