263
WTPA41 PHFO 010836
TCDCP1
TROPICAL STORM IONA DISCUSSION NUMBER 21
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012025
ISSUED BY NWS NATIONAL HURRICANE CENTER MIAMI FL
1100 PM HST THU JUL 31 2025
SATELLITE IMAGERY INDICATES THAT CONVECTION ASSOCIATED WITH IONA
REMAINS FRAGMENTED AND POORLY ORGANIZED, WITH THE LOW-LEVEL
CIRCULATION CENTER NEARLY EXPOSED OR LOCATED NEAR THE WESTERN EDGE
OF THE DEEP CONVECTION DUE TO PERSISTENT WEST-NORTHWEST SHEAR. A
RECENT AMSR2 MICROWAVE PASS REVEALED AN ELONGATED LOW-LEVEL
STRUCTURE ORIENTED FROM NORTH TO SOUTH, WITH NO WELL-DEFINED CORE.
SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES FROM HFO, SAB, AND
JTWC RANGED FROM 2.5/35 KT TO 3.0/45 KT. BASED ON THESE ESTIMATES
AND THE POOR SATELLITE PRESENTATION, THE INITIAL INTENSITY IS
LOWERED TO 40 KT.
THE INITIAL MOTION IS ESTIMATED AT 285/16 KT. IONA IS EXPECTED TO
CONTINUE MOVING WEST-NORTHWESTWARD OVER THE NEXT COUPLE OF DAYS
WHILE GRADUALLY SLOWING, STEERED ALONG THE SOUTHERN PERIPHERY OF A
SUBTROPICAL RIDGE TO THE NORTH. A TURN TOWARD THE NORTHWEST IS
FORECAST BY LATE THIS WEEKEND OR EARLY NEXT WEEK AS THE SYSTEM
APPROACHES A WEAKNESS IN THE RIDGE. THE UPDATED TRACK FORECAST
REMAINS CLOSE TO THE PREVIOUS ONE, WITH A SLIGHT RIGHTWARD
ADJUSTMENT THAT ALIGNS WITH THE CONSENSUS GUIDANCE.
LITTLE CHANGE IN INTENSITY IS EXPECTED OVER THE NEXT DAY OR TWO, BUT
A STEADY WEAKENING TREND SHOULD BEGIN BY SUNDAY AS THE SYSTEM
INTERACTS WITH AN UPPER-LEVEL TROUGH AND ENTRAINS MID- TO
UPPER-LEVEL DRY AIR. MOST DYNAMICAL GUIDANCE SUGGESTS THAT IONA WILL
GRADUALLY OPEN INTO A TROUGH BY EARLY NEXT WEEK. AS SUCH, THE
OFFICIAL FORECAST NOW SHOWS THE SYSTEM DISSIPATING BY 96 HOURS, OR
TUESDAY. THIS FORECAST ASSUMES IONA WILL MAINTAIN SUFFICIENT
CONVECTION TO REMAIN A TROPICAL CYCLONE THROUGH THE WEEKEND. IF
CONVECTION FAILS TO PERSIST, HOWEVER, DISSIPATION COULD OCCUR SOONER
THAN CURRENTLY INDICATED.
FORECAST POSITIONS AND MAX WINDS
INIT 01/0900Z 14.2N 174.4W 40 KT 45 MPH
12H 01/1800Z 14.8N 176.7W 40 KT 45 MPH
24H 02/0600Z 15.8N 179.6W 40 KT 45 MPH
36H 02/1800Z 17.0N 177.9E 40 KT 45 MPH
48H 03/0600Z 18.1N 175.7E 35 KT 40 MPH
60H 03/1800Z 19.5N 173.6E 35 KT 40 MPH
72H 04/0600Z 21.3N 171.4E 30 KT 35 MPH
96H 05/0600Z...DISSIPATED
FORECASTER GIBBS (CPHC)
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