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Tropical Storm Calvin Discussion Number  27
NWS Central Pacific Hurricane Center Honolulu HI   EP032023
1100 PM HST Mon Jul 17 2023
 
The most recent conventional infrared satellite imagery continues 
to show the partially exposed low-level circulation center (LLCC) 
of Tropical Storm Calvin. Deep convection has been developing 
north of the LLCC during the past several hours. An aircraft 
from the 53rd Weather Reconnaissance Squadron "Hurricane Hunters" 
is currently sampling Tropical Storm Calvin  as it continues to 
move rapidly toward the Big Island of Hawaii late this evening. 
Their flight-level data support tropical storm force winds with 
this system. Recent satellite-based scatterometer passes also show 
winds of at least 35 kt over a broad swath north and northeast of 
the center. The most recent subjective Dvorak satellite intensity 
estimates were 35 kt from PHFO and JTWC. The current CIMSS SATCON 
estimate shows 41 kt. The initial intensity for this advisory is 
maintained at 40 kt based on a blend of these estimates.
 
Calvin's initial motion for this advisory is 275/19 kt as the 
cyclone continues to be steered rapidly westward south of a large 
subtropical ridge. This steering is expected to continue over the 
next 3 to 4 days. The dynamical guidance indicates that the center 
of Calvin will pass over, or just south of the Big Island Tuesday 
night. The latest track forecast is close to the previous 
forecast, which continues to closely follow the HCCA guidance.
 
The surrounding environment around Calvin continues to be 
relatively dry and stable. The SSTs are gradually increasing to 
around 25C, and we expect additional warming of the SSTs to 26-27C 
as it moves closer to the main Hawaiian Islands. The higher SSTs 
may support additional deep convection spreading around the 
northern semicircle of Calvin during the next day or two. This is 
expected to keep the cyclone at tropical storm intensity by the 
time it reaches the Big Island. As a result, a Tropical Storm 
Warning remains in effect for Hawaii County. After it passes 
southwest of the main Hawaiian Islands, we expect it to move near 
an upper tropospheric trough in about 36-48 hrs. This feature aloft 
will likely increase the vertical wind shear over the system, and 
will eventually result in it becoming a post-tropical/remnant low 
by Wednesday night or Thursday.
 
 
KEY MESSAGES:
 
1.  Calvin is forecast to pass over or very close to Hawaii County
Tuesday night, bringing a period of heavy rain, high surf and
locally strong winds. Calvin is expected to weaken as it moves
westward to the south of the other Hawaiian Islands Wednesday
and Wednesday night, bringing the potential for some peripheral
impacts.
 
2. It is important to not focus on the exact forecast track and
intensity when preparing for Calvin. Persons in Hawaii County
should prepare from now through Tuesday afternoon for impacts 
prior to the onset of tropical storm conditions. These impacts 
could include flash flooding, damaging winds, and large and 
dangerous surf.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0900Z 17.4N 147.5W   40 KT  45 MPH
 12H  18/1800Z 17.8N 150.4W   40 KT  45 MPH
 24H  19/0600Z 18.5N 154.2W   35 KT  40 MPH
 36H  19/1800Z 19.1N 158.0W   35 KT  40 MPH
 48H  20/0600Z 19.6N 161.7W   30 KT  35 MPH
 60H  20/1800Z 19.8N 165.3W   25 KT  30 MPH
 72H  21/0600Z 20.1N 169.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  22/0600Z...DISSIPATED
 
$$
Forecaster Houston
 
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