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Hurricane Iona Discussion Number   8
NWS Central Pacific Hurricane Center Honolulu HI   CP012025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Mon Jul 28 2025
 
The satellite presentation of Iona has improved since earlier today, 
with very cold cloud tops ranging from -70°C to -80°C surrounding a
developing eye that is becoming increasingly well-defined. 
Subjective Dvorak current intensity estimates came in at 4.0/65 
knots from PHFO, 4.0/65 knots from SAB, and 4.5/77 knots from JTWC. 
Objective estimates from ADT, AiDT, and SATCON have ranged between 
65 and 82 knots over the past several hours. Based on a blend of 
these data, the initial intensity for this advisory has been 
increased to 75 knots.

Hurricane Iona is moving due west, or 270 degrees at 11 knots. This
general motion, along with a gradual increase in forward speed, 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
turn toward the west-northwest is anticipated by late in the week as
the system is influenced by a weakness in the mid-level ridge,
created by a developing upper-level low west of the International
Date Line.  The official track forecast remains near the center of
the guidance envelope and is nearly identical to the previous
advisory.  Confidence remains high that Iona will stay well south of
the Hawaiian Islands.
 
Environmental conditions appear primed for further intensification 
during the next 24 hours.  Iona will remain over warm sea surface 
temperatures near 28C, with sufficient mid-level moisture and 
minimal vertical wind shear.  The latest ECMWF SHIPS guidance 
indicates a greater than a 40 percent probability of a 30-knot 
intensity increase within 24 hours.  Given the improving structure 
and conducive environment, the intensity forecast explicitly calls 
for rapid intensification during the next 24 hours, with Iona 
expected to become a major hurricane on Tuesday.  Steady weakening 
is forecast to begin Tuesday night or Wednesday as the system moves 
over slightly cooler waters, encounters increasing westerly vertical 
wind shear, and begins to entrain drier mid-level air.  Iona is 
expected to weaken to tropical depression status by day 5, and it is 
possible the system could become a post-tropical remnant low by that 
time.  The intensity forecast has been adjusted slightly upward from 
the previous advisory, reflecting the latest trends in the intensity 
guidance.  This aligns well with regional hurricane models through 
day 2 and then closely follows the HCCA consensus guidance 
thereafter.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0300Z 10.9N 152.2W   75 KT  85 MPH
 12H  29/1200Z 10.9N 153.8W   95 KT 110 MPH
 24H  30/0000Z 10.9N 156.3W  105 KT 120 MPH
 36H  30/1200Z 10.9N 159.3W   95 KT 110 MPH
 48H  31/0000Z 11.2N 162.9W   75 KT  85 MPH
 60H  31/1200Z 11.5N 166.7W   60 KT  70 MPH
 72H  01/0000Z 12.1N 170.4W   50 KT  60 MPH
 96H  02/0000Z 13.7N 178.0W   40 KT  45 MPH
120H  03/0000Z 15.9N 176.5E   35 KT  40 MPH
 
$$
Forecaster Jelsema (CPHC)
 
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