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Tropical Storm Calvin Discussion Number  23
NWS National Hurricane Center Miami FL       EP032023
1100 PM HST Sun Jul 16 2023
 

Calvin continues to slowly weaken this evening, with warming cloud 
tops and an asymmetric convective pattern, mainly on the eastern 
portion of the system. Satellite imagery depicts that banding 
features have also become less defined. Based on a blend of 
subjective Dvorak estimates from SAB and TAFB, as well as ADT and 
AiDT values from CIMMS, the intensity is lowered to 45 kt for this 
advisory.

Calvin is currently moving over cool SSTs of around 24 degrees C, 
and in a dry and stable environment. In about 24 hours, the ocean 
temperatures will slightly increase as the system approaches Hawaii, 
and many models suggest that Calvin will still be producing winds 
near tropical-storm-force when it nears the Hawaiian Islands. As the 
cyclone reaches the Hawaiian Islands, southerly vertical wind shear 
will increase and GFS and ECMWF simulated satellite images show most 
of the convection displaced on the northern side of the semi-circle. 
The increased vertical wind shear and drier air will cause Calvin to 
weaken after it passes the island chain and to dissipate by 96 
hours. The intensity forecast lies near the model consensus and is 
similar to the previous official NHC forecast.
 
A mid-level ridge to the north of Calvin should maintain a generally 
westward motion for the next few days.  On this track, Calvin will 
be entering the central Pacific basin early tomorrow morning, and 
move near or over the Big Island of Hawaii early Wednesday.  It 
should then continue westward until it dissipates. The official 
forecast is near the previous NHC forecast and lies close to the 
model consensus guidance.

This is the last forecast/advisory issued by the National Hurricane 
Center on Calvin. Future information on this system can be found 
in the forecast/advisories issued by the Central Pacific Hurricane 
Center beginning at 1500 UTC. 
 
KEY MESSAGES:
 
1. Calvin is forecast to approach the Hawaiian Islands during the 
next couple of days, bringing the potential for heavy rainfall and 
dangerous surf and rip currents. A Tropical Storm Watch could be 
issued for portions of the main Hawaiian Islands on Monday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0900Z 16.7N 139.7W   45 KT  50 MPH
 12H  17/1800Z 17.1N 142.3W   40 KT  45 MPH
 24H  18/0600Z 17.4N 145.9W   40 KT  45 MPH
 36H  18/1800Z 17.7N 149.6W   40 KT  45 MPH
 48H  19/0600Z 18.2N 153.4W   35 KT  40 MPH
 60H  19/1800Z 18.8N 156.9W   30 KT  35 MPH
 72H  20/0600Z 19.5N 160.3W   25 KT  30 MPH
 96H  21/0600Z...DISSIPATED
 
$$
Forecaster Kelly/Cangialosi
 
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