Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 171448

Tropical Storm Greg Discussion Number  15
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
500 AM HST Thu Aug 17 2023

Greg has quickly become disorganized overnight, with convection
becoming further displaced to the north, and then rapidly weakening.
As the convection became displaced, the exposed low level center 
began moving south of due west. The subjective and objective 
estimates range from 25 to 45 kt. A blend of these lead to 
lowering the initial intensity to 35 kt, but that may be too 
generous. It is possible that Greg could be declared post-tropical 
later today.

The initial motion is 270/11 kt. As the convection weakened, the 
exposed low level center took a short jog to the west-southwest, 
but is now back on its expected westward path. This westward motion 
is expected to continue today as Greg follows the southern edge of 
a ridge to the north. This path will have Greg passing well south 
of Hawaii today, before turning to the west-southwest as it 
weakens. The forecast track closely follows the previous package 
leaning towards the TVCA which remains in the middle of the 
relatively tightly clustered guidance. 

The intensity forecast is a bit more challenging. Limited convection
has become significantly sheared to the north of the low level 
center. Statistical guidance shows Greg remaining in a low sheared
environment for the next 24 hours. However the satellite depiction 
would suggest that Greg was under the influence of stronger shear
overnight. While it is possible for convection to redevelop near 
the center should shear remain low, there is good agreement in the 
guidance that shear will increase from the west to northwest 
beyond 24 hours. This leaves a limited window for any development 
of the system. Have held the intensity at 35 kt for the first 12 
hours, and then followed the gradual weakening trend of the 
dynamical guidance.


INIT  17/1500Z 11.9N 155.6W   35 KT  40 MPH
 12H  18/0000Z 12.0N 157.4W   35 KT  40 MPH
 24H  18/1200Z 11.9N 159.9W   30 KT  35 MPH
 36H  19/0000Z 11.5N 162.5W   30 KT  35 MPH
 48H  19/1200Z 11.1N 165.1W   30 KT  35 MPH...POST-TROP/REMNT LOW
 60H  20/0000Z 10.6N 167.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  20/1200Z...DISSIPATED

Forecaster M Ballard

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