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Tropical Storm Iona Discussion Number  19
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
1100 AM HST Thu Jul 31 2025

Iona is still generating a large area of strong but disorganized 
convection over the low-level center.  An earlier partial SSMI/S 
overpass suggest the convection had poorly-defined banding, and 
that the low-level center may have become elongated. Satellite 
intensity estimated have increased a little over the past several 
hours and now are in the 40-60 kt range. The intensity will be held 
at 45 kt for now.
 
The initial motion is now 285/19 kt. Iona is expected to continue
west-northwestward with a decrease in forward speed for the next 
two to three days as it moves along along the southern periphery of 
a low- to mid-level subtropical ridge located to the north. After 
60-72 h, the models have come into better agreement than Iona should 
turn northwestward toward a break in the subtropical ridge west of 
160E, with the formerly more westward GFS joining the more 
northward ECMWF/Canadian.  The model guidance envelope has shifted 
to the right since the last advisory, and while the new forecast 
track is also shifted to the right it still lies to the left of the 
center of the envelope and the consensus models.

Iona continues to be affected by 20-25 kt of northwesterly shear.
This should continue for the next 24 h or so, and during this time 
the storm is expected to weaken some.  Subsequently, the shear is 
forecast to decrease, but the global models forecast the cyclone to 
move close to an upper-level low or trough. It is not clear at this 
time whether this will be favorable or unfavorable for Iona to 
re-intensify, as small changes in the relative positions of the 
systems could make a large difference in how much intensification 
might occur.  After 96 h, the global models agree that Iona should 
weaken, possibly due to upper-level convergence and dry air 
entrainment. In contrast, the HAFS regional hurricane models 
forecast re-intensification at that time. Overall, the intensity 
guidance has trended higher since the last advisory. Due to the 
uncertainties, the new intensity forecast will not yet make 
significant changes and is an update of the previous forecast. 
However, it lies near the lower end of the intensity guidance.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 13.2N 170.7W   45 KT  50 MPH
 12H  01/0600Z 13.8N 173.4W   40 KT  45 MPH
 24H  01/1800Z 14.6N 176.6W   35 KT  40 MPH
 36H  02/0600Z 15.4N 179.4W   35 KT  40 MPH
 48H  02/1800Z 16.4N 178.0E   35 KT  40 MPH
 60H  03/0600Z 17.4N 175.8E   35 KT  40 MPH
 72H  03/1800Z 18.4N 173.4E   35 KT  40 MPH
 96H  04/1800Z 20.8N 169.1E   30 KT  35 MPH
120H  05/1800Z 23.4N 165.3E   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Beven
 
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