844
WTPA41 PHFO 312032
TCDCP1
TROPICAL STORM IONA DISCUSSION NUMBER 19
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012025
ISSUED BY NWS NATIONAL HURRICANE CENTER MIAMI FL
1100 AM HST THU JUL 31 2025
IONA IS STILL GENERATING A LARGE AREA OF STRONG BUT DISORGANIZED
CONVECTION OVER THE LOW-LEVEL CENTER. AN EARLIER PARTIAL SSMI/S
OVERPASS SUGGEST THE CONVECTION HAD POORLY-DEFINED BANDING, AND
THAT THE LOW-LEVEL CENTER MAY HAVE BECOME ELONGATED. SATELLITE
INTENSITY ESTIMATED HAVE INCREASED A LITTLE OVER THE PAST SEVERAL
HOURS AND NOW ARE IN THE 40-60 KT RANGE. THE INTENSITY WILL BE HELD
AT 45 KT FOR NOW.
THE INITIAL MOTION IS NOW 285/19 KT. IONA IS EXPECTED TO CONTINUE
WEST-NORTHWESTWARD WITH A DECREASE IN FORWARD SPEED FOR THE NEXT
TWO TO THREE DAYS AS IT MOVES ALONG ALONG THE SOUTHERN PERIPHERY OF
A LOW- TO MID-LEVEL SUBTROPICAL RIDGE LOCATED TO THE NORTH. AFTER
60-72 H, THE MODELS HAVE COME INTO BETTER AGREEMENT THAN IONA SHOULD
TURN NORTHWESTWARD TOWARD A BREAK IN THE SUBTROPICAL RIDGE WEST OF
160E, WITH THE FORMERLY MORE WESTWARD GFS JOINING THE MORE
NORTHWARD ECMWF/CANADIAN. THE MODEL GUIDANCE ENVELOPE HAS SHIFTED
TO THE RIGHT SINCE THE LAST ADVISORY, AND WHILE THE NEW FORECAST
TRACK IS ALSO SHIFTED TO THE RIGHT IT STILL LIES TO THE LEFT OF THE
CENTER OF THE ENVELOPE AND THE CONSENSUS MODELS.
IONA CONTINUES TO BE AFFECTED BY 20-25 KT OF NORTHWESTERLY SHEAR.
THIS SHOULD CONTINUE FOR THE NEXT 24 H OR SO, AND DURING THIS TIME
THE STORM IS EXPECTED TO WEAKEN SOME. SUBSEQUENTLY, THE SHEAR IS
FORECAST TO DECREASE, BUT THE GLOBAL MODELS FORECAST THE CYCLONE TO
MOVE CLOSE TO AN UPPER-LEVEL LOW OR TROUGH. IT IS NOT CLEAR AT THIS
TIME WHETHER THIS WILL BE FAVORABLE OR UNFAVORABLE FOR IONA TO
RE-INTENSIFY, AS SMALL CHANGES IN THE RELATIVE POSITIONS OF THE
SYSTEMS COULD MAKE A LARGE DIFFERENCE IN HOW MUCH INTENSIFICATION
MIGHT OCCUR. AFTER 96 H, THE GLOBAL MODELS AGREE THAT IONA SHOULD
WEAKEN, POSSIBLY DUE TO UPPER-LEVEL CONVERGENCE AND DRY AIR
ENTRAINMENT. IN CONTRAST, THE HAFS REGIONAL HURRICANE MODELS
FORECAST RE-INTENSIFICATION AT THAT TIME. OVERALL, THE INTENSITY
GUIDANCE HAS TRENDED HIGHER SINCE THE LAST ADVISORY. DUE TO THE
UNCERTAINTIES, THE NEW INTENSITY FORECAST WILL NOT YET MAKE
SIGNIFICANT CHANGES AND IS AN UPDATE OF THE PREVIOUS FORECAST.
HOWEVER, IT LIES NEAR THE LOWER END OF THE INTENSITY GUIDANCE.
FORECAST POSITIONS AND MAX WINDS
INIT 31/2100Z 13.2N 170.7W 45 KT 50 MPH
12H 01/0600Z 13.8N 173.4W 40 KT 45 MPH
24H 01/1800Z 14.6N 176.6W 35 KT 40 MPH
36H 02/0600Z 15.4N 179.4W 35 KT 40 MPH
48H 02/1800Z 16.4N 178.0E 35 KT 40 MPH
60H 03/0600Z 17.4N 175.8E 35 KT 40 MPH
72H 03/1800Z 18.4N 173.4E 35 KT 40 MPH
96H 04/1800Z 20.8N 169.1E 30 KT 35 MPH
120H 05/1800Z 23.4N 165.3E 30 KT 35 MPH...POST-TROP/REMNT LOW
FORECASTER BEVEN
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