Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 152047

Tropical Storm Greg Discussion Number   8
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
1100 AM HST Tue Aug 15 2023

The satellite presentation of Greg has not changed significantly 
this morning, as relatively light, easterly vertical wind shear 
continues to restrict outflow within the eastern semicircle. Deep 
convection has been persistent to the southwest of the low-level 
circulation center, while banding has developed to the north. HFO 
and JTWC reported a Dvorak current intensity of 3.0/45 kt, and 
CIMSS ADT came in at 41 kt. Given no substantial change in the 
satellite presentation, the current intensity will be held at 45 kt 
for this advisory.

The initial motion for this advisory is 275/12 kt. Greg is moving 
toward the west along the southern edge of a deep subtropical 
ridge. A turn toward the west-northwest is forecast later today and 
Wednesday as Greg advances toward a weakness in the ridge aloft. A 
turn toward the west is expected Thursday as the ridge aloft begins 
to strengthen, causing Greg to pass several hundred miles south of 
Hawaii. A turn toward the west-southwest is expected on Friday as 
the weakening tropical cyclone is steered by the deep ridge to the 
north. The forecast track was altered little from the prior 
advisory and lies near TVCE in the middle of a relatively clustered 
guidance envelope.

The greatest chance for strengthening lies within the next 24 hours 
or so, when vertical wind shear is expected to relax slightly and 
the SST remains around 28C. The statistical guidance has been 
tending to forecast intensification during this time and has been 
holding Greg at a higher intensity through the following several 
days. Meanwhile, the dynamical guidance is showing little to no 
intensification in the next 24 hours, followed by steady weakening, 
possibly due to drier air aloft disrupting the tropical cyclone and 
slightly cooler SST. The intensity forecast allows for 
intensification through Wednesday, followed by weakening from 
Thursday onward, with Greg becoming post-tropical on Saturday. This 
forecast follows the general trend of HCCA, though the official 
forecast is held slightly higher than this guidance through the 
next four days. 


INIT  15/2100Z 11.2N 147.2W   45 KT  50 MPH
 12H  16/0600Z 11.6N 149.0W   50 KT  60 MPH
 24H  16/1800Z 12.1N 151.5W   50 KT  60 MPH
 36H  17/0600Z 12.5N 153.9W   50 KT  60 MPH
 48H  17/1800Z 12.6N 156.4W   45 KT  50 MPH
 60H  18/0600Z 12.3N 159.0W   40 KT  45 MPH
 72H  18/1800Z 11.9N 161.7W   35 KT  40 MPH
 96H  19/1800Z 11.0N 166.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  20/1800Z...DISSIPATED

Forecaster Wroe

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