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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)
 
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