EPAC: GILMA - Post-Tropical - Discussion

[Kingarabian]

Big implications if this continues to go south of track.

It'll have more time over warmer waters and could lead it getting closer to the islands than currently modeled.

[Yellow Evan]

[cycloneye]

Hurricane Gilma Discussion Number 14
NWS National Hurricane Center Miami FL EP072024
200 PM PDT Wed Aug 21 2024

Gilma's satellite presentation has improved significantly over the
past three hours as a clear eye has appeared in visible imagery, and
the latest subjective Dvorak intensity estimates from TAFB and SAB
were both T5.0/90-kt. Using these estimates Gilma's initial
intensity is set to 90 kt for this advisory, which represents an
increase of 30-kt over the past 24 hours, meeting the criteria of
rapid intensification.

Gilma is moving more west-northwestward this afternoon, estimated at
285/6 kt. Over the next few days, a large subtropical ridge poleward
of the hurricane should continue to steer it generally westward to
west-northwestward. The latest track guidance has shifted slightly
poleward, reversing the trend of the previous few cycles, possibly
due to the more northern short-term motion as the hurricane's
inner-core has become established. The latest NHC track was shifted
slightly in that direction of the consensus track aids, blending
them with the prior track forecast.

Given the improvements to the inner core, Gilma is expected to
steadily strengthen over the next day. The NHC intensity forecast
now shows strengthening to a Category 4 hurricane in 24 h, which is
in agreement with the latest HCCA consensus aid and still slightly
below some of the hurricane-regional models (e.g. HAFS-A and
HAFS-B). After 48 h, sea-surface temperatures begin to gradually
decrease, and slow weakening is still expected to begin at that
time, though a little less than the previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 16.3N 123.2W 90 KT 105 MPH
12H 22/0600Z 16.6N 124.0W 105 KT 120 MPH
24H 22/1800Z 16.9N 125.2W 115 KT 130 MPH
36H 23/0600Z 17.1N 126.4W 110 KT 125 MPH
48H 23/1800Z 17.4N 127.8W 105 KT 120 MPH
60H 24/0600Z 17.6N 129.3W 100 KT 115 MPH
72H 24/1800Z 17.7N 131.0W 95 KT 110 MPH
96H 25/1800Z 18.0N 134.6W 85 KT 100 MPH
120H 26/1800Z 18.5N 138.6W 75 KT 85 MPH

$$
Forecaster Alaka/Papin

[lilbump3000]

https://www.youtube.com/@w.o.f.weathero ... irmation=1

[Kingarabian]

18z GFS came in with much more shear in the CPAC than the rest of the models.

Currently under 15kts of mid level shear. Looks like it will drop below 10kts by tomorrow.

[Kingarabian]

Latest BD images are a steady 5.5.



Core needs to moisten up.

[cycloneye]

EP, 07, 2024082200, , BEST, 0, 164N, 1235W, 95, 968, HU

[cycloneye]

Hurricane Gilma Discussion Number 15
NWS National Hurricane Center Miami FL EP072024
800 PM PDT Wed Aug 21 2024

Infrared and visible satellite imagery of Gilma this evening
continues to depict a strong inner core with a well-defined eye.
Deep convection with cold cloud tops near -80C have been persistent
in the southern eye wall. Over the last hour or so the northern
portion of the inner core has become a little more broken in
infrared imagery, which suggests the rapid intensification has
stopped. Subjective Dvorak satellite intensity estimates for this
cycle remained unchanged from TAFB and SAB, both T5.0/90-kt. The
objective intensity estimates from UW-CIMSS range from 90 to 100
kt. Using a blend of theses estimates, Gilma's initial intensity is
set to 95 kt for this advisory.

Gilma is moving slowly west-northwestward with an estimated motion
of 290/6 kt. A large subtropical ridge will continue to steer Gilma
generally westward to west-northwestward during the next few days,
with a gradual acceleration by the weekend. The latest NHC track is
slightly to the right of the previous forecast, and lies between
the previous forecast and the latest consensus aids.

