CPAC: IONA - Tropical Storm - Discussion

[REDHurricane]

So does anyone know whether or not this tsunami is going to have any effect on Iona? Has this scenario (tsunami from an 8.0+ magnitude earthquake hitting a major hurricane/super typhoon) ever even occurred before?

[cycloneye]

Hurricane Iona Discussion Number 12
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Tue Jul 29 2025

Iona likely reached peak intensity earlier today, with satellite
images now showing the eye obscured by a central dense overcast.
The cyclone has begun to weaken as it feels the influence of
increasing westerly vertical wind shear while also moving over
cooler sea surface temperatures below 27C, as depicted by the
Real-time, Global, Sea Surface Temperature Analysis. The latest
subjective Dvorak current intensity estimates from PHFO and JTWC
were 5.5/102 knots, while SAB was a somewhat lower 4.5/77 knots.
Meanwhile, the latest objective intensity estimates range from 85 to
96 knots. Given that the system has just recently begun to weaken,
the initial intensity will be lowered to 100 knots for this
advisory.

Iona is moving due west, or 270 degrees, at 15 knots. This general
motion is expected to continue during the next couple of days as the
cyclone moves along the southern periphery of a subtropical ridge to
the north. A turn toward the west-northwest and a gradual decrease
in forward speed is expected late in the week and over the weekend,
as the system is steered into a weakness in the mid-level ridge to
the north. The official track forecast remains near the center of
the tightly clustered guidance envelope and is nearly identical to
the previous advisory. Confidence remains high that Iona will stay
well south of the Hawaiian Islands.

The cyclone is expected to undergo rapid weakening tonight and
Wednesday as it experiences increasing westerly vertical wind shear
while also moving over cooler sea surface temperatures of 26.5 to
27C. A slower rate of weakening is then forecast Wednesday night
and Thursday. By Friday, the shear begins to relax, sea surface
temperatures begin to increase to 28C or above, and the mid-levels
begin to moisten. The spread among the intensity guidance is
considerable, and the cyclone’s intensity will likely depend on how
intact the system remains after moving through the hostile
environment over the next couple of days. The official forecast
shows the intensity leveling off after 48 hours, but confidence in
this is low. Overall, the intensity forecast lies pretty close to
the middle of the intensity guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 30/0300Z 11.0N 157.1W 100 KT 115 MPH
12H 30/1200Z 11.1N 159.5W 85 KT 100 MPH
24H 31/0000Z 11.3N 162.6W 70 KT 80 MPH
36H 31/1200Z 11.6N 166.0W 65 KT 75 MPH
48H 01/0000Z 12.1N 169.5W 60 KT 70 MPH
60H 01/1200Z 12.8N 172.7W 55 KT 65 MPH
72H 02/0000Z 13.7N 175.7W 55 KT 65 MPH
96H 03/0000Z 15.9N 179.2E 55 KT 65 MPH
120H 04/0000Z 17.9N 174.1E 50 KT 60 MPH

$$
Forecaster Jelsema (CPHC)

[gib]

So does anyone know whether or not this tsunami is going to have any effect on Iona? Has this scenario (tsunami from an 8.0+ magnitude earthquake hitting a major hurricane/super typhoon) ever even occurred before?

Tsunamis have long wavelengths and low amplitude in the open ocean. They aren't very noticeable until they reach shallow water. Iona won't be affected.

[cycloneye]

Hurricane Iona Discussion Number 13
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Tue Jul 29 2025

The satellite presentation has continued to deteriorate this
evening, with the low-level center of Iona obscured by a central
dense overcast with gradually warming cloud top temperatures. The
cyclone is continuing to be influenced by increasing westerly
vertical wind shear while also moving over cooler sea surface
temperatures around or slightly below 27C, as depicted by the
Real-time, Global, Sea Surface Temperature Analysis. The latest
subjective Dvorak current intensity estimates ranged from
4.5/77 knots to 5.5/102 knots, while the latest objective intensity
estimates range from 77 to 87 knots. Taking a blend of these data
the initial intensity has been lowered to 90 knots for this
advisory.

Iona is moving westward, or 275 degrees, at 15 knots. This general
motion is expected to continue during the next couple of days as the
cyclone moves along the southern periphery of a subtropical ridge to
the north. A turn toward the west-northwest and a gradual decrease
in forward speed is expected late in the week and over the weekend,
as the system is steered into a weakness in the mid-level ridge to
the north. The official track forecast remains near the center of
the tightly clustered guidance envelope and is very close to the
previous advisory. Confidence remains high that Iona will stay well
south of the Hawaiian Islands.

The cyclone is expected to undergo rapid weakening tonight and
Wednesday as it experiences increasing westerly vertical wind shear
while also moving over cooler sea surface temperatures of 26.5 to
27C. The intensity forecast then shows little change in strength
Thursday through Friday as sea surface temperatures begin to warm,
vertical wind shear gradually eases, and mid-level moisture
increases. Iona should then begin to gradually weaken by days 4
and 5 as the mid-levels dry out and the system becomes influenced by
increasing westerly and southwesterly vertical wind shear. The
official forecast was adjusted to account for the latest intensity
guidance trends, and lies pretty close to the middle of the guidance
envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 30/0900Z 11.3N 158.6W 90 KT 105 MPH
12H 30/1800Z 11.5N 161.0W 70 KT 80 MPH
24H 31/0600Z 11.8N 164.5W 55 KT 65 MPH
36H 31/1800Z 12.2N 168.2W 50 KT 60 MPH
48H 01/0600Z 12.9N 171.7W 50 KT 60 MPH
60H 01/1800Z 13.7N 175.1W 50 KT 60 MPH
72H 02/0600Z 14.5N 177.9W 50 KT 60 MPH
96H 03/0600Z 16.5N 177.3E 45 KT 50 MPH
120H 04/0600Z 18.8N 172.6E 40 KT 45 MPH

$$
Forecaster Jelsema (CPHC)

[cycloneye]

HAFs-A continues to intensify Iona at WPAC.

