238
WTPA41 PHFO 190240
TCDCP1
TROPICAL STORM CALVIN DISCUSSION NUMBER 30
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP032023
500 PM HST TUE JUL 18 2023
A BURST OF DEEP CONVECTION NORTH OF THE CENTER TODAY STRENGTHENED
CALVIN, AND A COUPLE OF PASSES THROUGH THE CIRCULATION BY
THE US AIR FORCE RESERVE'S HURRICANE HUNTERS SHOWED AN INCREASE IN
THE WINDS. SFMR SHOWED SOME PEAKS AT AROUND 55 KT, THOUGH THESE MAY
HAVE HAD SOME RAIN CONTAMINATION. THE ON-BOARD WEATHER OFFICER
INDICATED 48-50 KT MAY BE MORE REASONABLE. REDUCTION OF FLIGHT LEVEL
WINDS SHOWED 45-50 KT IN PORTIONS OF THE NORTHERN SEMICIRCLE. BASED
ON THESE DATA, THE INITIAL INTENSITY FOR THIS ADVISORY HAS BEEN
INCREASED TO 50 KT. THE AIRCRAFT DATA ALSO RESULTED IN AN INCREASE
IN THE 34 KT WIND RADII. THE RECENT STRENGTHENING MAY HAVE BEEN A
SHORT TERM TREND AS THE DEEP CONVECTION HAS EASED SINCE THIS MORNING
WITH CLOUD TOP TEMPERATURES WARMING THROUGH THE AFTERNOON.
THE INITIAL MOTION FOR THIS ADVISORY IS 275/18 KT AS CALVIN
CONTINUES TO MOVE SOUTH OF A LARGE 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 FORECAST FOR THIS ADVISORY IS
ESSENTIALLY ON THE PREVIOUS FORECAST TRACK BUT SLIGHTLY SLOWER AS A
REFLECTION OF THE SLOWER INITIAL MOTION. THE FORECAST TRACK ALSO
REMAINS ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE. ALTHOUGH THE
CENTER OF CALVIN IS EXPECTED TO PASS 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 EXPECTED.
ALTHOUGH CALVIN STRENGTHENED TODAY, THE DYNAMICAL MODELS SUGGEST
THAT THIS WAS A SHORT TERM CHANGE AND THE FORECAST STILL CALLS FOR
CALVIN TO PASS SOUTH OF THE BIG ISLAND AS A WEAKENING TROPICAL
STORM. VERTICAL SHEAR AFFECTING THE TROPICAL CYCLONE IS EXPECTED TO
BE MODERATE THROUGH TONIGHT AND INTO WEDNESDAY, THEN WILL QUICKLY
BECOME STRONG BY WEDNESDAY NIGHT. THE STRONG SHEAR SHOULD RESULT IN
A WEAKENING TO POST-TROPICAL/REMNANT LOW STATUS ON THURSDAY.
KEY MESSAGES:
1. CALVIN IS FORECAST TO PASS SOUTH OF HAWAII COUNTY TONIGHT,
BRINGING A PERIOD OF FLASH FLOODING, DANGEROUS SURF AND DAMAGING
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.
FORECAST POSITIONS AND MAX WINDS
INIT 19/0300Z 17.8N 153.3W 50 KT 60 MPH
12H 19/1200Z 18.4N 156.0W 45 KT 50 MPH
24H 20/0000Z 18.9N 159.8W 40 KT 45 MPH
36H 20/1200Z 19.4N 163.6W 35 KT 40 MPH
48H 21/0000Z 19.7N 167.5W 30 KT 35 MPH
60H 21/1200Z 19.9N 171.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 22/0000Z...DISSIPATED
FORECASTER KODAMA
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