CPAC: IONA - Tropical Storm - Discussion

[Kingarabian]

Clearly a TC. Would love to see a CPAC MH fish. I think theyre up there as some of the best looking hurricanes world wide.

[StormWeather]

We are about to get Iona. 00Z ATCF went 35 kts.

Tropical Storm ONE
Updated July 28, 2025 at 00:00 UTC
Located at 10.9°N, 147.8°W
Minimum Pressure: 1005 mb
Maximum Winds: 35 kt
Radius of Maximum Wind: 20 nm
Environmental Pressure: 1011 mb
Storm Radius: 180 nm
Formerly Invest 90C
Satellite Loop
Radar Loop
Latest GFS Forecast
Latest ECMWF Forecast
Current

[StormWeather]

When this is named Iona at 5 PM HST, it will be the first time Iona has been used in the CPAC, as it replaced Iwa from 1982 after it was retired in the spring of 1983.

[cycloneye]

BULLETIN
Tropical Storm Iona Advisory Number 4
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Sun Jul 27 2025

...IONA BECOMES THE FIRST NAMED STORM OF THE SEASON IN THE CENTRAL
PACIFIC...


SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...10.9N 148.3W
ABOUT 960 MI...1545 KM SE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES


Tropical Storm Iona Discussion Number 4
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Sun Jul 27 2025

A strong burst of deep convection with very cold cloud tops below
-80C developed over the low-level center of the tropical cyclone
well southeast of the Hawaiian Islands earlier this morning into the
early afternoon. This activity has recently subsided, but the
satellite presentation has improved since the previous advisory,
with well-defined banding structures now evident. The latest
subjective Dvorak intensity estimates from PHFO, SAB, and JTWC all
came in at 2.5/35 knots, while the objective intensity estimates
ranged from 35 to 42 knots. Taking a blend of these data, the
initial intensity for this advisory has been raised to, perhaps a
conservative 35 knots, making Iona the first named storm of the
season in the central Pacific.

Tropical Storm Iona is moving westward at 270/9 knots. This general
westward motion is expected to continue during the next couple of
days as the system moves along the southern periphery of a
subtropical ridge to the north. By Tuesday night or Wednesday, Iona
is expected to increase its forward speed due to a strengthening
low-to-mid-level ridge north of the system. The track forecast
closely follows a blend of the FSSE and HCCA consensus guidance and
is very close to the track from the previous advisory. Confidence
remains high that Iona will stay well to the south of the Hawaiian
Islands.

The environment appears conducive to further intensification over
the next day or so, as Iona remains over warm waters around 28C,
with adequate mid-level moisture and very light vertical wind shear.
As a result, the intensity forecast calls for steady strengthening,
with the cyclone expected to near hurricane strength by Monday night
or Tuesday. However, by Tuesday night, Iona will begin to move over
slightly cooler waters, begin to feel the influence of increasing
westerly vertical wind shear, and start to entrain drier mid-level
air. This is expected to result in steady weakening, with the
cyclone likely becoming a post-tropical remnant low by Day 5 and
potentially weakening into a trough by that time. The intensity
forecast has been raised from the previous advisory, following the
latest trends in the intensity guidance, and is best aligned with
the FSSE and HCCA consensus guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 10.9N 148.3W 35 KT 40 MPH
12H 28/1200Z 11.0N 149.7W 45 KT 50 MPH
24H 29/0000Z 11.0N 151.7W 55 KT 65 MPH
36H 29/1200Z 11.0N 153.8W 60 KT 70 MPH
48H 30/0000Z 11.1N 156.4W 60 KT 70 MPH
60H 30/1200Z 11.5N 159.4W 50 KT 60 MPH
72H 31/0000Z 12.1N 162.9W 45 KT 50 MPH
96H 01/0000Z 13.0N 170.4W 35 KT 40 MPH
120H 02/0000Z 14.4N 177.4W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Jelsema (CPHC)

[Yellow Evan]

Nice low-level structure and outflow though not collectively vigorous.

[ElectricStorm]

All 4 hurricane models now have at least a Cat 1 hurricane, with HAFS-B being a major outlier with 135kts

Unlike the WPAC systems, this one is actually sustaining convection even though said convection isn't all that deep yet. Seems on its way to hurricane status unless dry air takes over

[cycloneye]

Up to 45kt.

