Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 150853

Tropical Storm Greg Discussion Number   6
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
1100 PM HST Mon Aug 14 2023

Deep convection associated with Greg continues to develop over and 
west of the low-level circulation this evening, due to a slight 
increase in easterly shear in the past few hours that was estimated 
to be around 5 to 10 kt. Recent SSMIS (0359Z) microwave data, 
however, showed some evidence of a formative inner core beginning 
to evolve. The various 06 UTC objective and subjective satellite 
intensity estimates ranged from 35-45 kt. As a result, the initial 
intensity is raised to 45 kt.     

The initial motion for this advisory is 270/12 kt, as Greg 
continues to move south of the subtropical ridge. Greg is forecast 
to gradually turn west-northwestward over the next couple of days 
while being steered by a mid- to upper-level ridge to the north. 
Thereafter, a gradual turn to the west-southwest is forecast as the 
weakening system becomes steered by the low- to mid-level flow. 
This forecast track is slightly south of the previous track through 
day 2, with very little differences thereafter as Greg passes well 
south of the Hawaiian Islands. This forecast track closely follows 
a combination of the previous forecast, HCCA, and TVCE. 

The tropical storm has a brief window to intensify over the next 24 
to 36 h as it tracks over warm SSTs (27-28C) and remains in a 
relatively moist environment with minimal shear. Therefore, the 
forecast depicts some strengthening within the initial 24 h, then 
remains steady through 36 h, which is supported by the latest 
intensity consensus aids. Beyond that, drier mid-level air along 
with an increase in shear and slightly cooler waters should result 
in a weakening trend, with Greg becoming post-tropical by day 4.


INIT  15/0900Z 11.2N 144.6W   45 KT  50 MPH
 12H  15/1800Z 11.3N 146.3W   50 KT  60 MPH
 24H  16/0600Z 11.7N 148.7W   50 KT  60 MPH
 36H  16/1800Z 12.2N 151.2W   50 KT  60 MPH
 48H  17/0600Z 12.6N 153.6W   45 KT  50 MPH
 60H  17/1800Z 12.6N 156.0W   45 KT  50 MPH
 72H  18/0600Z 12.3N 158.5W   40 KT  45 MPH
 96H  19/0600Z 11.5N 163.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  20/0600Z...DISSIPATED

Forecaster Gibbs/Jelsema

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