000
WTPA41 PHFO 300842
TCDCP1
 
Hurricane Iona Discussion Number  13
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Tue Jul 29 2025
 
The satellite presentation has continued to deteriorate this 
evening, with the low-level center of Iona obscured by a central 
dense overcast with gradually warming cloud top temperatures.  The 
cyclone is continuing to be influenced by increasing westerly 
vertical wind shear while also moving over cooler sea surface 
temperatures around or slightly below 27C, as depicted by the 
Real-time, Global, Sea Surface Temperature Analysis.  The latest 
subjective Dvorak current intensity estimates ranged from 
4.5/77 knots to 5.5/102 knots, while the latest objective intensity 
estimates range from 77 to 87 knots.  Taking a blend of these data 
the initial intensity has been lowered to 90 knots for this 
advisory.
 
Iona is moving westward, or 275 degrees, at 15 knots.  This general 
motion is expected to continue during the next couple of days as the 
cyclone moves along the southern periphery of a subtropical ridge to 
the north.  A turn toward the west-northwest and a gradual decrease 
in forward speed is expected late in the week and over the weekend, 
as the system is steered into a weakness in the mid-level ridge to 
the north.  The official track forecast remains near the center of 
the tightly clustered guidance envelope and is very close to the 
previous advisory. Confidence remains high that Iona will stay well 
south of the Hawaiian Islands.

The cyclone is expected to undergo rapid weakening tonight and 
Wednesday as it experiences increasing westerly vertical wind shear 
while also moving over cooler sea surface temperatures of 26.5 to 
27C.  The intensity forecast then shows little change in strength 
Thursday through Friday as sea surface temperatures begin to warm, 
vertical wind shear gradually eases, and mid-level moisture 
increases.  Iona should then begin to gradually weaken by days 4 
and 5 as the mid-levels dry out and the system becomes influenced by 
increasing westerly and southwesterly vertical wind shear.  The 
official forecast was adjusted to account for the latest intensity 
guidance trends, and lies pretty close to the middle of the guidance 
envelope.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 11.3N 158.6W   90 KT 105 MPH
 12H  30/1800Z 11.5N 161.0W   70 KT  80 MPH
 24H  31/0600Z 11.8N 164.5W   55 KT  65 MPH
 36H  31/1800Z 12.2N 168.2W   50 KT  60 MPH
 48H  01/0600Z 12.9N 171.7W   50 KT  60 MPH
 60H  01/1800Z 13.7N 175.1W   50 KT  60 MPH
 72H  02/0600Z 14.5N 177.9W   50 KT  60 MPH
 96H  03/0600Z 16.5N 177.3E   45 KT  50 MPH
120H  04/0600Z 18.8N 172.6E   40 KT  45 MPH
 
$$
Forecaster Jelsema (CPHC)