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Hurricane Calvin Discussion Number  17
NWS National Hurricane Center Miami FL       EP032023
1100 AM HST Sat Jul 15 2023
 
The satellite appearance of Calvin has shown some ill effects today 
from cooler SSTs and some drier air in its surrounding environment. 
A 1512 UTC SSMIS 89 GHz passive microwave image of the hurricane 
showed the eyewall was open to the east, where a dry slot was noted 
earlier wrapping around that portion of the circulation. Since then, 
the eye has become a bit warmer and more pronounced in infrared 
satellite imagery, and some deeper inner-core convection has wrapped 
around the center. The latest objective and subjective satellite 
intensity estimates range from 77-90 kt. Based on a blend of these 
data and recent satellite trends, the initial intensity is held at 
85 kt for this advisory. 

Weakening is expected during the next few days as the cyclone moves 
into a drier and more stable air mass over sub-26C SSTs. In fact, 
model-simulated satellite imagery from the GFS and ECMWF suggest 
Calvin could lose most, or briefly all, of its convection once it 
enters the central Pacific basin. However, the underlying SSTs 
become slightly warmer between 48-96 h while the deep-layer shear 
diagnosed by the global models is low to moderate. Therefore, it 
seems that Calvin could regenerate new bursts of convection on its 
approach to Hawaii, which is shown by the global and hurricane 
models. Therefore, the NHC forecast keeps Calvin a tropical cyclone 
through 96 h. Regardless of its status, the cyclone appears likely 
to maintain some tropical-storm-force winds in the northern portion 
of its circulation as it approaches Hawaii. The global model fields 
suggest the system will be close to opening into a trough by or 
shortly after day 5.

The long-term motion of Calvin is westward at 280/14 kt. A westward 
to west-northwestward motion will continue through the forecast 
period as the cyclone is steered by a mid-level ridge entrenched 
over the eastern Pacific. Calvin is forecast to cross 140W and enter 
the central Pacific basin on Monday morning and approach the 
Hawaiian Islands on Tuesday into early Wednesday. The various track 
models continue to bring Calvin near or over the Big Island of 
Hawaii, but exactly where it will track relative to the island is 
still unclear given the cross-track spread noted at day 3 and 
beyond. The updated NHC forecast has been adjusted slightly faster 
than the previous one, but otherwise very little change was made.
 
 
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  15/2100Z 15.0N 130.4W   85 KT 100 MPH
 12H  16/0600Z 15.6N 132.7W   75 KT  85 MPH
 24H  16/1800Z 16.3N 135.8W   65 KT  75 MPH
 36H  17/0600Z 16.8N 139.0W   55 KT  65 MPH
 48H  17/1800Z 17.3N 142.5W   50 KT  60 MPH
 60H  18/0600Z 17.7N 146.2W   45 KT  50 MPH
 72H  18/1800Z 18.3N 149.9W   40 KT  45 MPH
 96H  19/1800Z 19.4N 156.8W   35 KT  40 MPH
120H  20/1800Z 20.5N 164.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Reinhart
 
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