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Tropical Storm Iona Discussion Number   5
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Sun Jul 27 2025
 
The satellite presentation of Iona has improved this evening, with a
well-defined curved banding structure and excellent upper-level
outflow evident in all quadrants. A recent 28/0650Z Metop-C ASCAT
pass showed a few wind barbs near 40 knots. The latest subjective
Dvorak current intensity estimates came in at 3.0/45 knots from
PHFO, 3.0/45 knots from SAB, and 2.5/35 knots from JTWC. Objective
intensity estimates ranged from 42 to 49 knots. Taking a blend of
these data, the initial intensity for this advisory has been raised
to 45 knots, which may still be slightly conservative.
 
Tropical Storm Iona is moving westward at 270 degrees/10 knots. This
general motion is expected to continue over the next several days as
the cyclone moves along the southern periphery of a subtropical
ridge to the north. A gradual increase in forward speed is also
expected, due to a strengthening low- to mid-level ridge north of
the system. The track forecast remains closely aligned with a blend
of the FSSE, HCCA, and GFEX consensus guidance and is nearly
unchanged from the previous advisory. Confidence remains high that
Iona will stay well south of the Hawaiian Islands.
 
The environment appears conducive for further intensification over
the next day or so, as Iona remains over warm waters near 28C, with
adequate mid-level moisture and very light vertical wind shear. In
fact, the latest GFS and ECMWF SHIPS guidance indicates more than a
30 percent chance of a 25-knot increase in intensity over the next
24 hours. Given the current structure and favorable conditions, the
intensity forecast explicitly calls for rapid intensification during
the next 24 hours, with Iona expected to become a hurricane late
Monday or Monday night. Iona should reach peak intensity Monday
night or Tuesday, with steady weakening anticipated beginning
Tuesday night, as the system moves over slightly cooler waters,
begins to experience increasing westerly vertical wind shear, and
starts to entrain drier mid-level air. The cyclone is expected to
become a post-tropical remnant low by Day 5 and could potentially
weaken into a trough by that time. The intensity forecast has been
raised from the previous advisory to reflect the latest trends in
the guidance, and is best aligned with the FSSE and IVCN consensus
solutions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 10.9N 149.3W   45 KT  50 MPH
 12H  28/1800Z 10.9N 150.6W   55 KT  65 MPH
 24H  29/0600Z 10.9N 152.7W   70 KT  80 MPH
 36H  29/1800Z 11.0N 155.1W   75 KT  85 MPH
 48H  30/0600Z 11.2N 158.0W   65 KT  75 MPH
 60H  30/1800Z 11.6N 161.2W   55 KT  65 MPH
 72H  31/0600Z 12.0N 164.8W   45 KT  50 MPH
 96H  01/0600Z 12.9N 172.0W   35 KT  40 MPH
120H  02/0600Z 14.5N 179.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Jelsema (CPHC)
 
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