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Tropical Storm Iona Discussion Number  17
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Wed Jul 30 2025
 
Satellite imagery indicates that convection has become more 
concentrated over the center of Iona, with a recent convective burst 
producing cloud tops as cold as -85 C. This burst has obscured the 
previously exposed low-level circulation center, though the overall 
structure generally remains disorganized. Subjective Dvorak current 
intensity estimates ranged from 2.5/35 kt (JTWC) to 3.0/45 kt (SAB), 
with HFO at 3.5/55 kt. These values are mostly consistent with 
objective satellite intensity estimates, which ranged from 30 to 40 
kt. Based on a blend of these estimates and the current satellite 
presentation, the initial intensity is held at 45 kt.

The initial motion is estimated at 280/20 kt. Iona is expected to 
continue moving westward over the next day or two along the southern 
periphery of a low- to mid-level subtropical ridge located to the 
north. By 48 to 60 hours, a gradual turn toward the west-northwest 
and a decrease in forward speed are anticipated as the system 
approaches a weakness in the ridge. The forecast track remains 
consistent with the previous advisory and is well supported by the 
latest consensus guidance.

Only slight additional weakening is expected in the short term as 
Iona remains embedded within a moderate westerly shear environment 
of 20 to 25 kt. By around 60 hours (Saturday), vertical shear is 
forecast to relax, which could allow the cyclone to hold steady or 
even briefly restrengthen as it moves over slightly warmer waters. 
However, conditions are expected to deteriorate again late this 
weekend through early next week, with increasing shear and mid-level 
dry air likely leading to weakening. The intensity forecast has been 
held steady from the the previous advisory, supported by the recent 
burst of convection and the latest guidance. This forecast assumes 
that Iona will maintain enough convection to remain a tropical 
cyclone, but if convection fails to persist, the system could 
degenerate into a remnant low sooner than currently indicated.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/0900Z 12.3N 166.9W   45 KT  50 MPH
 12H  31/1800Z 12.7N 169.8W   40 KT  45 MPH
 24H  01/0600Z 13.5N 173.3W   35 KT  40 MPH
 36H  01/1800Z 14.1N 176.7W   35 KT  40 MPH
 48H  02/0600Z 14.9N 179.6W   35 KT  40 MPH
 60H  02/1800Z 15.8N 177.9E   35 KT  40 MPH
 72H  03/0600Z 16.6N 175.7E   35 KT  40 MPH
 96H  04/0600Z 18.4N 171.3E   30 KT  35 MPH
120H  05/0600Z 20.5N 167.1E   30 KT  35 MPH
 
$$
Forecaster Gibbs (CPHC)
 
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