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Hurricane Calvin Discussion Number  18
NWS National Hurricane Center Miami FL       EP032023
500 PM HST Sat Jul 15 2023

During the past several hours, the satellite cloud pattern of 
Calvin has been unsteady, with the eye coming and going and the 
eyewall cloud top temperatures fluctuating.  Overall, though, there 
has been little change in the organization and the various 
satellite intensity estimates.  Based on this, the initial 
intensity is again held at 85 kt, which is close to the CIMMS 
satellite consensus estimate.

Calvin is currently over 25C sea surface temperatures, and it should 
be over 24C water in about 24 h.  This should cause weakening during 
the next 24-36 h.  After that time, the sea surface temperatures 
start to increase under the forecast track, although they are 
expected to stay below 26C until the system passes near Hawaii.  
During this period, the vertical wind shear is forecast to be light 
to moderate.  The consensus of the guidance during this time is 
that Calvin will continue to weaken while producing intermittent 
bursts of convection, and that is the basis for keeping it a 
tropical storm.  Regardless of how much convection is present, it 
appears likely that Calvin will maintain tropical-storm-force winds 
as it passes near the Big Island of Hawaii.  After 96 h, stronger 
shear should cause the cyclone to degenerate to a remnant low 
pressure area or trough.

The initial motion is now 285/15 kt.  As in the previous forecast, 
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. On the forecast track, 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.  There remains some cross-track spread in the 
models, so while the new forecast track calls for Calvin to pass 
close to the Big Island of Hawaii it remains unclear exactly how it 
will track relative to the island.  The new forecast track has only 
minor adjustments from the previous track.
 
 
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  16/0300Z 15.4N 132.0W   85 KT 100 MPH
 12H  16/1200Z 16.0N 134.3W   75 KT  85 MPH
 24H  17/0000Z 16.6N 137.6W   65 KT  75 MPH
 36H  17/1200Z 17.1N 140.9W   55 KT  65 MPH
 48H  18/0000Z 17.4N 144.4W   50 KT  60 MPH
 60H  18/1200Z 17.9N 148.0W   45 KT  50 MPH
 72H  19/0000Z 18.4N 151.6W   40 KT  45 MPH
 96H  20/0000Z 19.5N 158.5W   35 KT  40 MPH
120H  21/0000Z 20.5N 165.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Beven
 
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