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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
advisory.
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.
FORECAST POSITIONS AND MAX WINDS
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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