[StormWeather]

000
WTPA41 PHFO 301433
TCDCP1

Hurricane Iona Discussion Number 14
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
500 AM HST Wed Jul 30 2025

Iona has continued to rapidly weaken since the last advisory. A GPM
microwave overpass showed an exposed low-level center located well
to the northwest of the mid-level center apparent in geostationary
imagery, with little or no organized convection near the low-level
center. Subjective and objective satellite intensity estimates have
decreased significantly and currently are in the 45-75 kt range.
Based on a blend of these estimates, the initial intensity is
reduced to a likely generous 65 kt.

The initial motion is now 280/17 kt. This general motion is
expected to continue during the next day or two as the cyclone
moves along the southern periphery of a low- to mid-level
subtropical ridge to the north. A turn toward the west-northwest
and a gradual decrease in forward speed are expected late in the
week and over the weekend, as the system is steered into a weakness
in the ridge. The official forecast is nudged just a little north
of the previous track and lies near the center of the track
guidance envelope. Iona has stayed well south of the Hawaiian
Islands, and the cyclone is forecast to move farther away from the
islands during the next couple of days.

Rapid weakening is expected to continue for the next 12-24 h due to
increasing westerly vertical shear and a track over cooler sea
surface temperatures. After that, the intensity forecast shows a
period of little change in strength as sea surface temperatures
begin to warm along the forecast track and the atmospheric
conditions become a little more favorable. By the end of the
forecast period, Iona should again weaken as it encounters mid-level
dry air and another bout of vertical shear. The intensity forecast
was lowered below the previous forecast mainly in response to the
current intensity trends.


FORECAST POSITIONS AND MAX WINDS

INIT 30/1500Z 11.5N 160.2W 65 KT 75 MPH
12H 31/0000Z 11.8N 162.8W 55 KT 65 MPH
24H 31/1200Z 12.2N 166.4W 45 KT 50 MPH
36H 01/0000Z 12.8N 169.8W 45 KT 50 MPH
48H 01/1200Z 13.5N 173.2W 45 KT 50 MPH
60H 02/0000Z 14.5N 176.3W 45 KT 50 MPH
72H 02/1200Z 15.4N 179.2W 45 KT 50 MPH
96H 03/1200Z 17.3N 176.0E 40 KT 45 MPH
120H 04/1200Z 19.2N 171.1E 35 KT 40 MPH

$$
Forecaster Beven

[wxman57]

Looking more like a disorganized and weak TS than a hurricane. Jack is much more "generous" than I would be with its intensity.

[cycloneye]

Tropical Storm Iona Discussion Number 15
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
1100 AM HST Wed Jul 30 2025

Iona continues to rapidly weaken, as the low-level center is now
seen in visible imagery exposed well to the west-northwest of the
remaining poorly-organized convection. Subjective and objective
satellite intensity estimates again have decreased significantly
and currently are in the 40-65 kt range. Based on a blend of these
estimates, the initial intensity is reduced to a possibly generous
55 kt, and Iona is downgraded to a tropical storm.

The initial motion is 275/19 kt. There is little change in the
forecast philosophy from the past couple of forecasts, as a general
westward motion is expected to continue during the next day or two
while Iona moves along the southern periphery of a low- to mid-level
subtropical ridge to the north. A turn toward the west-northwest
and a gradual decrease in forward speed are expected after 48 h as
the system is steered into a weakness in the ridge. There has been
little change in the forecast guidance since the last advisory, and
the new forecast track is similar to the previous track.

Rapid weakening should continue for the next 12 h or so due to
westerly vertical shear and a track over cooler sea surface
temperatures. After that, the intensity forecast shows a period of
little change in strength as sea surface temperatures begin to warm
along the forecast track and the atmospheric conditions become a
little more favorable. After 72 h, Iona should again weaken as it
encounters mid-level dry air and another bout of vertical shear.
The intensity forecast was again lowered below the previous
forecast based on the current intensity trends. Note that the
intensity forecast is based on the premise that Iona will re-develop
enough convection to sustain the system as a tropical cyclone. If
this does not happen, the cyclone could degenerate to a remnant low
or trough before 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT 30/2100Z 11.7N 162.6W 55 KT 65 MPH
12H 31/0600Z 12.1N 165.5W 45 KT 50 MPH
24H 31/1800Z 12.7N 169.3W 40 KT 45 MPH
36H 01/0600Z 13.4N 172.7W 40 KT 45 MPH
48H 01/1800Z 14.1N 175.9W 40 KT 45 MPH
60H 02/0600Z 15.1N 178.8W 40 KT 45 MPH
72H 02/1800Z 16.0N 178.7E 40 KT 45 MPH
96H 03/1800Z 18.1N 174.1E 35 KT 40 MPH
120H 04/1800Z 20.2N 169.1E 30 KT 35 MPH

$$
Forecaster Beven

[StormWeather]

I’m just going say this: Adios Iona!