EPAC: GILMA - Post-Tropical - Discussion

[InfernoFlameCat]

They going with 110 knots. Sigh. Not that it really matters but it really was more intense than that imo.

[Kingarabian]

First time I ever see the NHC go below an unanmious estimate from SAB-TAFB-ADT. They all supported 115kts yet they somehow went with 110kt. Hate to say it but a lot of JTWC/IMD energy going on with this system.

[cycloneye]

Hurricane Gilma Discussion Number 28
NWS National Hurricane Center Miami FL EP072024
500 PM HST Sat Aug 24 2024

Gilma continues to defy the odds and intensify. The satellite
depiction over the last several hours has been one of a
well-organized strengthening hurricane. The eyewall is tightly
wrapped producing deep convection with lightning depicted in the
northern eyewall on GLM satellite imagery. Visible imagery shows
that the eye has become circular, well-defined, and has been
clearing out. Subjective Dvorak estimates have increased but were
constrained to T6.0/115 kt from both SAB and TAFB, with both
agencies reporting higher data-T values. Objective satellite
intensity estimates from UW-CIMSS range from 105-115 kt. Using a
blend of these estimates the initial intensity is raised to 110 kt
for this advisory. Therefore, Gilma's strengthening has met the
definition of rapid intensification as the system has strengthened
30 kt in 12 h.

The initial motion remains 275/8 kt. A mid-level ridge to the
north of the hurricane continues to gradually build and strengthen.
This should steer Gilma on a generally westward track through the
forecast period. Model guidance is in fairly good agreement,
although there continues to be some forward speed differences,
particularly towards the end of the period. The NHC forecast is
very similar to the previous advisory.

Gilma has managed to rapidly intensify over marginally warm sea
surface temperatures, and has established a well-defined inner
core within a very low wind shear environment. The system's
slightly increasing forward speed may have also allowed it to avoid
some of the negative impacts from upwelling. Given the higher
initial intensity there are some changes in the near-term
intensity forecast, with Gilma maintaining hurricane strength longer
than previously forecast. As Gilma moves into cooler SSTs and a
little more wind shear, this will cause a gradual weakening trend to
ensue. Beyond 24 h the system will begin to move into a drier and
more stable airmass which should increase the rate of weakening as
wind shear further increases by days 3-4. Global models show Gilma
starting to struggle to produce convection around day 5, with the
NHC forecast depicting Gilma as a remnant low at that time. The NHC
forecast is above most of the intensity guidance in the near term
given the higher initial intensity, but is near the simple consensus
intensity aids as the system begins to weaken.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 17.8N 131.8W 110 KT 125 MPH
12H 25/1200Z 17.9N 133.1W 110 KT 125 MPH
24H 26/0000Z 18.1N 134.9W 100 KT 115 MPH
36H 26/1200Z 18.3N 136.6W 90 KT 105 MPH
48H 27/0000Z 18.5N 138.5W 80 KT 90 MPH
60H 27/1200Z 18.7N 140.4W 70 KT 80 MPH
72H 28/0000Z 18.9N 142.4W 60 KT 70 MPH
96H 29/0000Z 19.6N 146.5W 45 KT 50 MPH
120H 30/0000Z 20.3N 150.8W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kelly

[Yellow Evan]

SATCON at 105 is probably holding the NHC down as well as that ADT/AiDT were not 115 at the time of preparing the advisory.

[Kingarabian]

:uarrow: SATCON at 105 is probably holding the NHC down as well as that ADT/AiDT were not 115 at the time of preparing the advisory.

SATCON seems to be used sporadically. ADT CI was up to 5.8 like an hour before the advisory. Blend still supported 115kts.

I mean it doesn't matter but looks like they're more conservative than normal in the EPAC this past week.

[Yellow Evan]

EP, 07, 2024082506, , BEST, 0, 179N, 1321W, 115, 949, HU, 64, NEQ, 20, 20, 15, 20, 1011, 240, 15, 0, 0, E, 0, , 0, 0, GILMA, D, 0, , 0, 0, 0, 0, genesis-num, 018,

[aspen]

First time I ever see the NHC go below an unanmious estimate from SAB-TAFB-ADT. They all supported 115kts yet they somehow went with 110kt. Hate to say it but a lot of JTWC/IMD energy going on with this system.

Yup. Even down to the fact that they operationally assessed its peak intensity after it’s already been weakening, like Bualoi ‘19 and others (5am finally upgraded it to a minimal Cat 4).

Out of all the likely under-estimated Cat 4s between 120-140W over the last several years (Douglas, Felicia, Darby, and Dora), Gilma is easily the most egregious. Even accounting for poor satellite estimates, the NHC was far too conservative. At least it’s not an under-estimated system threatening land.

[cycloneye]

Hurricane Gilma Discussion Number 29
NWS National Hurricane Center Miami FL EP072024
1100 PM HST Sat Aug 24 2024

After a brief period of rapid strengthening earlier this evening,
Gilma's intensity has leveled off. Conventional GOES-18 satellite
imagery shows that the deep inner core convection has eroded
considerably in the western half of the cyclone. The initial
intensity is set at 115 kt and is based on a blend of the
subjective Dvorak intensity estimates and various UW-CIMSS
objective techniques. Although the current intensity is higher
than noted in the previous advisory, Gilma likely peaked a few
hours ago based on earlier ADT intensity estimates of 115-119 kt
and the 0000 UTC constrained Data-T 6.5 subjective estimates from
both TAFB and SAB.

