CPAC: CALVIN - Post-Tropical - Discussion

[cycloneye]

Hurricane Calvin Discussion Number 13
NWS National Hurricane Center Miami FL EP032023
1100 AM HST Fri Jul 14 2023

The satellite appearance of Calvin remains impressive this
afternoon. Its well-defined eye is surrounded by a ring of deep,
cold convective cloud tops, and visible satellite imagery shows
healthy upper-level anticyclonic outflow in all quadrants of the
hurricane. While some drier mid-level air appears to be wrapping
around the southern and eastern portions of the circulation,
Calvin's inner core still appears intact at this time. The various
objective and subjective satellite estimates range from 106-115 kt,
and the initial intensity is raised to 110 kt for this advisory.
Some of the initial wind radii values were adjusted based on a
recently processed 1402 UTC RCM-3 synthetic aperture radar overpass
over Calvin.

Although some small intensity fluctuations cannot be ruled out in
the near term, Calvin is likely near its peak intensity. The
hurricane is expected to move over cooler waters tomorrow and into a
drier, more stable environment through early next week. Calvin
should also encounter some increased southwesterly vertical wind
shear later in the forecast period. Therefore, weakening is forecast
to begin tomorrow and continue into next week. The convective
structure of Calvin later in the forecast period is a source of
uncertainty, with the hurricane models (HAFS-A/B) showing more of a
TC-like structure while the global models (GFS and ECMWF) show it
almost devoid of convection. For now, the forecast does not show
Calvin becoming post-tropical until day 5. The latest intensity
forecast remains on the high end of the guidance envelope through 48
h, then closely follows the multi-model consensus aids thereafter.

The hurricane is moving west-northwestward at 285/14 kt. This
general motion will continue for the next several days as Calvin is
steered by a mid-level ridge that extends westward across the
eastern subtropical Pacific. Once again, the track models are in
good agreement on this scenario. The updated NHC forecast is very
similar to the previous one, but just a bit slower at days 3-5
based on the latest model consensus trends. Calvin is expected to
cross 140W and move into the central Pacific basin by early Monday
morning, then approach the Hawaiian Islands on Tuesday and
Wednesday.


KEY MESSAGES:

1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands early next week. It is too early to
determine the exact location and magnitude of potential impacts
given uncertainties in the track, intensity, and structure of Calvin
as it approaches the islands. Interests in Hawaii should closely
monitor the latest forecast updates.


FORECAST POSITIONS AND MAX WINDS

INIT 14/2100Z 13.8N 124.6W 110 KT 125 MPH
12H 15/0600Z 14.3N 126.7W 105 KT 120 MPH
24H 15/1800Z 15.1N 129.5W 100 KT 115 MPH
36H 16/0600Z 15.7N 132.4W 90 KT 105 MPH
48H 16/1800Z 16.3N 135.5W 75 KT 85 MPH
60H 17/0600Z 16.9N 138.5W 60 KT 70 MPH
72H 17/1800Z 17.4N 141.9W 50 KT 60 MPH
96H 18/1800Z 18.3N 149.1W 40 KT 45 MPH
120H 19/1800Z 19.0N 156.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Reinhart

[Yellow Evan]

Fading now.

[Kingarabian]

Euro keeps it a weak TS but intact all the way until it reaches the Big Island. Could be a solid rain maker.

[Yellow Evan]

Euro keeps it a weak TS but intact all the way until it reaches the Big Island. Could be a solid rain maker.

Considering the pending Nino, drought buster as well.

[Sciencerocks]

[ElectricStorm]

Eye has filled in and CDO has warmed considerably. 0z best track is still at 105kts but it's probably not a major anymore. Maybe 90-95kts max

[Sciencerocks]

[cycloneye]

Hurricane Calvin Discussion Number 14
NWS National Hurricane Center Miami FL EP032023
500 PM HST Fri Jul 14 2023

Calvin has become a bit less organized since the last advisory, with
the eye becoming less distinct in satellite imagery and the cloud
tops in the eyewall becoming warmer. This is likely due to a
combination of the hurricane passing over the 26C sea surface
temperature isotherm and hints of an outer eyewall seen in a 0023
UTC SSM/IS overpass. Various subjective and objective satellite
intensity estimates are in the 100-115 kt range, and based on the
current trends in satellite imagery the initial intensity is reduced
to 105 kt.

Calvin has likely peaked in intensity, and it should weaken steadily
during the next 48 hours as sea surface temperatures under the
forecast track decrease to near 24C. The intensity forecast is less
clear cut after 48 h. While the consensus of the guidance indicates
that Calving should continue to weaken due to increasing
southwesterly vertical shear and dry air entrainment, the sea
surface temperatures along the forecast track increase from 48 to
120 h. Thus, it cannot be ruled out that the cyclone will weaken
more slowly than currently forecast in the later part of the
forecast period. Overall, the new intensity forecast follows the
trend of the intensity guidance and has only minor adjustments from
the previous forecast.