CP, 01, 2025072806, , BEST, 0, 110N, 1488W, 45, 1001, TS

[Hayabusa]

Latest Euro survives this into the WPAC

[Hurricane2022]

NHC is now showing a 75 kt peak
And I hope HAFS-B is right!!!

[cycloneye]

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)

[cycloneye]

Iona has overachieved.

[Kingarabian]

Iona has overachieved.

https://i.imgur.com/jltHBCx.gif

Definitely has. Overall structure was great to begin with. Let's see if it can become a hurricane.

[Hayabusa]

06z, HFSA restrengthens at the end of the run

[cycloneye]

Will it cross the dateline into WPAC?

[Yellow Evan]

ATCF has 60 knots.

Convective structure resembles that of a compact intensfying system. Microwave has an inner core as well.

[Hayabusa]

Will it cross the dateline into WPAC?

It'd be interesting if it did in a non-El Nino year

[cycloneye]

Peak up to cat 2.

Hurricane Iona Discussion Number 6
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
500 AM HST Mon Jul 28 2025

Iona has continued to become better organized overnight with a
couple of recent microwave images depicting a well-defined low- to
mid-level eye feature. Recent geostationary satellite imagery has
shown what appears to be a banded-type eye becoming apparent. The
latest subjective satellite intensity estimates were T4.0/65 kt from
SAB, T3.5/55 kt from PHFO, and T3.0/45 kt from JTWC. Given the
recent improvement in structure as seen in the microwave images, the
initial intensity is increased to 65 kt, making Iona the first
hurricane in the Central Pacific basin of the 2025 hurricane season.

Iona remains in an environment favorable for strengthening. The
cyclone is over SSTs of around 28C, and the shear is forecast to
remain 10 kt or less during the next 24 to 36 hours. The only
inhibiting factor appears to be some drier mid-level air in the
surrounding environment. Given these conditions, steady to
possibly rapid strengthening is anticipated during the next 24 to
36 hours, and the official intensity forecast again shows a
higher peak than the previous advisory. After 36 hours, slightly
lower SSTs and an increase in vertical wind shear are likely to
result in gradual weakening throughout much of the remainder of the
forecast period. The updated intensity forecast is in good
agreement with the FSSE, HCCA, and IVCN consensus aids, and is
close to the peak shown by most of the regional hurricane models.

The storm is moving westward or 270 degrees at around 10 kt. There
has been no change in the track forecast reasoning. Iona should
continue to move westward along the southern side of a mid-level
ridge during the next couple of days. After that time, a faster
west-northwestward motion is expected as Iona reaches the
southwestern portion of the ridge. The updated track forecast is
very similar to the previous advisory and is a blend of the various
track consensus aids. Confidence remains high that Iona will stay
well south of the Hawaiian Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 28/1500Z 10.7N 150.1W 65 KT 75 MPH
12H 29/0000Z 10.7N 151.7W 75 KT 85 MPH
24H 29/1200Z 10.7N 153.8W 85 KT 100 MPH
36H 30/0000Z 10.8N 156.4W 85 KT 100 MPH
48H 30/1200Z 11.0N 159.5W 75 KT 85 MPH
60H 31/0000Z 11.4N 162.9W 65 KT 75 MPH
72H 31/1200Z 11.8N 166.4W 55 KT 65 MPH
96H 01/1200Z 12.9N 173.7W 45 KT 50 MPH
120H 02/1200Z 14.6N 179.1E 35 KT 40 MPH

$$
Forecaster Brown

[Iceresistance]

I wasn't expecting Iona to become a hurricane, this surely wasn't on my Bingo Card

[Yellow Evan]

Will it cross the dateline into WPAC?

If this becomes strong enough in the next 24 hours to erode the ULL/TUTT, yes.

[TomballEd]

Looking at the satellite loop, 65 knots could be a smidge generous. Whatever computer figures the ADT agrees with me.




UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 9.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 28 JUL 2025 Time : 144021 UTC
Lat : 10:41:59 N Lon : 150:03:02 W


CI# /Pressure/ Vmax
2.7 /1007.8mb/ 39.0kt