CPAC: IONA - Tropical Storm - Discussion

[sasha_B]

Eye is clear on the latest frames & has been picked up by ADT as well. If this appearance holds for the next few hours (and factoring in the T5.5 that apparently came in after the last forecast discussion was written) there would be little reason not to go with 100 kts for the 06z Best Track point. The T4.0 fixes which (as stated in the discussion) influenced their decision to maintain Category 1 intensity were 6+ hours of very rapid intensification ago.

[Yellow Evan]

Iona is unprecedented, right? We haven’t had a homebrew CPAC storm become a hurricane in July before right?

Correct. Especially out of place for a non-El Nino years, which hasn't produced a homegrown CPAC TC of this strength since the mid 1980s.

[Yellow Evan]

As for the estimates, can we cool it a little the criticism? I wouldn't have gone 75 either but it's not a huge deal - it's no threat to land threat and I'm honestly not sure how much these forecasters are necessarily as focused on solely the intensity as posters in here.

[Yellow Evan]

A little convective asymmetries still but eye warmed hard after around 1z. Likely into the 960s at this point.

[Fancy1002]

Iona is looking pretty good, can’t wait to see her in the morning.

Also, does that look like a pinhole to anyone else?

[Yellow Evan]

Eye not fully cleared - once it does it’ll probably be around 10 nm.

[Yellow Evan]

TXPN41 PHFO 290558 AAA
TCSNP1
CENTRAL PACIFIC TROPICAL CYCLONE SUMMARY - FIXES
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI
0557 UTC TUE JUL 29 2025
A. HURRICANE IONA CP012025
B. 29/0530Z
C. 10.9N
D. 152.5W
E. GOES-18
F. T5.0/5.0/D2.0/24 HRS
G. IR/EIR
H. REMARKS...EYE FEATURE SHOWN ON IR IMAGERY WITH OW CENTER
SURROUNDING B RING YIELDS A DT OF 6.0. PT AGREES. MET HELD
TO 5.0 DUE TO CONSTRAINTS. FT 5.0 BASED ON CONSTRAINTS.
I. ADDL POSITIONS
NIL
$$
FORECASTER...BOHLIN

[Yellow Evan]

TPPZ01 PGTW 290542
A. HURRICANE 01C (IONA)
B. 29/0500Z
C. 10.82N
D. 152.48W
E. ONE/GOES18
F. T6.0/6.0/D3.5/24HRS STT: D0.5/03HRS
G. IR/EIR
H. REMARKS: 01A/PBO EYE/ANMTN. OW EYE SURROUNDED BY B YIELDS AN E# OF
5.5. ADDED 0.5 EYE ADJUSTMENT FOR W, TO YIELD A DT OF 6.0. MET YIELDS
4.0. PT YIELDS 5.0. DBO DT.
I. ADDITIONAL POSITIONS: NONE
TIMMERMAN

[ElectricStorm]

01C IONA 250729 0600 10.8N 152.6W CPAC 95 970

[Yellow Evan]

[Fancy1002]

Such a beautiful sight. Getting closer and closer to that classic buzzsaw look.

[cycloneye]

Hurricane Iona Discussion Number 9
NWS Central Pacific Hurricane Center Honolulu HI CP012025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Mon Jul 28 2025

Iona has a very impressive satellite presentation this evening, with
very cold cloud tops ranging from -70°C to -80°C surrounding the
well-defined eye. Subjective Dvorak current intensity estimates
came in at 5.0/90 knots from PHFO and 5.5/102 knots from SAB. The
ADT and AiDT objective intensity estimates from UW-CIMSS have ranged
between 97 and 104 knots over the past several hours. Based on a
blend of these data, the initial intensity for this advisory has
been increased to 100 knots, making Iona a Category 3 major
hurricane on the Saffir-Simpson hurricane wind scale.

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 conducive for further
intensification during the next 12 hours or so, as Iona will remain
over warm sea surface temperatures near 28C, with sufficient
mid-level moisture and minimal vertical wind shear. Given the
conducive environment, the intensity forecast calls for Iona to
reach category 4 status later tonight or early Tuesday. Steady
weakening is forecast to begin Tuesday night or Wednesday and
continue into the weekend, as the system moves over slightly cooler
waters, encounters increasing westerly vertical wind shear, and
begins to entrain drier mid-level air. 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 during the next 24 to 36 hours, and then
lies near or slightly below the intensity guidance envelope
thereafter.


FORECAST POSITIONS AND MAX WINDS

INIT 29/0900Z 10.8N 153.2W 100 KT 115 MPH
12H 29/1800Z 10.8N 155.0W 115 KT 130 MPH
24H 30/0600Z 10.8N 157.7W 110 KT 125 MPH
36H 30/1800Z 11.0N 161.0W 95 KT 110 MPH
48H 31/0600Z 11.3N 164.7W 80 KT 90 MPH
60H 31/1800Z 11.8N 168.4W 70 KT 80 MPH
72H 01/0600Z 12.6N 172.2W 60 KT 70 MPH
96H 02/0600Z 14.3N 178.6W 50 KT 60 MPH
120H 03/0600Z 16.5N 176.1E 40 KT 45 MPH

$$
Forecaster Jelsema (CPHC)

[Hurricane2022]

I'm sure this is 20 kts stronger than the CPHC estimates. I'd like to see what Papin would do and say with Iona, since the NHC is also issuing warnings on CPAC systems.

[Hurricane2022]

Iona is doing some wobbles and the eye is somewhat colder now. Looks like it is in the middle of an EWRC.

[Hayabusa]

Yes I know but can't help and notice that one outlier of an intense typhoon traveling west...

[cycloneye]

Yes, keeps going up.

CP, 01, 2025072912, , BEST, 0, 108N, 1537W, 110, 957, HU

[Kingarabian]

As for the estimates, can we cool it a little the criticism? I wouldn't have gone 75 either but it's not a huge deal - it's no threat to land threat and I'm honestly not sure how much these forecasters are necessarily as focused on solely the intensity as posters in here.

Criticism was pretty mild IMO and the CPHC does have a history.
Threat to land or not, a pinhole eye is never 75kts. It makes no sense to only adjust to a correct intensity unless there's a threat to land.

[Kingarabian]

Buzzsaw look and losing banding. Looks like its been a cat4 for the last 6 hours at least.

[cycloneye]

From now I say there will be revisions on the intensity when the TCR is made.

[sasha_B]

Eye is clear again and more symmetrical as of 1330z. It seems Iona may be recovering from the disruption that caused the eye to contract & cloud over earlier.