Central Pacific Basin Tropical Cyclones

Tropical Storm Calvin Forecast Discussion

WTPA41 PHFO 180245

Tropical Storm Calvin Discussion Number  26
NWS Central Pacific Hurricane Center Honolulu HI   EP032023
500 PM HST Mon Jul 17 2023

Satellite data showed an exposed low-level circulation all day.
Although most of the deep convection today remained in the outer 
circulation in the northern semicircle, recent images showed 
some deep convection developing closer to the center. A US Air Force 
Reserve WC-130J completed its recon mission this morning. The next 
mission will be flown to support tonight's forecast packages. 
Subjective Dvorak intensity estimates came in at 35 kt for PHFO and 
JTWC. The latest CIMSS SATCON showed 43 kt. The initial intensity 
for this advisory is 40 kt based on a blend of these estimates.

The initial motion for this advisory is 275/19 kt as Calvin moves
quickly westward to the south of a subtropical ridge. This speed is
a slight increase from the previous package. This steering is
expected to continue over the next several days. The dynamical
guidance indicates that the center of Calvin will pass over or just
south of the Big Island on Tuesday night. The track forecast is 
close to the previous forecast, but is a bit faster. It is also 
close to the HCCA guidance.

The surrounding environment around Calvin continues to be dry and
stable with SSTs around 24-25C. As Calvin moves westward, the SSTs
will gradually increase, with values of 26-27C around the main
Hawaiian Islands. The higher SSTs may result in deep convection
becoming better developed, which is suggested by model-simulated
satellite imagery from some of the dynamical models. This is should
keep Calvin at tropical storm intensity by the time it reaches the
Big Island. As a result, Hawaii County has been put in a Tropical
Storm Warning starting with this advisory. Calvin will also be
affected by an upper tropospheric trough in about 36-48 hrs. The
trough will increase the vertical shear over the tropical cyclone
and result post-tropical/remnant low status Wednesday night or more 
likely Thursday.


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

2. It is important to not focus on the exact forecast track and
intensity when preparing for Calvin. Persons in Hawaii County
should prepare now through Tuesday for impacts prior to the onset of
tropical storm force winds. These impacts could include flash
flooding, damaging winds, and large and dangerous surf.


INIT  18/0300Z 17.4N 145.4W   40 KT  45 MPH
 12H  18/1200Z 17.7N 148.4W   40 KT  45 MPH
 24H  19/0000Z 18.3N 152.3W   40 KT  45 MPH
 36H  19/1200Z 18.9N 156.0W   35 KT  40 MPH
 48H  20/0000Z 19.5N 159.8W   30 KT  35 MPH
 60H  20/1200Z 19.9N 163.5W   25 KT  30 MPH
 72H  21/0000Z 20.0N 167.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  22/0000Z...DISSIPATED

Forecaster Kodama

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