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Tropical Storm Iona Discussion Number  21
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Thu Jul 31 2025
 
Satellite imagery indicates that convection associated with Iona 
remains fragmented and poorly organized, with the low-level 
circulation center nearly exposed or located near the western edge 
of the deep convection due to persistent west-northwest shear. A 
recent AMSR2 microwave pass revealed an elongated low-level 
structure oriented from north to south, with no well-defined core. 
Subjective Dvorak current intensity estimates from HFO, SAB, and 
JTWC ranged from 2.5/35 kt to 3.0/45 kt. Based on these estimates 
and the poor satellite presentation, the initial intensity is 
lowered to 40 kt.

The initial motion is estimated at 285/16 kt. Iona is expected to 
continue moving west-northwestward over the next couple of days 
while gradually slowing, steered along the southern periphery of a 
subtropical ridge to the north. A turn toward the northwest is 
forecast by late this weekend or early next week as the system 
approaches a weakness in the ridge. The updated track forecast 
remains close to the previous one, with a slight rightward 
adjustment that aligns with the consensus guidance.

Little change in intensity is expected over the next day or two, but 
a steady weakening trend should begin by Sunday as the system 
interacts with an upper-level trough and entrains mid- to 
upper-level dry air. Most dynamical guidance suggests that Iona will 
gradually open into a trough by early next week. As such, the 
official forecast now shows the system dissipating by 96 hours, or 
Tuesday. This forecast assumes Iona will maintain sufficient 
convection to remain a tropical cyclone through the weekend. If 
convection fails to persist, however, dissipation could occur sooner 
than currently indicated.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  01/0900Z 14.2N 174.4W   40 KT  45 MPH
 12H  01/1800Z 14.8N 176.7W   40 KT  45 MPH
 24H  02/0600Z 15.8N 179.6W   40 KT  45 MPH
 36H  02/1800Z 17.0N 177.9E   40 KT  45 MPH
 48H  03/0600Z 18.1N 175.7E   35 KT  40 MPH
 60H  03/1800Z 19.5N 173.6E   35 KT  40 MPH
 72H  04/0600Z 21.3N 171.4E   30 KT  35 MPH
 96H  05/0600Z...DISSIPATED
 
$$
Forecaster Gibbs (CPHC)
 
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