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Tropical Storm Greg Discussion Number 7
NWS Central Pacific Hurricane Center Honolulu HI EP082023
500 AM HST Tue Aug 15 2023
Deep convection has increased over the center of the system during
the past few hours, which is a result of the persistent east-
southeasterly shear over the past 12 to 18 h easing. Recent
microwave data from AMSR2 (1137 UTC) showed evidence of an inner
core that has developed, which has improved from previous microwave
data. Based on the microwave data and the 12 UTC subjective Dvorak
intensity estimates ranging from 35 to 45 kt between PHFO, SAB, AND
JTWC, the initial intensity is held at 45 kt.
The initial motion for this advisory remains at 270/12 kt, as Greg
continues to move south of the subtropical ridge. Greg is forecast
to gradually turn west-northwestward through the day today while
being steered by a mid- to upper-level ridge to the north, which
will persist through late Wednesday. Thereafter, a gradual turn to
the west-southwest is forecast as the weakening system becomes
steered by the low- to mid-level flow. This forecast track is very
similar to the previous forecast, and shows Greg passing well south
of the Hawaiian Islands Wednesday night through Thursday night.
This forecast track closely follows a combination of the previous
forecast, HCCA, and TVCE.
The tropical storm has a brief window to intensify over the next 36
h as it tracks over warm SSTs (27-28C) and remains in a relatively
moist environment with minimal shear. Therefore, the forecast
depicts some strengthening within the initial 36 h, which is
supported by the latest intensity consensus aids. Beyond that,
drier mid-level air along with the potential for a slight increase
in shear and cooler waters should result in a weakening trend, with
Greg becoming post-tropical on day 4.
FORECAST POSITIONS AND MAX WINDS
INIT 15/1500Z 11.1N 145.9W 45 KT 50 MPH
12H 16/0000Z 11.4N 147.6W 50 KT 60 MPH
24H 16/1200Z 11.9N 150.1W 50 KT 60 MPH
36H 17/0000Z 12.4N 152.6W 55 KT 65 MPH
48H 17/1200Z 12.6N 155.0W 50 KT 60 MPH
60H 18/0000Z 12.4N 157.5W 45 KT 50 MPH
72H 18/1200Z 12.1N 160.2W 40 KT 45 MPH
96H 19/1200Z 11.3N 165.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 20/1200Z...DISSIPATED
$$
Forecaster Gibbs/Jelsema
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