CPAC: CALVIN - Post-Tropical - Discussion

[HurricaneEnzo]

That's more like it. No matter how many times it happens it always impresses me how the Big Island absolutely shreds anything trying to move in from the East.

[wxman57]

That's more like it. No matter how many times it happens it always impresses me how the Big Island absolutely shreds anything trying to move in from the East.

It wasn't the Big Island that shredded Calvin, it was a combination of wind shear and dry, sinking air. It's very hard to hit Hawaii from the east.

[Kingarabian]

That's more like it. No matter how many times it happens it always impresses me how the Big Island absolutely shreds anything trying to move in from the East.

It wasn't the Big Island that shredded Calvin, it was a combination of wind shear and dry, sinking air. It's very hard to hit Hawaii from the east.

It is, but the amount of attempts from the east have substantially increased over the past 9 years.

[wxman57]

What will CPHC do with Calvin in their next advisory? Recon clearly found an open wave with wind 30 kts or less. How can Calvin be a 45 kt TS? I think that Calvin was opening up into a wave late yesterday afternoon when it appeared to decouple. I've noticed that the NHC and CPHC typically do not like to indicate a storm is weakening as it nears land. Their main job is public safety, so they use an abundance (over abundance?) of caution in situations like this. I'm not faulting them with Calvin. What if Calvin's squalls suddenly returned as the center passed to the south overnight? They're in a tough spot with Calvin. However, our clients want to know what they should really expect when Calvin passes. For days, we've told our clients that Calvin would weaken to a remnant low, an open wave as it passed Hawaii.

[wxman57]

Interesting that CPHC mentions everything BUT SFMR observations for estimating Calvin's intensity. Why only consider FL wind and Dvorak estimates and not SFMR? You do not use a random FL wind outside of convection and reduce it to the surface when you have actual wind measurements in the area showing 30 kts or less. What about the lack of a closed circulation? I know, they don't want people to relax - just in case. It's frustrating when I have to keep Calvin a TS on our 18Z advisory only because CPHC refuses to acknowledge its true status. Hilo winds remain easterly at 8 kts. Total rainfall appears to be 2.44".

Deep convection around Calvin collapsed overnight, leaving residual
deep convection across east and southeast-facing shores and
slopes of the Big Island and Maui. This is the result of deep
tropical flow interacting with terrain. Calvin's low level
circulation center (LLCC) has become completely exposed, allowing
small corrections in initial position and movement for this
advisory. Instruments aboard the US Air Force Reserve's Hurricane
Hunter aircraft showed maximum flight level winds of 47 kt, reduced
to about 42 kt at sea level. Subjective Dvorak satellite analyses
from PHFO and JTWC gave current intensity numbers of 2.5, 35 kt and
2.0, 30 kt, respectively. UW-CIMSS derived an ADT intensity of
37 kt, while an ASCAT pass from last evening showed maximum winds
of about 40 kt within Calvin's northeast quadrant. Based on these
data, the initial intensity for this advisory has been decreased to
40 kt.

[cycloneye]

Tropical Storm Calvin Discussion Number 32
NWS Central Pacific Hurricane Center Honolulu HI EP032023
500 AM HST Wed Jul 19 2023

Deep convection around Calvin collapsed overnight, leaving residual
deep convection across east and southeast-facing shores and
slopes of the Big Island and Maui. This is the result of deep
tropical flow interacting with terrain. Calvin's low level
circulation center (LLCC) has become completely exposed, allowing
small corrections in initial position and movement for this
advisory. Instruments aboard the US Air Force Reserve's Hurricane
Hunter aircraft showed maximum flight level winds of 47 kt, reduced
to about 42 kt at sea level. Subjective Dvorak satellite analyses
from PHFO and JTWC gave current intensity numbers of 2.5, 35 kt and
2.0, 30 kt, respectively. UW-CIMSS derived an ADT intensity of
37 kt, while an ASCAT pass from last evening showed maximum winds
of about 40 kt within Calvin's northeast quadrant. Based on these
data, the initial intensity for this advisory has been decreased to
40 kt.

The initial motion for this advisory is unchanged at 275/17 kt as
Calvin continues to move south of a large subtropical ridge. No
significant change in this steering is expected over the next
several days. Calvin is about to complete its passage south of the
Big Island and the forecast track is essentially the same as the
previous forecast track, aside from small changes in initial
position and forward speed from tau 12 and beyond. The total track
is shorter as this system is forecast to dissipate at tau 60. The
forecast track remains within, but on the southern side, of the
guidance envelope. Although the center of Calvin is passing south of
the Big Island, much of the island remains within the 34 kt radius,
and impacts from strong winds, heavy rainfall, and high surf are
occurring.

