ZCZC MIATCDEP3 ALL
TTAA00 KNHC DDHHMM
 
Hurricane Calvin Discussion Number  16
NWS National Hurricane Center Miami FL       EP032023
500 AM HST Sat Jul 15 2023
 
The ragged eye of Calvin has been apparent at times in conventional 
satellite imagery this morning, but overall it has become less 
defined. Overnight GMI and more recent SSMIS passive microwave data 
show that some deep convection has eroded within the eastern portion 
of the eyewall. The vortex also appears somewhat tilted with height, 
as the 37 GHz low-level center was displaced a bit to the south of 
the 89 GHz mid-level one. A blend of the latest objective UW-CIMSS 
satellite estimates and subjective Dvorak classifications from TAFB 
and SAB support an initial intensity of 85 kt.    

The weakening trend that began last night is expected to continue 
for the next several days due to Calvin moving over cooler waters 
and into a drier and more stable environment. Also, southwesterly 
deep-layer shear is forecast to increase from 60-120 h as the 
cyclone traverses the central Pacific. This will adversely affect 
its ability to sustain organized convection, although to what extent 
is still somewhat uncertain. Regardless of its tropical or 
post-tropical status, Calvin appears likely to maintain some 
tropical-storm-force winds in the northern portion of its 
circulation through 96 h. Overall, few changes were made to the 
updated NHC intensity forecast, which closely follows the 
multi-model HCCA and IVCN aids. The global model fields suggest the 
system could open up into a trough soon after day 5.

Calvin is moving quickly west-northwestward at 285/14 kt. With a 
well-established mid-level ridge over the eastern Pacific, this 
general motion is expected to continue through the forecast period. 
This course brings Calvin into the central Pacific basin (west of 
140W) by Monday morning and toward the Hawaiian Islands on Tuesday 
and Wednesday. The guidance is reasonably well clustered on a track 
near or over the Big Island of Hawaii, but any potential impacts 
will be dictated by the track details that are still quite 
uncertain at this time. The updated NHC track forecast is a bit 
faster and slightly south of the previous one at days 3-5, in 
agreement with the latest consensus aids and near the center of the 
guidance envelope.
 
 
KEY MESSAGES:
 
1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands early next week. It is too early to
determine the exact location and magnitude of potential impacts
given uncertainties in the track, intensity, and structure of Calvin
as it approaches the islands. Interests in Hawaii should closely
monitor the latest forecast updates.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 14.7N 129.0W   85 KT 100 MPH
 12H  16/0000Z 15.3N 131.1W   80 KT  90 MPH
 24H  16/1200Z 16.0N 134.1W   70 KT  80 MPH
 36H  17/0000Z 16.6N 137.1W   60 KT  70 MPH
 48H  17/1200Z 17.1N 140.5W   55 KT  65 MPH
 60H  18/0000Z 17.6N 144.0W   50 KT  60 MPH
 72H  18/1200Z 18.1N 147.6W   45 KT  50 MPH
 96H  19/1200Z 19.1N 154.9W   35 KT  40 MPH
120H  20/1200Z 20.5N 161.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Reinhart
 
NNNN