Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 162041

Tropical Storm Greg Discussion Number  12
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
1100 AM HST Wed Aug 16 2023

Greg continues to be affected by southeasterly vertical wind shear, 
and pulsing deep convection remains largely displaced to the north 
and west of a partially exposed low-level circulation center. JTWC 
and SAB came in with a current intensity of 2.5/35 kt, and HFO 
estimated 3.5/55 kt, while CIMSS ADT was down at 37 kt. Given that 
the satellite presentation is slightly degraded, a blend of these 
inputs supports dropping the official intensity to 40 kt with this 

Greg remains on a relatively steady forward motion that is slightly 
north of due west, 280/12 kt. A low- to mid-level ridge far to the 
north will keep the tropical cyclone moving along a general 
westward track through the next 36 hours, causing Greg to pass well 
south of Hawaii. A turn toward the west-southwest is forecast on 
Friday as the weakening tropical cyclone is steered by a deepening 
ridge to the north. The official forecast track was changed little 
from the prior advisory and lies near TVCE in the middle of a 
tightly clustered guidance envelope.

The intensity forecast is more challenging. Relatively light, 
southerly vertical wind shear has been rather disruptive, leading 
to the pulsing deep convection near the center of Greg. Conditions 
will change little during the next 24 hours or so, and the official 
forecast indicates no change in intensity, which is higher than all 
guidance. Beyond 24 hours, guidance continues to split into two 
camps. The dynamical guidance shows steady weakening as a deep, 
strengthening ridge to the north imparts westerly to northwesterly 
vertical wind shear, while the statistical guidance continues to 
suggest some intensification. Given the tropical cyclone's 
inability to resist the current shear environment, the official 
forecast follows the steady weakening trend at the higher end of 
the dynamical guidance envelope beyond 24 hours, and Greg is 
expected to become a post-tropical remnant low this weekend.


INIT  16/2100Z 11.9N 152.5W   40 KT  45 MPH
 12H  17/0600Z 12.1N 154.3W   40 KT  45 MPH
 24H  17/1800Z 12.2N 156.6W   40 KT  45 MPH
 36H  18/0600Z 12.1N 159.1W   35 KT  40 MPH
 48H  18/1800Z 11.8N 161.7W   35 KT  40 MPH
 60H  19/0600Z 11.3N 164.4W   30 KT  35 MPH
 72H  19/1800Z 11.0N 167.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  20/1800Z 10.1N 171.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  21/1800Z...DISSIPATED

Forecaster Wroe

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