Central Pacific Basin Tropical Cyclones

Tropical Storm Calvin Forecast Discussion

WTPA41 PHFO 171458

Tropical Storm Calvin Discussion Number  24
NWS Central Pacific Hurricane Center Honolulu HI   EP032023
500 AM HST Mon Jul 17 2023

Conventional infrared satellite imagery shows that Tropical 
Storm Calvin's low-level circulation center (LLCC) appears to be 
partially exposed early this morning. Therefore, the system has  
crossed longitude 140W into the Central Pacific Hurricane Center 
(CPHC's) area of responsibility. Scatterometer passes from last 
evening showed a large swath of winds of 40-45 kt north of the 
LLCC. The subjective Dvorak satellite classification from PHFO is
55 kt, SAB and JTWC are 35 kt, and TAFB's final fix is 45 kt. Based 
on these observations, we are maintaining the current intensity at 
45 kt for this advisory.

Calvin continues to move over cool SSTs of around 24 degrees C, and 
in a dry and stable environment. In the next 18-24 hours, the SSTs 
are expected to start gradually increasing as the cyclone begins to 
move closer to the main Hawaiian Islands. Southerly vertical wind 
shear will likely increase as Calvin nears the Big Island of 
Hawaii. This shear combined with entertainment of drier air into 
the system is expected to cause Calvin to weaken. This scenario 
would likely result in most of the deep convection (assuming it 
redevelops in the next day or two) being displaced to the north of 
the LLCC. The intensity forecast lies near the model consensus, 
and is similar to the previous official forecast we inherited from 
the National Hurricane Center (NHC) in Miami, Florida. Note that 
based on the recent scatterometer passes, we have expanded the 
wind radii in the northern semicircle.

The mid-level ridge to the north of Calvin will likely maintain a 
relatively rapid westward motion during the next few days. On this 
track, Calvin will likely move near or over the Big Island of 
Hawaii Tuesday night and Wednesday. It should then continue moving 
westward until it dissipates. The official forecast is near the 
previous NHC forecast, and lies close to the model consensus 


1. Calvin is forecast to pass very close to the Big Island Tuesday 
night and Wednesday, 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.


INIT  17/1500Z 16.8N 141.4W   45 KT  50 MPH
 12H  18/0000Z 17.1N 144.1W   40 KT  45 MPH
 24H  18/1200Z 17.4N 147.7W   40 KT  45 MPH
 36H  19/0000Z 17.8N 151.4W   40 KT  45 MPH
 48H  19/1200Z 18.4N 155.1W   35 KT  40 MPH
 60H  20/0000Z 19.0N 158.5W   30 KT  35 MPH
 72H  20/1200Z 19.7N 162.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  21/1200Z...DISSIPATED

Forecaster Houston

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