The forecast calls for Calvin to finish its passage south of the
Big Island this morning, then continue moving westward away from
the main island chain as a weakening tropical storm. Vertical shear
affecting the tropical cyclone is expected to be moderate today,
then strong by tonight. The strong shear should result in
weakening to post-tropical/remnant low status late Thursday night.

KEY MESSAGES:

1. Calvin has almost completed its passage south of Hawaii County.
Expect periods of flash flooding, dangerous surf and damaging
winds. Calvin will continue to weaken as it moves westward to the
south of the other Hawaiian Islands today and tonight, bringing the
potential for some peripheral impacts.


FORECAST POSITIONS AND MAX WINDS

INIT 19/1500Z 17.8N 156.8W 40 KT 45 MPH
12H 20/0000Z 17.9N 159.5W 35 KT 40 MPH
24H 20/1200Z 18.1N 163.1W 35 KT 40 MPH
36H 21/0000Z 18.2N 166.8W 30 KT 35 MPH
48H 21/1200Z 18.2N 170.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 22/0000Z...DISSIPATED

$$
Forecaster Powell

[Kingarabian]

Interesting that CPHC mentions everything BUT SFMR observations for estimating Calvin's intensity. Why only consider FL wind and Dvorak estimates and not SFMR? You do not use a random FL wind outside of convection and reduce it to the surface when you have actual wind measurements in the area showing 30 kts or less. What about the lack of a closed circulation? I know, they don't want people to relax - just in case. It's frustrating when I have to keep Calvin a TS on our 18Z advisory only because CPHC refuses to acknowledge its true status. Hilo winds remain easterly at 8 kts. Total rainfall appears to be 2.44".

Deep convection around Calvin collapsed overnight, leaving residual
deep convection across east and southeast-facing shores and
slopes of the Big Island and Maui. This is the result of deep
tropical flow interacting with terrain. Calvin's low level
circulation center (LLCC) has become completely exposed, allowing
small corrections in initial position and movement for this
advisory. Instruments aboard the US Air Force Reserve's Hurricane
Hunter aircraft showed maximum flight level winds of 47 kt, reduced
to about 42 kt at sea level. Subjective Dvorak satellite analyses
from PHFO and JTWC gave current intensity numbers of 2.5, 35 kt and
2.0, 30 kt, respectively. UW-CIMSS derived an ADT intensity of
37 kt, while an ASCAT pass from last evening showed maximum winds
of about 40 kt within Calvin's northeast quadrant. Based on these
data, the initial intensity for this advisory has been decreased to
40 kt.

One of them will be on here soon to explain lol

[Sciencerocks]

[Yellow Evan]

ASCAT is probably enough to justify keeping Calvin at 40 knots. Orographic lifting is helping Calvin maintain deep convection for now but the end is near.

[wxman57]

ASCAT is probably enough to justify keeping Calvin at 40 knots. Orographic lifting is helping Calvin maintain deep convection for now but the end is near.

You don't use an ASCAT pass from 12 hours ago to estimate current intensity when you have actual reconnaissance in there.

[cycloneye]

Post-Tropical Cyclone Calvin Discussion Number 33
NWS Central Pacific Hurricane Center Honolulu HI EP032023
1100 AM HST Wed Jul 19 2023

Visible satellite imagery shows that Calvin's fully exposed low-
level center is becoming increasingly broad and ill-defined.
Subjective Dvorak fixes indicate that Calvin is too weak to
classify, and central convection has been absent for sufficiently
long that Calvin can safely be deemed post-tropical. Gale force
winds continue in the northern semicircle for now, but increased
vertical wind shear along the forecast track will prevent Calvin
from redeveloping. The updated forecast track lies close to the
well-performing HCCA and ECMWF guidance, with dissipation expected
in about 36 hours as the environment becomes increasingly hostile.

This is the last advisory issued by the Central Pacific Hurricane
Center on this system. Additional information on this system can be
found in High Seas Forecasts issued by the National Weather Service
in Honolulu, under AWIPS header HFOHSFNP, WMO header FZPN40 PHFO,
and online at weather.gov/hfo/HSFNP.


FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 17.9N 158.5W 35 KT 40 MPH...POST-TROPICAL
12H 20/0600Z 18.2N 161.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 20/1800Z 18.5N 165.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 21/0600Z...DISSIPATED

$$
Forecaster Birchard

[Iceresistance]

Is there a circulation from Calvin in there?


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