Gilma is expected to continue to strengthen over the next day or so
as the system moves over warm sea surface temperature with low
vertical wind shear. The main change this cycle is that the peak and
entire forecast period intensity guidance is much lower compared to
6 hours ago. The NHC peak intensity forecast is slightly lower than
previous but still shows steady strengthening over the next 24h.
However, the system should then begin to traverse cooler waters and
a drier more stable airmass, with a faster weakening trend compared
to the previous advisory. Note that the NHC intensity forecast is
above most of the intensity guidance, primarily due to continuity
constraints, and additional changes in the intensity forecast may be
needed in subsequent forecasts if intensity aid trends continue.

FORECAST POSITIONS AND MAX WINDS

INIT 22/0300Z 16.5N 123.8W 95 KT 110 MPH
12H 22/1200Z 16.8N 124.7W 105 KT 120 MPH
24H 23/0000Z 17.1N 125.9W 110 KT 125 MPH
36H 23/1200Z 17.3N 127.2W 100 KT 115 MPH
48H 24/0000Z 17.5N 128.7W 95 KT 110 MPH
60H 24/1200Z 17.8N 130.4W 90 KT 105 MPH
72H 25/0000Z 18.0N 132.2W 85 KT 100 MPH
96H 26/0000Z 18.5N 135.9W 75 KT 85 MPH
120H 27/0000Z 19.1N 140.0W 65 KT 75 MPH

$$
Forecaster Kelly

[lilbump3000]

https://www.youtube.com/@w.o.f.weathero ... irmation=1

[Yellow Evan]

Losing bands and becoming more symmetrical. Annular transition likely overnight.

[Kingarabian]

18z and 00z GFS runs pretty much think this has peaked.

[ElectricStorm]

Probably a major now based on ADT

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

----- Current Analysis -----
Date : 22 AUG 2024 Time : 044020 UTC
Lat : 16:28:47 N Lon : 123:48:00 W


CI# /Pressure/ Vmax
5.5 / 959.9mb/102.0kt


Final T# Adj T# Raw T#
5.5 5.7 5.7

Estimated radius of max. wind based on IR : 22 km

Center Temp : +10.9C Cloud Region Temp : -60.2C

Scene Type : EYE

[Kingarabian]

B ring almost wrapping around completely. Should be an automatic 6.0 if it does.

[Yellow Evan]

Downshear convective burst wrapping around. Shear spikes visible, meaning the storm is fighting back against moderate shear.

[Yellow Evan]

EP, 07, 2024082206, , BEST, 0, 165N, 1239W, 100, 963, HU, 64, NEQ, 25, 25, 10, 15, 1013, 230, 10, 0, 0, E, 0, , 0, 0, GILMA, D, 0, , 0, 0, 0, 0, genesis-num, 018,

[cycloneye]

Hurricane Gilma Discussion Number 16
NWS National Hurricane Center Miami FL EP072024
200 AM PDT Thu Aug 22 2024

Gilma has continued to intensify while exhibiting a well-defined
eye on geostationary satellite imagery, and convective cloud tops
colder than -70 deg C are evident around the eyewall. The cloud
pattern is fairly symmetric in appearance, and upper-level outflow
is well defined over all quadrants of the circulation. The current
intensity estimate is raised to 100 kt based on a subjective Dvorak
classification from TAFB and various objective estimates from
UW-CIMSS. This makes Gilma the first major hurricane of the 2024
east Pacific season.

Center fixes show a fairly slow forward speed toward the
west-northwest, with an initial motion estimate of 290/5 kt. A
mid-tropospheric trough near the California coast has broken down
the subtropical ridge to the north of Gilma, resulting in a weaker
than normal steering current. Over the next several days, the ridge
is expected to build back rather slowly, resulting in only a gradual
increase in the tropical cyclone's forward speed over the forecast
period. The official track forecast is about the same as the one
from the previous NHC advisory, and is near the southern side of the
model suite.

