921
WTPA41 PHFO 010234
TCDCP1
TROPICAL STORM IONA DISCUSSION NUMBER 20
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012025
ISSUED BY NWS NATIONAL HURRICANE CENTER MIAMI FL
500 PM HST THU JUL 31 2025
SATELLITE IMAGERY INDICATES THAT CONVECTION ASSOCIATED WITH IONA
REMAINS DISORGANIZED, WITH WARMING CLOUD TOPS NOW NEAR -70 C, BUT
STILL POSITIONED OVER THE LOW-LEVEL CIRCULATION CENTER DESPITE
ONGOING MODERATE WEST-NORTHWEST SHEAR. HOWEVER, AN EARLIER ASCAT
PASS SUPPORTED PEAK WINDS NEAR 40 KT IN THE NORTHERN SEMICIRCLE, AND
A BLEND OF THE LATEST SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES
CONTINUES TO SUPPORT HOLDING THE INITIAL INTENSITY AT 45 KT.
THE INITIAL MOTION IS ESTIMATED AT 285/20 KT. IONA IS EXPECTED TO
CONTINUE MOVING WEST-NORTHWESTWARD DURING THE NEXT COUPLE OF DAYS,
WITH A GRADUAL DECREASE IN FORWARD SPEED AS IT REMAINS STEERED ALONG
THE SOUTHERN PERIPHERY OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE TO
THE NORTH. A TURN TOWARD THE NORTHWEST IS FORECAST LATE THIS WEEKEND
THROUGH EARLY NEXT WEEK AS THE SYSTEM APPROACHES A WEAKNESS IN THE
RIDGE. THE UPDATED TRACK FORECAST HAS BEEN ADJUSTED SLIGHTLY TO THE
RIGHT OF THE PREVIOUS FORECAST AND REPRESENTS A BLEND OF THE PRIOR
TRACK AND THE LATEST CONSENSUS GUIDANCE.
VERY LITTLE CHANGE WAS MADE TO THE INTENSITY FORECAST, AS MOST
GUIDANCE GENERALLY HOLDS IONA’S STRENGTH STEADY THROUGH THE WEEKEND
WHILE IT BEGINS TO TURN NORTHWESTWARD AND INTERACTS WITH AN
UPPER-LEVEL TROUGH. VERTICAL SHEAR MAY RELAX SOMEWHAT AFTER 24
HOURS, WHICH COULD ALLOW THE SYSTEM TO BRIEFLY MAINTAIN OR EVEN
SLIGHTLY INCREASE IN STRENGTH. HOWEVER, THERE IS CONSIDERABLE
UNCERTAINTY REGARDING HOW THE INTERACTION WITH THE TROUGH WILL
EVOLVE, AS SMALL DIFFERENCES IN POSITIONING COULD EITHER SUPPORT
MODEST STRENGTHENING OR ACCELERATE WEAKENING. DUE TO THIS
UNCERTAINTY, THE INTENSITY FORECAST MAINTAINS IONA AS A TROPICAL
STORM THROUGH THE WEEKEND, FOLLOWED BY GRADUAL WEAKENING AND
POSSIBLE DEGENERATION INTO A REMNANT LOW BY THE MIDDLE OF NEXT WEEK.
FORECAST POSITIONS AND MAX WINDS
INIT 01/0300Z 13.7N 172.7W 45 KT 50 MPH
12H 01/1200Z 14.3N 175.0W 45 KT 50 MPH
24H 02/0000Z 15.1N 177.9W 45 KT 50 MPH
36H 02/1200Z 16.1N 179.4E 45 KT 50 MPH
48H 03/0000Z 17.2N 177.2E 45 KT 50 MPH
60H 03/1200Z 18.4N 175.1E 45 KT 50 MPH
72H 04/0000Z 19.6N 172.9E 35 KT 40 MPH
96H 05/0000Z 22.8N 168.7E 30 KT 35 MPH
120H 06/0000Z 27.6N 165.5E 30 KT 35 MPH...POST-TROP/REMNT LOW
FORECASTER GIBBS (CPHC)
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page