Central Pacific Basin Tropical Cyclones

Tropical Storm Greg Forecast Discussion

WTPA43 PHFO 160243

Tropical Storm Greg Discussion Number   9
NWS Central Pacific Hurricane Center Honolulu HI   EP082023
500 PM HST Tue Aug 15 2023

Deep convection around Tropical Storm Greg has been pulsing through 
the day, and a partially exposed low-level circulation center can 
be discerned through a thin veil of mid-level clouds on visible 
imagery this afternoon. Though light, southeasterly vertical wind 
shear is affecting the tropical storm, and fix agencies came in 
with a wide range of intensity estimates, from 2.5 out of SAB, to 
3.0 at HFO, and 3.5 from JTWC. The current intensity from CIMSS ADT 
was recently 47 kt, though that estimate was elevated due to deep 
convection that had flared late this morning. Given the lack of 
substantial improvement in the satellite presentation and pulsing 
nature of the deep convection, a blend of these inputs supports 
holding the intensity at 45 kt for this advisory.

The initial motion for this advisory is 280/12 kt. Greg appears to 
be starting the anticipated turn to the west-northwest toward a 
weakness aloft in the deep ridge north of the tropical cyclone. A 
general forward motion toward the west-northwest is expected 
tonight and much of Wednesday. Confidence is high that Greg will 
turn toward the west Wednesday night and 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 forecast 
Thursday night and Friday as the weakening tropical cyclone is 
steered by the deep ridge to the north. The official forecast track 
is essentially an update of the prior advisory and lies near TVCE 
in the middle of a relatively clustered guidance envelope.

The greatest chance for any additional strengthening will be in the 
short term, when vertical wind shear will remain light and the SST 
will hold around 28C. The guidance continues to be split into two 
camps. The statistical models are showing slight intensification 
over the next day or so followed by little change for several days. 
Conversely, the dynamical models show little to no short term 
intensification, followed by steady weakening through the next 
four days, possibly due to drier air aloft disrupting Greg and 
slightly cooler SST along the forecast track. The updated intensity 
forecast allows for some short term strengthening into Wednesday, 
followed by steady weakening as depicted by the bulk of the 
dynamical guidance, with Greg becoming post-tropical on Saturday.


INIT  16/0300Z 11.5N 148.3W   45 KT  50 MPH
 12H  16/1200Z 11.8N 150.2W   50 KT  60 MPH
 24H  17/0000Z 12.2N 152.6W   50 KT  60 MPH
 36H  17/1200Z 12.5N 155.1W   45 KT  50 MPH
 48H  18/0000Z 12.3N 157.6W   40 KT  45 MPH
 60H  18/1200Z 12.0N 160.2W   35 KT  40 MPH
 72H  19/0000Z 11.7N 162.9W   30 KT  35 MPH
 96H  20/0000Z 10.8N 168.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  21/0000Z...DISSIPATED

Forecaster Wroe

Source link