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Hurricane Calvin Discussion Number  15
NWS National Hurricane Center Miami FL       EP032023
1100 PM HST Fri Jul 14 2023
 
This evening's satellite and microwave presentation reveals a 
significantly degraded cloud pattern.  A recent SSMI/S image 
indicated inner core erosion in the southeast quadrant and no 
apparent outer ring development.  Calvin's eye has become obscured 
and has cooled (-27C), and the GFS model sounding indicated that 
there could be some southeasterly shear undercutting the upper-level 
diffluent flow.  The subjective intensity estimates from both TAFB 
and SAB yield 90 kt, the UW-CMISS objective ADT and AiDT intensity 
estimates are 87 and 88 kt, respectively. Additionally, a RADARSAT 
(RCM 2) SAR overpass estimated maximum sustained winds of 88-93 kt.  
Based on these data, the initial intensity is lowered to 90 kt for 
this advisory.
 
Even though minor intensity fluctuations are possible in the
short term, Calvin should continue to spin down as the cyclone 
traverses cooler waters Saturday while moving into a more
stable drier air mass.  The statistical-dynamical SHIPS models
agree that increasing southwesterly vertical shear should also be
an inhibiting factor by 96 hours.  Global model simulated 
infrared satellite imagery continues to show Calvin losing its 
organized convection early next week and the NHC forecast calls for 
the cyclone to degenerate to a post-tropical remnant low by day 5, 
if not sooner.  The intensity forecast indicates a faster 
rate of weakening through day 3 than the previous forecast, and 
closely follows the HCCA, IVCN, and LGEM intensity models, and is 
just below the Decay SHIPS.
 
The initial motion is estimated to be west-northwestward, or 285/14 
kt.  There is no change to the forecast philosophy.  The hurricane 
is expected to move within the deep east-southeasterly steering flow 
produced by a subtropical ridge stretching across the eastern 
Pacific through the period.  There continues to be quite a bit of 
uncertainty, with Calvin either passing near or over the Hawaiian 
Islands.  The global models have been trending poleward, either over 
or just to the north of the Big Island while along-track 
inconsistencies remain.  The most reasonable forecast approach is to 
hedge toward the best performing consensus aids HCCA and TVCE, and 
the official track forecast is based on this reliable method.  
Calvin is still expected to cross 140W and move into the central 
Pacific basin by early Monday morning, then approach the Hawaiian 
Islands on Tuesday and Wednesday.
 
Calvin's wind radii have been adjusted based on a RADARSAT (RCM 2)
15Jul 0245 UTC overpass.
 
 
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  15/0900Z 14.5N 127.5W   90 KT 105 MPH
 12H  15/1800Z 15.0N 129.7W   80 KT  90 MPH
 24H  16/0600Z 15.7N 132.6W   70 KT  80 MPH
 36H  16/1800Z 16.4N 135.5W   60 KT  70 MPH
 48H  17/0600Z 17.0N 138.6W   55 KT  65 MPH
 60H  17/1800Z 17.5N 142.0W   45 KT  50 MPH
 72H  18/0600Z 18.1N 145.5W   40 KT  45 MPH
 96H  19/0600Z 19.1N 152.7W   35 KT  40 MPH
120H  20/0600Z 20.5N 159.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Roberts
 
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