Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 170241

Tropical Storm Greg Discussion Number  13
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
500 PM HST Wed Aug 16 2023

Deep convection surrounding Greg continues to pulse under the 
influence of southeasterly vertical wind shear. This has displaced 
much of the convection to the north of a partially exposed 
low-level circulation center. Dvorak current intensity estimates 
range from 2.0/30 kt by SAB, to 3.5/35 kt out of JTWC, to 3.0/45 kt 
at HFO. Since a 2343 UTC CIMSS SATCON came in at 43 kt and CIMSS ADT 
was recently holding as high as 37 kt, a blend of the inputs 
supports keeping the official intensity at 40 kt for this advisory, 
though that may be generous.

Greg remains on a relatively steady forward motion that is slightly 
north of due west, 280/11 kt. A low- to mid-level ridge far to the 
north will keep the tropical cyclone moving along a general 
westward track through Thursday night, 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 altered little 
from the prior advisory and lies near TVCE in the middle of a 
tightly clustered guidance envelope.

Relatively light, southerly vertical wind shear will likely produce 
only slow weakening of Greg over the next day or so. Beyond 24 
hours, the dynamical guidance suggests steady weakening, likely due 
to a gradual increase in northerly vertical wind shear produced by 
a strengthening ridge aloft to the north. Conversely, the 
statistical guidance shows little short term change in Greg, 
followed by some strengthening. Given the tropical cyclone's 
inability to strengthen within the current shear environment and 
sufficiently warm SST, the official forecast follows the steady 
weakening trend of the dynamical guidance beyond 24 hours, and Greg 
is expected to become a post-tropical remnant low by late Friday or 


INIT  17/0300Z 12.1N 153.5W   40 KT  45 MPH
 12H  17/1200Z 12.2N 155.2W   40 KT  45 MPH
 24H  18/0000Z 12.3N 157.6W   35 KT  40 MPH
 36H  18/1200Z 12.1N 160.3W   35 KT  40 MPH
 48H  19/0000Z 11.7N 163.0W   30 KT  35 MPH
 60H  19/1200Z 11.3N 165.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  20/0000Z 10.8N 168.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  21/0000Z...DISSIPATED

Forecaster Wroe

Source link