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Hurricane Iona Discussion Number  12
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Tue Jul 29 2025
 
Iona likely reached peak intensity earlier today, with satellite 
images now showing the eye obscured by a central dense overcast.  
The cyclone has begun to weaken as it feels the influence of 
increasing westerly vertical wind shear while also moving over 
cooler sea surface temperatures below 27C, as depicted by the 
Real-time, Global, Sea Surface Temperature Analysis.  The latest 
subjective Dvorak current intensity estimates from PHFO and JTWC 
were 5.5/102 knots, while SAB was a somewhat lower 4.5/77 knots. 
Meanwhile, the latest objective intensity estimates range from 85 to 
96 knots.  Given that the system has just recently begun to weaken, 
the initial intensity will be lowered to 100 knots for this 
advisory.

Iona is moving due west, or 270 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 nearly identical 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. A slower rate of weakening is then forecast Wednesday night 
and Thursday.  By Friday, the shear begins to relax, sea surface 
temperatures begin to increase to 28C or above, and the mid-levels 
begin to moisten. The spread among the intensity guidance is 
considerable, and the cyclone’s intensity will likely depend on how 
intact the system remains after moving through the hostile 
environment over the next couple of days. The official forecast 
shows the intensity leveling off after 48 hours, but confidence in 
this is low. Overall, the intensity forecast lies pretty close to 
the middle of the intensity guidance envelope.   
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0300Z 11.0N 157.1W  100 KT 115 MPH
 12H  30/1200Z 11.1N 159.5W   85 KT 100 MPH
 24H  31/0000Z 11.3N 162.6W   70 KT  80 MPH
 36H  31/1200Z 11.6N 166.0W   65 KT  75 MPH
 48H  01/0000Z 12.1N 169.5W   60 KT  70 MPH
 60H  01/1200Z 12.8N 172.7W   55 KT  65 MPH
 72H  02/0000Z 13.7N 175.7W   55 KT  65 MPH
 96H  03/0000Z 15.9N 179.2E   55 KT  65 MPH
120H  04/0000Z 17.9N 174.1E   50 KT  60 MPH
 
$$
Forecaster Jelsema (CPHC)
 
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