Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 151450

Tropical Storm Greg Discussion Number   7
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
500 AM HST Tue Aug 15 2023

Deep convection has increased over the center of the system during 
the past few hours, which is a result of the persistent east-
southeasterly shear over the past 12 to 18 h easing. Recent 
microwave data from AMSR2 (1137 UTC) showed evidence of an inner 
core that has developed, which has improved from previous microwave 
data. Based on the microwave data and the 12 UTC subjective Dvorak 
intensity estimates ranging from 35 to 45 kt between PHFO, SAB, AND 
JTWC, the initial intensity is held at 45 kt.

The initial motion for this advisory remains at 270/12 kt, as Greg 
continues to move south of the subtropical ridge. Greg is forecast 
to gradually turn west-northwestward through the day today while 
being steered by a mid- to upper-level ridge to the north, which 
will persist through late Wednesday. 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 very 
similar to the previous forecast, and shows Greg passing well south 
of the Hawaiian Islands Wednesday night through Thursday night. 
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 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 36 h, which is 
supported by the latest intensity consensus aids. Beyond that, 
drier mid-level air along with the potential for a slight increase 
in shear and cooler waters should result in a weakening trend, with 
Greg becoming post-tropical on day 4.


INIT  15/1500Z 11.1N 145.9W   45 KT  50 MPH
 12H  16/0000Z 11.4N 147.6W   50 KT  60 MPH
 24H  16/1200Z 11.9N 150.1W   50 KT  60 MPH
 36H  17/0000Z 12.4N 152.6W   55 KT  65 MPH
 48H  17/1200Z 12.6N 155.0W   50 KT  60 MPH
 60H  18/0000Z 12.4N 157.5W   45 KT  50 MPH
 72H  18/1200Z 12.1N 160.2W   40 KT  45 MPH
 96H  19/1200Z 11.3N 165.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  20/1200Z...DISSIPATED

Forecaster Gibbs/Jelsema

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