Tropical Storm Calvin Discussion Number 20...Corrected
NWS National Hurricane Center Miami FL EP032023
500 AM HST Sun Jul 16 2023
Corrected timing in the key messages
The cloud pattern of Calvin has further deteriorated this morning.
The center is now exposed, and cloud tops have warmed over much of
the circulation with only a small area of moderate to deep
convection noted to the east of the center. The objective and
subjective satellite intensity estimates continue to quickly
decline, with a blend of the recent data suggesting that Calvin is
no longer a hurricane. Based on these data and its poor satellite
structure, the initial intensity is lowered to 60 kt.
The track forecast remains straightforward. Calvin is expected to
keep moving generally westward for the next several days as it is
steered by a well-established ridge over the eastern Pacific. This
motion will bring the cyclone into the central Pacific basin (west
of 140W) tonight or early Monday morning. Calvin is forecast to
approach the Hawaiian Islands on Tuesday and pass near or over the
Big Island of Hawaii early Wednesday. The track guidance remains in
good agreement on this overall scenario, although the details of its
track near Hawaii are still uncertain given the average amount of
cross-track spread in the guidance. The latest NHC forecast is
slightly faster and has been nudged slightly northward at 60-96 h,
but still lies near the center of the guidance envelope and close to
the HCCA and TVCE aids.
Calvin will move over 24 deg C waters and into a drier, more stable
environment during the next couple of days. Therefore, continued
weakening is anticipated, and the system could struggle to produce
convection on its trek into the central Pacific basin. As Calvin
moves closer to Hawaii, model-simulated satellite imagery suggests
it could produce some renewed bursts of convection to the north of
its center. This forecast keeps Calvin as a tropical cyclone through
72 h, although it could become post-tropical sooner if convection
collapses for an extended period. Regardless, there is good support
from both the global and hurricane models that Calvin will maintain
some tropical-storm-force winds (mainly to the north of its center)
as it nears Hawaii. With strong deep-layer southwesterly shear
expected in 96-120 h, this forecast shows Calvin opening into a
trough and dissipating by day 5.
KEY MESSAGES:
1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands during the next few days. A Tropical
Storm Watch could be issued for portions of the main Hawaiian
Islands later today, and interests in Hawaii should closely monitor
the latest forecast updates.
FORECAST POSITIONS AND MAX WINDS
INIT 16/1500Z 16.0N 134.8W 60 KT 70 MPH
12H 17/0000Z 16.4N 137.3W 55 KT 65 MPH
24H 17/1200Z 17.0N 140.6W 45 KT 50 MPH
36H 18/0000Z 17.5N 144.2W 45 KT 50 MPH
48H 18/1200Z 17.9N 147.9W 40 KT 45 MPH
60H 19/0000Z 18.6N 151.6W 40 KT 45 MPH
72H 19/1200Z 19.2N 155.0W 35 KT 40 MPH
96H 20/1200Z 20.1N 161.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 21/1200Z...DISSIPATED
$$
Forecaster Reinhart