565
WTPA41 PHFO 182039
TCDCP1
TROPICAL STORM CALVIN DISCUSSION NUMBER 29
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP032023
1100 AM HST TUE JUL 18 2023
A LARGE AREA OF DEEP CONVECTION DEVELOPED OVERNIGHT IN THE NORTHERN
SEMICIRCLE OF CALVIN'S CIRCULATION. THIS CONVECTION HAS PERSISTED
THROUGH THIS MORNING AND HAS OBSCURED THE LOW LEVEL CIRCULATION
CENTER THAT WAS SO CLEARLY VISIBLE YESTERDAY. FORTUNATELY, THE US
AIR FORCE RESERVE HAS A WC-130J FLYING A MISSION INTO THE SYSTEM
TODAY THAT HAS HELPED BETTER IDENTIFY THE SYSTEM'S CENTER AND
SURROUNDING WIND FIELD. SFMR DATA INDICATED 46 KT IN THE NE
QUADRANT AND A LARGE AREA OF WINDS AT OR ABOVE 34 KT. AS A RESULT,
THE INITIAL INTENSITY FOR THIS ADVISORY HAS BEEN INCREASED SLIGHTLY
TO 45 KT. THE 34 KT RADIUS IN THE NE QUADRANT HAS ALSO BEEN
INCREASED AS WELL.
THE INITIAL MOTION FOR THIS ADVISORY IS 280/19 KT AS CALVIN
CONTINUES TO MOVE SOUTH OF A SUBTROPICAL RIDGE. NO SIGNIFICANT
CHANGES IN THIS STEERING IS EXPECTED OVER THE NEXT SEVERAL DAYS.
THE MAIN OBJECTIVE AIDS HAVE THE CENTER OF CALVIN PASSING SOUTH OF
THE BIG ISLAND TONIGHT. THE TRACK FORECAST IS ESSENTIALLY THE SAME
AS THE PREVIOUS ADVISORY AND IS ON THE NORTHERN SIDE OF THE
GUIDANCE ENVELOPE, BUT STILL SOUTH OF THE BIG ISLAND.
THE OVERALL ENVIRONMENT AROUND CALVIN REMAINS DRY AND STABLE. CALVIN
IS CURRENTLY PASSING OVER SSTS OF 25-26C. ALONG THE FORECAST TRACK,
SSTS WILL BE GRADUALLY INCREASING AND WILL BE 26-27C AS CALVIN
PASSES THE BIG ISLAND. VERTICAL SHEAR AFFECTING THE TROPICAL CYCLONE
IS EXPECTED TO BE MODERATE THROUGH TONIGHT. THE LACK OF STRONG
VERTICAL SHEAR, AND THE WARMER SSTS SHOULD ALLOW CALVIN TO MAINTAIN
WINDS AT TROPICAL STORM INTENSITIES THROUGH WEDNESDAY. SHEAR LEVELS
SHOULD SIGNIFICANTLY INCREASE WEDNESDAY NIGHT ONWARD, AND SHOULD
RESULT IN A WEAKENING TO POST-TROPICAL/REMNANT LOW STATUS ON
THURSDAY.
KEY MESSAGES:
1. CALVIN IS FORECAST TO PASS VERY CLOSE TO HAWAII COUNTY TONIGHT,
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 DURING DAYLIGHT HOURS FOR IMPACTS PRIOR TO THE
ONSET OF TROPICAL STORM CONDITIONS, WHICH ARE EXPECTED TO START
THIS EVENING. THESE IMPACTS COULD INCLUDE FLASH FLOODING, DAMAGING
WINDS, AND LARGE AND DANGEROUS SURF.
FORECAST POSITIONS AND MAX WINDS
INIT 18/2100Z 17.8N 151.9W 45 KT 50 MPH
12H 19/0600Z 18.2N 154.3W 45 KT 50 MPH
24H 19/1800Z 18.8N 158.1W 40 KT 45 MPH
36H 20/0600Z 19.2N 161.8W 35 KT 40 MPH
48H 20/1800Z 19.5N 165.6W 30 KT 35 MPH
60H 21/0600Z 19.8N 169.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 21/1800Z...DISSIPATED
FORECASTER KODAMA
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