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Tropical Storm Greg Discussion Number 8
NWS Central Pacific Hurricane Center Honolulu HI EP082023
1100 AM HST Tue Aug 15 2023
The satellite presentation of Greg has not changed significantly
this morning, as relatively light, easterly vertical wind shear
continues to restrict outflow within the eastern semicircle. Deep
convection has been persistent to the southwest of the low-level
circulation center, while banding has developed to the north. HFO
and JTWC reported a Dvorak current intensity of 3.0/45 kt, and
CIMSS ADT came in at 41 kt. Given no substantial change in the
satellite presentation, the current intensity will be held at 45 kt
for this advisory.
The initial motion for this advisory is 275/12 kt. Greg is moving
toward the west along the southern edge of a deep subtropical
ridge. A turn toward the west-northwest is forecast later today and
Wednesday as Greg advances toward a weakness in the ridge aloft. A
turn toward the west is expected 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 expected on Friday as
the weakening tropical cyclone is steered by the deep ridge to the
north. The forecast track was altered little from the prior
advisory and lies near TVCE in the middle of a relatively clustered
guidance envelope.
The greatest chance for strengthening lies within the next 24 hours
or so, when vertical wind shear is expected to relax slightly and
the SST remains around 28C. The statistical guidance has been
tending to forecast intensification during this time and has been
holding Greg at a higher intensity through the following several
days. Meanwhile, the dynamical guidance is showing little to no
intensification in the next 24 hours, followed by steady weakening,
possibly due to drier air aloft disrupting the tropical cyclone and
slightly cooler SST. The intensity forecast allows for
intensification through Wednesday, followed by weakening from
Thursday onward, with Greg becoming post-tropical on Saturday. This
forecast follows the general trend of HCCA, though the official
forecast is held slightly higher than this guidance through the
next four days.
FORECAST POSITIONS AND MAX WINDS
INIT 15/2100Z 11.2N 147.2W 45 KT 50 MPH
12H 16/0600Z 11.6N 149.0W 50 KT 60 MPH
24H 16/1800Z 12.1N 151.5W 50 KT 60 MPH
36H 17/0600Z 12.5N 153.9W 50 KT 60 MPH
48H 17/1800Z 12.6N 156.4W 45 KT 50 MPH
60H 18/0600Z 12.3N 159.0W 40 KT 45 MPH
72H 18/1800Z 11.9N 161.7W 35 KT 40 MPH
96H 19/1800Z 11.0N 166.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 20/1800Z...DISSIPATED
$$
Forecaster Wroe
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