The initial motion remains 285/14 kt, and this general motion should
continue for the next several days as Calvin is steered by a low- to
mid-level ridge that extends westward across the eastern subtropical
Pacific. There has been little change in the track guidance since
the previous advisory. Thus, the new forecast track is similar to
the previous track and lies near the various consensus models.
Calvin is still expected to cross 140W and move into the central
Pacific basin by early Monday morning, then approach the Hawaiian
Islands on Tuesday and Wednesday.


KEY MESSAGES:

1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands early next week. It is too early to
determine the exact location and magnitude of potential impacts
given uncertainties in the track, intensity, and structure of Calvin
as it approaches the islands. Interests in Hawaii should closely
monitor the latest forecast updates.


FORECAST POSITIONS AND MAX WINDS

INIT 15/0300Z 14.2N 126.0W 105 KT 120 MPH
12H 15/1200Z 14.6N 128.2W 100 KT 115 MPH
24H 16/0000Z 15.3N 131.1W 90 KT 105 MPH
36H 16/1200Z 16.0N 134.1W 75 KT 85 MPH
48H 17/0000Z 16.6N 137.0W 65 KT 75 MPH
60H 17/1200Z 17.1N 140.1W 55 KT 65 MPH
72H 18/0000Z 17.5N 143.7W 45 KT 50 MPH
96H 19/0000Z 18.5N 150.5W 35 KT 40 MPH
120H 20/0000Z 19.5N 157.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven

[Yellow Evan]

Definitely more receptive to the SST gradient than I thought. As a result, it is getting harder to imagine this retaining convection over 23-24C SSTs.

[Kingarabian]

That southerly shear is doing a lot of damage.

[cycloneye]

Hurricane Calvin Discussion Number 15
NWS National Hurricane Center Miami FL EP032023
1100 PM HST Fri Jul 14 2023

This evening's satellite and microwave presentation reveals a
significantly degraded cloud pattern. A recent SSMI/S image
indicated inner core erosion in the southeast quadrant and no
apparent outer ring development. Calvin's eye has become obscured
and has cooled (-27C), and the GFS model sounding indicated that
there could be some southeasterly shear undercutting the upper-level
diffluent flow. The subjective intensity estimates from both TAFB
and SAB yield 90 kt, the UW-CMISS objective ADT and AiDT intensity
estimates are 87 and 88 kt, respectively. Additionally, a RADARSAT
(RCM 2) SAR overpass estimated maximum sustained winds of 88-93 kt.
Based on these data, the initial intensity is lowered to 90 kt for
this advisory.

Even though minor intensity fluctuations are possible in the
short term, Calvin should continue to spin down as the cyclone
traverses cooler waters Saturday while moving into a more
stable drier air mass. The statistical-dynamical SHIPS models
agree that increasing southwesterly vertical shear should also be
an inhibiting factor by 96 hours. Global model simulated
infrared satellite imagery continues to show Calvin losing its
organized convection early next week and the NHC forecast calls for
the cyclone to degenerate to a post-tropical remnant low by day 5,
if not sooner. The intensity forecast indicates a faster
rate of weakening through day 3 than the previous forecast, and
closely follows the HCCA, IVCN, and LGEM intensity models, and is
just below the Decay SHIPS.

The initial motion is estimated to be west-northwestward, or 285/14
kt. There is no change to the forecast philosophy. The hurricane
is expected to move within the deep east-southeasterly steering flow
produced by a subtropical ridge stretching across the eastern
Pacific through the period. There continues to be quite a bit of
uncertainty, with Calvin either passing near or over the Hawaiian
Islands. The global models have been trending poleward, either over
or just to the north of the Big Island while along-track
inconsistencies remain. The most reasonable forecast approach is to
hedge toward the best performing consensus aids HCCA and TVCE, and
the official track forecast is based on this reliable method.
Calvin is still expected to cross 140W and move into the central
Pacific basin by early Monday morning, then approach the Hawaiian
Islands on Tuesday and Wednesday.

Calvin's wind radii have been adjusted based on a RADARSAT (RCM 2)
15Jul 0245 UTC overpass.


KEY MESSAGES:

1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands early next week. It is too early to
determine the exact location and magnitude of potential impacts
given uncertainties in the track, intensity, and structure of Calvin
as it approaches the islands. Interests in Hawaii should closely
monitor the latest forecast updates.


FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 14.5N 127.5W 90 KT 105 MPH
12H 15/1800Z 15.0N 129.7W 80 KT 90 MPH
24H 16/0600Z 15.7N 132.6W 70 KT 80 MPH
36H 16/1800Z 16.4N 135.5W 60 KT 70 MPH
48H 17/0600Z 17.0N 138.6W 55 KT 65 MPH
60H 17/1800Z 17.5N 142.0W 45 KT 50 MPH
72H 18/0600Z 18.1N 145.5W 40 KT 45 MPH
96H 19/0600Z 19.1N 152.7W 35 KT 40 MPH
120H 20/0600Z 20.5N 159.6W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Roberts

[Yellow Evan]

Confused why the NHC is using SAR given it's erratic history and horrid RMSE.

[Yellow Evan]

 https://twitter.com/cyanide_bot/status/1680198793193742341




 https://twitter.com/cyanide_bot/status/1680198793789337600

[Yellow Evan]

Annular. Calvin would probably be T5.5 now had it not collapsed its core yesterday during D-Min.

[Sciencerocks]

[Kingarabian]

https://media.discordapp.net/attachments/857017650042503178/1129761200528441454/IMG_8278.png

Annular. Calvin would probably be T5.5 now had it not collapsed its core yesterday during D-Min.

Some characteristics and it is trying to transition but too much banding on IR for it to be an annular. Imagine on MW.

[Kingarabian]

Confused why the NHC is using SAR given it's erratic history and horrid RMSE.

Agreed.

[cycloneye]

Hurricane Calvin Discussion Number 16
NWS National Hurricane Center Miami FL EP032023
500 AM HST Sat Jul 15 2023

The ragged eye of Calvin has been apparent at times in conventional
satellite imagery this morning, but overall it has become less
defined. Overnight GMI and more recent SSMIS passive microwave data
show that some deep convection has eroded within the eastern portion
of the eyewall. The vortex also appears somewhat tilted with height,
as the 37 GHz low-level center was displaced a bit to the south of
the 89 GHz mid-level one. A blend of the latest objective UW-CIMSS
satellite estimates and subjective Dvorak classifications from TAFB
and SAB support an initial intensity of 85 kt.

The weakening trend that began last night is expected to continue
for the next several days due to Calvin moving over cooler waters
and into a drier and more stable environment. Also, southwesterly
deep-layer shear is forecast to increase from 60-120 h as the
cyclone traverses the central Pacific. This will adversely affect
its ability to sustain organized convection, although to what extent
is still somewhat uncertain. Regardless of its tropical or
post-tropical status, Calvin appears likely to maintain some
tropical-storm-force winds in the northern portion of its
circulation through 96 h. Overall, few changes were made to the
updated NHC intensity forecast, which closely follows the
multi-model HCCA and IVCN aids. The global model fields suggest the
system could open up into a trough soon after day 5.

Calvin is moving quickly west-northwestward at 285/14 kt. With a
well-established mid-level ridge over the eastern Pacific, this
general motion is expected to continue through the forecast period.
This course brings Calvin into the central Pacific basin (west of
140W) by Monday morning and toward the Hawaiian Islands on Tuesday
and Wednesday. The guidance is reasonably well clustered on a track
near or over the Big Island of Hawaii, but any potential impacts
will be dictated by the track details that are still quite
uncertain at this time. The updated NHC track forecast is a bit
faster and slightly south of the previous one at days 3-5, in
agreement with the latest consensus aids and near the center of the
guidance envelope.


KEY MESSAGES:

1. Calvin is forecast to move across the central Pacific Ocean and
approach the Hawaiian Islands early next week. It is too early to
determine the exact location and magnitude of potential impacts
given uncertainties in the track, intensity, and structure of Calvin
as it approaches the islands. Interests in Hawaii should closely
monitor the latest forecast updates.


FORECAST POSITIONS AND MAX WINDS

INIT 15/1500Z 14.7N 129.0W 85 KT 100 MPH
12H 16/0000Z 15.3N 131.1W 80 KT 90 MPH
24H 16/1200Z 16.0N 134.1W 70 KT 80 MPH
36H 17/0000Z 16.6N 137.1W 60 KT 70 MPH
48H 17/1200Z 17.1N 140.5W 55 KT 65 MPH
60H 18/0000Z 17.6N 144.0W 50 KT 60 MPH
72H 18/1200Z 18.1N 147.6W 45 KT 50 MPH
96H 19/1200Z 19.1N 154.9W 35 KT 40 MPH
120H 20/1200Z 20.5N 161.5W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Reinhart

[Yellow Evan]

[Kingarabian]

Impacts will be mainly heavy rainfall and potential flooding, especially Hilo side. Fortunately it will move in and out quick.