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Tropical Storm Calvin Discussion Number  21
NWS National Hurricane Center Miami FL       EP032023
1100 AM HST Sun Jul 16 2023
 
The satellite presentation of Calvin has not changed much since the 
last advisory. Satellite images show a partially exposed low-level 
circulation with a small area of moderate to deep convection near 
the center. Satellite intensity estimates continue to fall, and a 
blend of the latest Dvorak final-T and current intensity estimates 
from TAFB and SAB support lowering the intensity to 55 kt. 

Continued weakening is expected as Calvin moves over 24C SSTs and 
into a drier, more stable environment during the next couple of 
days. The cyclone could cease producing organized convection during 
this time. Although environmental and oceanic conditions remain 
marginal on its approach to Hawaii, there is still support in GFS, 
ECMWF, and HAFS model-simulated satellite imagery for some new 
bursts of convection as Calvin moves closer to the islands. So, the 
NHC forecast keeps Calvin a tropical cyclone through 72 h, although 
post-tropical status could occur sooner than forecast. Regardless, 
the cyclone should still be producing some tropical-storm-force 
winds in its northern semicircle upon its closest approach to 
Hawaii, especially given the storm's fast forward motion. 

There has been no change to the track forecast reasoning. A 
mid-level ridge over the eastern Pacific is expected to steer Calvin 
generally westward into the central Pacific basin late tonight or 
early Monday and toward the Hawaiian Islands on Tuesday. The NHC 
forecast shows the center of Calvin passing near or over the Big 
Island of Hawaii early Wednesday, then continuing westward and 
becoming post-tropical on Thursday before dissipating. The guidance 
envelope has trended slightly southward this cycle, but little 
change was required to the NHC forecast as it still lies near the 
latest HFIP corrected consensus approach (HCCA) aid.

While the exact storm track near Hawaii is still uncertain, there is 
potential for portions of the state to experience some heavy 
rainfall, dangerous surf and rip current conditions, and minor wind 
impacts from Calvin. A Tropical Storm Watch may be required for 
portions of the main Hawaiian Islands later today.
 
 
KEY MESSAGES:
 
1. Calvin is forecast to approach the Hawaiian Islands during the 
next couple of days or so, bringing the potential for heavy 
rainfall and dangerous surf and rip current conditions. A Tropical 
Storm Watch could be issued for portions of the main Hawaiian 
Islands later today.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/2100Z 16.1N 136.3W   55 KT  65 MPH
 12H  17/0600Z 16.5N 138.8W   45 KT  50 MPH
 24H  17/1800Z 17.1N 142.3W   40 KT  45 MPH
 36H  18/0600Z 17.5N 145.9W   40 KT  45 MPH
 48H  18/1800Z 18.1N 149.7W   35 KT  40 MPH
 60H  19/0600Z 18.7N 153.4W   35 KT  40 MPH
 72H  19/1800Z 19.2N 157.0W   35 KT  40 MPH
 96H  20/1800Z 20.0N 163.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  21/1800Z...DISSIPATED
 
$$
Forecaster Reinhart
 
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