Some additional strengthening is expected, since the system has a
well-defined inner core and is in an environment of low shear while
situated over warm waters. The short-term intensity forecast
reflects current trends and is in line with much of the regional
dynamical hurricane model guidance. In the next day or two, the
SSTs below Gilma are expected to gradually decrease. Later in the
forecast period, the cyclone will be moving into a drier and more
stable air mass. These factors should cause slow weakening, and the
official intensity forecast is similar to the previous one.
Overall, the NHC intensity forecast is on the high end of the model
guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0900Z 16.6N 124.2W 100 KT 115 MPH
12H 22/1800Z 16.9N 125.0W 110 KT 125 MPH
24H 23/0600Z 17.2N 126.3W 105 KT 120 MPH
36H 23/1800Z 17.5N 127.7W 95 KT 110 MPH
48H 24/0600Z 17.8N 129.3W 90 KT 105 MPH
60H 24/1800Z 18.0N 131.0W 85 KT 100 MPH
72H 25/0600Z 18.3N 132.6W 80 KT 90 MPH
96H 26/0600Z 18.6N 136.0W 70 KT 80 MPH
120H 27/0600Z 19.0N 140.0W 60 KT 70 MPH

$$
Forecaster Pasch

[Hurricane2022]

This is eye candy for me. I even forget that she has a name when I stop to observe

[aspen]

The NHC estimate is probably 5-10 kt too low, but I’m not sure its satellite presentation quite justified a Cat 4 yet. Still, this seems like it’ll once again be incredibly difficult for ADT to give a good intensity estimate with the fairly warm CDO.

[cycloneye]

Hurricane Gilma Discussion Number 17
NWS National Hurricane Center Miami FL EP072024
Issued by the NWS Weather Prediction Center College Park MD
500 AM HST Thu Aug 22 2024

Gilma has continued to intensify with recent tightening of the
eyewall diameter in the last few hours. Concurrently, solid cooling
was noted in the surrounding inner ring of convection. This
has resulted in an increase in intensity for the Dvorak intensity
estimates with TAFB up to a T6.0/6.0 or 115 knots while
objective estimates from UW-CIMSS has seen a variation of Raw-T
values between 5.5 and 5.8. As such, the intensity has been
adjusted slightly upward to 110 knots and brings intensity up to
a strong Category 3 hurricane on the Saffir-Simpson Scale.

A northwest trend in center fixes continues to show slow forward
speed at 290/6 knots, though small wobbles have been noted as the
eye has been tightening and stronger convergence nodes are noted
along the inner eye wall supporting a weak asymmetry to the eye
itself. Given weak mid-tropospheric forcing, storm motion will
continue to be slow and is expected to turn more westward Friday
into Saturday as it nears the 26-27C isotherm. Proximity to the
thermal gradient and convective activity will play a role in the
longer term forecast as well. Depending on the strength, a faster
forward speed was noted through the guidance suite. As such, the
official forecast is a bit faster along track though the track
remains fairly stable.

Given that warmer oceans remain along the track of Gilma, some
additional strengthening is expected with the low shear
environment. As the cyclone reaches the 26-27C isotherm, gradual
weakening is expected, but a slight northward adjustment will
result in reduced warm, moist air to maintain its strength and
slow weakening is expected after Friday morning. As the storm
treads further west, cooler water is likely to increase weakening of
the system through the weekend into early next week. As the system
weakens and becomes shallower, forward speed will increase and
perhaps further compound the weakening process a bit faster than
prior forecast; however, the NHC intensity forecast
remains on the higher end of the model guidance suite to better
maintain continuity.


FORECAST POSITIONS AND MAX WINDS

INIT 22/1500Z 16.9N 124.5W 110 KT 125 MPH
12H 23/0000Z 17.1N 125.4W 115 KT 130 MPH
24H 23/1200Z 17.5N 126.8W 105 KT 120 MPH
36H 24/0000Z 17.8N 128.3W 100 KT 115 MPH
48H 24/1200Z 18.1N 129.9W 95 KT 110 MPH
60H 25/0000Z 18.3N 131.5W 90 KT 105 MPH
72H 25/1200Z 18.4N 133.3W 80 KT 90 MPH
96H 26/1200Z 18.8N 137.1W 65 KT 75 MPH
120H 27/1200Z 19.1N 141.3W 55 KT 65 MPH

$$
Forecaster Gallina

[HurricaneRyan]

Gilman will likely be the storm of the season for the EPAC