155
WTPA41 PHFO 190851
TCDCP1
TROPICAL STORM CALVIN DISCUSSION NUMBER 31
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP032023
1100 PM HST TUE JUL 18 2023
DEEP CONVECTION HAS DECREASED CONSIDERABLY NEAR THE CENTER OF
CALVIN SINCE LATE THIS AFTERNOON, BUT HAS BEGUN TO INCREASE FARTHER
TO THE NORTH ALONG WINDWARD SHORES AND SLOPES OF THE BIG ISLAND OF
HAWAII. THE LOW LEVEL CIRCULATION CENTER (LLCC) IS RAPIDLY BECOMING
UNVEILED AGAIN. INSTRUMENTS ABOARD THE US AIR FORCE RESERVE'S
HURRICANE HUNTER AIRCRAFT SHOWED MAXIMUM FLIGHT LEVEL WINDS OF 50
KT, REDUCED TO ABOUT 45 KT AT THE SURFACE. OBJECTIVE DVORAK
SATELLITE ANALYSES FROM PHFO AND JTWC GAVE CURRENT INTENSITY
NUMBERS OF 2.5 OR 35 KT. BASED ON THESE DATA, THE INITIAL INTENSITY
FOR THIS ADVISORY HAS BEEN DECREASED TO 45 KT.
THE INITIAL MOTION FOR THIS ADVISORY IS 275/17 KT AS CALVIN
CONTINUES TO MOVE SOUTH OF A LARGE SUBTROPICAL RIDGE. NO SIGNIFICANT
CHANGE IN THIS STEERING IS EXPECTED OVER THE NEXT SEVERAL DAYS.
AFTER PASSING SOUTH OF THE BIG ISLAND TONIGHT, THE FORECAST IS
ESSENTIALLY THE SAME AS THE PREVIOUS FORECAST TRACK BUT SLIGHTLY
TO THE SOUTH TO ACCOUNT FOR A SMALL ADJUSTMENT IN INITIAL POSITION,
THANKS TO THE NEWLY REVEALED LLCC. THE FORECAST TRACK LIES WITHIN,
BUT ON THE SOUTHERN SIDE, OF THE GUIDANCE ENVELOPE DUE TO THE
INITIAL POINT ADJUSTMENT. ALTHOUGH THE CENTER OF CALVIN IS PASSING
SOUTH OF THE BIG ISLAND, MOST OF THE ISLAND IS WELL WITHIN THE 34
KT RADIUS, AND IMPACTS FROM STRONG WINDS, HEAVY RAINFALL, AND HIGH
SURF ARE IMMINENT OR OCCURRING.
THE FORECAST CALLS FOR CALVIN TO PASS SOUTH OF THE BIG ISLAND, THEN
SOUTHWEST OF THE REST OF THE MAIN ISLAND CHAIN, AS A WEAKENING
TROPICAL STORM. VERTICAL SHEAR AFFECTING THE TROPICAL CYCLONE IS
EXPECTED TO BE MODERATE THROUGH TONIGHT AND INTO WEDNESDAY, THEN
STRONG BY WEDNESDAY NIGHT. THE STRONG SHEAR SHOULD RESULT IN A
WEAKENING TO POST-TROPICAL/REMNANT LOW STATUS ON THURSDAY.
KEY MESSAGES:
1. CALVIN HAS BEGUN TO PASS SOUTH OF HAWAII COUNTY. EXPECT PERIODS
OF FLASH FLOODING, DANGEROUS SURF AND DAMAGING WINDS. CALVIN WILL
WEAKEN AS IT MOVES WESTWARD TO THE SOUTH OF THE OTHER HAWAIIAN
ISLANDS WEDNESDAY AND WEDNESDAY NIGHT, BRINGING THE POTENTIAL FOR
SOME PERIPHERAL IMPACTS.
FORECAST POSITIONS AND MAX WINDS
INIT 19/0900Z 17.7N 155.2W 45 KT 50 MPH
12H 19/1800Z 17.8N 158.1W 45 KT 50 MPH
24H 20/0600Z 18.1N 161.9W 40 KT 45 MPH
36H 20/1800Z 18.3N 165.8W 35 KT 40 MPH
48H 21/0600Z 18.3N 169.7W 30 KT 35 MPH
60H 21/1800Z 18.0N 173.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 22/0600Z...DISSIPATED
FORECASTER POWELL
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