248
WTPA41 PHFO 310843
TCDCP1
TROPICAL STORM IONA DISCUSSION NUMBER 17
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012025
ISSUED BY NWS NATIONAL HURRICANE CENTER MIAMI FL
1100 PM HST WED JUL 30 2025
SATELLITE IMAGERY INDICATES THAT CONVECTION HAS BECOME MORE
CONCENTRATED OVER THE CENTER OF IONA, WITH A RECENT CONVECTIVE BURST
PRODUCING CLOUD TOPS AS COLD AS -85 C. THIS BURST HAS OBSCURED THE
PREVIOUSLY EXPOSED LOW-LEVEL CIRCULATION CENTER, THOUGH THE OVERALL
STRUCTURE GENERALLY REMAINS DISORGANIZED. SUBJECTIVE DVORAK CURRENT
INTENSITY ESTIMATES RANGED FROM 2.5/35 KT (JTWC) TO 3.0/45 KT (SAB),
WITH HFO AT 3.5/55 KT. THESE VALUES ARE MOSTLY CONSISTENT WITH
OBJECTIVE SATELLITE INTENSITY ESTIMATES, WHICH RANGED FROM 30 TO 40
KT. BASED ON A BLEND OF THESE ESTIMATES AND THE CURRENT SATELLITE
PRESENTATION, THE INITIAL INTENSITY IS HELD AT 45 KT.
THE INITIAL MOTION IS ESTIMATED AT 280/20 KT. IONA IS EXPECTED TO
CONTINUE MOVING WESTWARD OVER THE NEXT DAY OR TWO ALONG THE SOUTHERN
PERIPHERY OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE LOCATED TO THE
NORTH. BY 48 TO 60 HOURS, A GRADUAL TURN TOWARD THE WEST-NORTHWEST
AND A DECREASE IN FORWARD SPEED ARE ANTICIPATED AS THE SYSTEM
APPROACHES A WEAKNESS IN THE RIDGE. THE FORECAST TRACK REMAINS
CONSISTENT WITH THE PREVIOUS ADVISORY AND IS WELL SUPPORTED BY THE
LATEST CONSENSUS GUIDANCE.
ONLY SLIGHT ADDITIONAL WEAKENING IS EXPECTED IN THE SHORT TERM AS
IONA REMAINS EMBEDDED WITHIN A MODERATE WESTERLY SHEAR ENVIRONMENT
OF 20 TO 25 KT. BY AROUND 60 HOURS (SATURDAY), VERTICAL SHEAR IS
FORECAST TO RELAX, WHICH COULD ALLOW THE CYCLONE TO HOLD STEADY OR
EVEN BRIEFLY RESTRENGTHEN AS IT MOVES OVER SLIGHTLY WARMER WATERS.
HOWEVER, CONDITIONS ARE EXPECTED TO DETERIORATE AGAIN LATE THIS
WEEKEND THROUGH EARLY NEXT WEEK, WITH INCREASING SHEAR AND MID-LEVEL
DRY AIR LIKELY LEADING TO WEAKENING. THE INTENSITY FORECAST HAS BEEN
HELD STEADY FROM THE THE PREVIOUS ADVISORY, SUPPORTED BY THE RECENT
BURST OF CONVECTION AND THE LATEST GUIDANCE. THIS FORECAST ASSUMES
THAT IONA WILL MAINTAIN ENOUGH CONVECTION TO REMAIN A TROPICAL
CYCLONE, BUT IF CONVECTION FAILS TO PERSIST, THE SYSTEM COULD
DEGENERATE INTO A REMNANT LOW SOONER THAN CURRENTLY INDICATED.
FORECAST POSITIONS AND MAX WINDS
INIT 31/0900Z 12.3N 166.9W 45 KT 50 MPH
12H 31/1800Z 12.7N 169.8W 40 KT 45 MPH
24H 01/0600Z 13.5N 173.3W 35 KT 40 MPH
36H 01/1800Z 14.1N 176.7W 35 KT 40 MPH
48H 02/0600Z 14.9N 179.6W 35 KT 40 MPH
60H 02/1800Z 15.8N 177.9E 35 KT 40 MPH
72H 03/0600Z 16.6N 175.7E 35 KT 40 MPH
96H 04/0600Z 18.4N 171.3E 30 KT 35 MPH
120H 05/0600Z 20.5N 167.1E 30 KT 35 MPH
FORECASTER GIBBS (CPHC)
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