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Tropical Storm Calvin Discussion Number  20...Corrected
NWS National Hurricane Center Miami FL       EP032023
500 AM HST Sun Jul 16 2023

Corrected timing in the key messages
 
The cloud pattern of Calvin has further deteriorated this morning. 
The center is now exposed, and cloud tops have warmed over much of 
the circulation with only a small area of moderate to deep 
convection noted to the east of the center. The objective and 
subjective satellite intensity estimates continue to quickly 
decline, with a blend of the recent data suggesting that Calvin is 
no longer a hurricane. Based on these data and its poor satellite 
structure, the initial intensity is lowered to 60 kt.

The track forecast remains straightforward. Calvin is expected to 
keep moving generally westward for the next several days as it is 
steered by a well-established ridge over the eastern Pacific. This 
motion will bring the cyclone into the central Pacific basin (west 
of 140W) tonight or early Monday morning. Calvin is forecast to 
approach the Hawaiian Islands on Tuesday and pass near or over the 
Big Island of Hawaii early Wednesday. The track guidance remains in 
good agreement on this overall scenario, although the details of its 
track near Hawaii are still uncertain given the average amount of 
cross-track spread in the guidance. The latest NHC forecast is 
slightly faster and has been nudged slightly northward at 60-96 h, 
but still lies near the center of the guidance envelope and close to 
the HCCA and TVCE aids.   

Calvin will move over 24 deg C waters and into a drier, more stable 
environment during the next couple of days. Therefore, continued 
weakening is anticipated, and the system could struggle to produce 
convection on its trek into the central Pacific basin. As Calvin 
moves closer to Hawaii, model-simulated satellite imagery suggests 
it could produce some renewed bursts of convection to the north of 
its center. This forecast keeps Calvin as a tropical cyclone through 
72 h, although it could become post-tropical sooner if convection 
collapses for an extended period. Regardless, there is good support 
from both the global and hurricane models that Calvin will maintain 
some tropical-storm-force winds (mainly to the north of its center) 
as it nears Hawaii. With strong deep-layer southwesterly shear 
expected in 96-120 h, this forecast shows Calvin opening into a 
trough and dissipating by day 5.
 
 
KEY MESSAGES:
 
1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands during the next few days. A Tropical 
Storm Watch could be issued for portions of the main Hawaiian 
Islands later today, and interests in Hawaii should closely monitor 
the latest forecast updates.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/1500Z 16.0N 134.8W   60 KT  70 MPH
 12H  17/0000Z 16.4N 137.3W   55 KT  65 MPH
 24H  17/1200Z 17.0N 140.6W   45 KT  50 MPH
 36H  18/0000Z 17.5N 144.2W   45 KT  50 MPH
 48H  18/1200Z 17.9N 147.9W   40 KT  45 MPH
 60H  19/0000Z 18.6N 151.6W   40 KT  45 MPH
 72H  19/1200Z 19.2N 155.0W   35 KT  40 MPH
 96H  20/1200Z 20.1N 161.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  21/1200Z...DISSIPATED
 
$$
Forecaster Reinhart
 
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