579
WTPA41 PHFO 180859
TCDCP1
TROPICAL STORM CALVIN DISCUSSION NUMBER 27
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP032023
1100 PM HST MON JUL 17 2023
THE MOST RECENT CONVENTIONAL INFRARED SATELLITE IMAGERY CONTINUES
TO SHOW THE PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
OF TROPICAL STORM CALVIN. DEEP CONVECTION HAS BEEN DEVELOPING
NORTH OF THE LLCC DURING THE PAST SEVERAL HOURS. AN AIRCRAFT
FROM THE 53RD WEATHER RECONNAISSANCE SQUADRON "HURRICANE HUNTERS"
IS CURRENTLY SAMPLING TROPICAL STORM CALVIN AS IT CONTINUES TO
MOVE RAPIDLY TOWARD THE BIG ISLAND OF HAWAII LATE THIS EVENING.
THEIR FLIGHT-LEVEL DATA SUPPORT TROPICAL STORM FORCE WINDS WITH
THIS SYSTEM. RECENT SATELLITE-BASED SCATTEROMETER PASSES ALSO SHOW
WINDS OF AT LEAST 35 KT OVER A BROAD SWATH NORTH AND NORTHEAST OF
THE CENTER. THE MOST RECENT SUBJECTIVE DVORAK SATELLITE INTENSITY
ESTIMATES WERE 35 KT FROM PHFO AND JTWC. THE CURRENT CIMSS SATCON
ESTIMATE SHOWS 41 KT. THE INITIAL INTENSITY FOR THIS ADVISORY IS
MAINTAINED AT 40 KT BASED ON A BLEND OF THESE ESTIMATES.
CALVIN'S INITIAL MOTION FOR THIS ADVISORY IS 275/19 KT AS THE
CYCLONE CONTINUES TO BE STEERED RAPIDLY WESTWARD SOUTH OF A LARGE
SUBTROPICAL RIDGE. THIS STEERING IS EXPECTED TO CONTINUE OVER THE
NEXT 3 TO 4 DAYS. THE DYNAMICAL GUIDANCE INDICATES THAT THE CENTER
OF CALVIN WILL PASS OVER, OR JUST SOUTH OF THE BIG ISLAND TUESDAY
NIGHT. THE LATEST TRACK FORECAST IS CLOSE TO THE PREVIOUS
FORECAST, WHICH CONTINUES TO CLOSELY FOLLOW THE HCCA GUIDANCE.
THE SURROUNDING ENVIRONMENT AROUND CALVIN CONTINUES TO BE
RELATIVELY DRY AND STABLE. THE SSTS ARE GRADUALLY INCREASING TO
AROUND 25C, AND WE EXPECT ADDITIONAL WARMING OF THE SSTS TO 26-27C
AS IT MOVES CLOSER TO THE MAIN HAWAIIAN ISLANDS. THE HIGHER SSTS
MAY SUPPORT ADDITIONAL DEEP CONVECTION SPREADING AROUND THE
NORTHERN SEMICIRCLE OF CALVIN DURING THE NEXT DAY OR TWO. THIS IS
EXPECTED TO KEEP THE CYCLONE AT TROPICAL STORM INTENSITY BY THE
TIME IT REACHES THE BIG ISLAND. AS A RESULT, A TROPICAL STORM
WARNING REMAINS IN EFFECT FOR HAWAII COUNTY. AFTER IT PASSES
SOUTHWEST OF THE MAIN HAWAIIAN ISLANDS, WE EXPECT IT TO MOVE NEAR
AN UPPER TROPOSPHERIC TROUGH IN ABOUT 36-48 HRS. THIS FEATURE ALOFT
WILL LIKELY INCREASE THE VERTICAL WIND SHEAR OVER THE SYSTEM, AND
WILL EVENTUALLY RESULT IN IT BECOMING A POST-TROPICAL/REMNANT LOW
BY WEDNESDAY NIGHT OR THURSDAY.
KEY MESSAGES:
1. CALVIN IS FORECAST TO PASS OVER OR VERY CLOSE TO HAWAII COUNTY
TUESDAY NIGHT, BRINGING A PERIOD OF HEAVY RAIN, HIGH SURF AND
LOCALLY STRONG WINDS. CALVIN IS EXPECTED TO WEAKEN AS IT MOVES
WESTWARD TO THE SOUTH OF THE OTHER HAWAIIAN ISLANDS WEDNESDAY
AND WEDNESDAY NIGHT, BRINGING THE POTENTIAL FOR SOME PERIPHERAL
IMPACTS.
2. IT IS IMPORTANT TO NOT FOCUS ON THE EXACT FORECAST TRACK AND
INTENSITY WHEN PREPARING FOR CALVIN. PERSONS IN HAWAII COUNTY
SHOULD PREPARE FROM NOW THROUGH TUESDAY AFTERNOON FOR IMPACTS
PRIOR TO THE ONSET OF TROPICAL STORM CONDITIONS. THESE IMPACTS
COULD INCLUDE FLASH FLOODING, DAMAGING WINDS, AND LARGE AND
DANGEROUS SURF.
FORECAST POSITIONS AND MAX WINDS
INIT 18/0900Z 17.4N 147.5W 40 KT 45 MPH
12H 18/1800Z 17.8N 150.4W 40 KT 45 MPH
24H 19/0600Z 18.5N 154.2W 35 KT 40 MPH
36H 19/1800Z 19.1N 158.0W 35 KT 40 MPH
48H 20/0600Z 19.6N 161.7W 30 KT 35 MPH
60H 20/1800Z 19.8N 165.3W 25 KT 30 MPH
72H 21/0600Z 20.1N 169.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 22/0600Z...DISSIPATED
FORECASTER HOUSTON
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