Although Gilma's period of rapid intensification has likely ended,
some intensity fluctuations, common in major hurricanes, are
possible in the short term, and the official forecast indicates
little intensity change through Sunday. Afterward, the cyclone is
expected to traverse cooler oceanic surface temperatures and move
into a thermodynamically inhibiting dry and stable marine layer by
the middle-part of the forecast. Early next week, the statistical
SHIPS intensity guidance shows an increase in west-southwesterly
shear spreading east of the Big Island of Hawaii. These negative
intensity contributions should result in a weakening trend through
the remainder of the forecast period. The NHC intensity forecast
has been nudged upward slightly from the previous one and is based
on a blend of the Decay SHIPS statistical aid and the IVCN consensus
model.

Gilma's initial motion is estimated to be west-northwestward, or
285/8 kt. A strengthening mid-troposphere subtropical ridge
situated to the north of the hurricane should steer Gilma on a
generally west-northwest or west track through day 5. The official
track forecast is a little bit slower than the previous advisory
beyond day 3 and is a compromise of the HCCA and TVCE consensus
guidance.

Gilma's wind radii have been adjusted based on a 0530 UTC METOP-B
ASCAT overpass.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 18.0N 132.5W 115 KT 130 MPH
12H 25/1800Z 18.1N 133.8W 115 KT 130 MPH
24H 26/0600Z 18.3N 135.5W 100 KT 115 MPH
36H 26/1800Z 18.5N 137.3W 85 KT 100 MPH
48H 27/0600Z 18.7N 139.1W 75 KT 85 MPH
60H 27/1800Z 18.9N 141.0W 65 KT 75 MPH
72H 28/0600Z 19.2N 142.8W 55 KT 65 MPH
96H 29/0600Z 20.0N 146.6W 40 KT 45 MPH
120H 30/0600Z 20.6N 150.1W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Roberts

[cycloneye]

Hurricane Gilma Discussion Number 31
NWS National Hurricane Center Miami FL EP072024
1100 AM HST Sun Aug 25 2024

GOES-18 satellite images indicate that Gilma's eye continues to
become more cloud-filled and less well-defined. Microwave images
from earlier this morning showed a better-defined eye at that time.
The latest subjective intensity estimates from TAFB and SAB are
T-5.5/102 kt. The UW-CIMSS objective intensity estimates have also
decreased from 6 hours ago, and range from about 77 to 104 kt. The
initial intensity has been lowered to 100 kt for this advisory,
based on a blend of the data.

A combination of dry environmental air and marginal SSTs are likely
the reasons why Gilma has weakened some today. Gilma should
continue to move over SSTs near or just above 26C for another 24 h
before it reaches slightly cooler waters. Gilma is still located
within an environment of low vertical wind shear but is forecast to
move into 15 kt of westerly vertical wind shear by early Monday
which is expected to cause the storm to weaken. The new NHC
intensity forecast is similar to the previous forecast and
is very near the intensity consensus aids. The forecast shows
steady weakening by about 15 kt per day. By day 4, Gilma should
move into an area of moderate to strong west-southwesterly vertical
wind shear, which should strip away any remaining convection.
Therefore, the forecast calls for Gilma to become a remnant low by
day 5.

Gilma has been moving due west over the past 12 h, or 270/9 kt. A
mid-tropospheric ridge should continue to steer Gilma between west
and west-northwest for the next several days. The NHC track
forecast is nearly on top of the previous prediction and is close
to a blend of the HCCA and TVCE consensus aids through 72 h. The
NHC forecast is slightly south of those consensus aids beyond 72 h.


FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 18.0N 134.3W 100 KT 115 MPH
12H 26/0600Z 18.1N 135.7W 90 KT 105 MPH
24H 26/1800Z 18.3N 137.4W 85 KT 100 MPH
36H 27/0600Z 18.5N 139.1W 75 KT 85 MPH
48H 27/1800Z 18.7N 140.9W 70 KT 80 MPH
60H 28/0600Z 19.0N 142.7W 60 KT 70 MPH
72H 28/1800Z 19.4N 144.5W 55 KT 65 MPH
96H 29/1800Z 20.0N 147.9W 40 KT 45 MPH
120H 30/1800Z 20.6N 152.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Hagen/Pasch

[cycloneye]

Hurricane Gilma Discussion Number 32
NWS National Hurricane Center Miami FL EP072024
500 PM HST Sun Aug 25 2024

Gilma is a compact hurricane with a small eye noted in both
infrared satellite imagery and a recent 0039 UTC SSMIS microwave
overpass. The microwave imagery showed that the convection
associated with Gilma has eroded over the southern semicircle,
likely due to an increase in shear and dry air intrusion. The
initial intensity has been lowered to 90 kt, which is a blend of
the latest objective and subjective intensity estimates. It should
be noted that the range of the satellite intensity estimates is
atypically large and is around 75 kt on the low side to around
100 kt at the upper end.

Westerly shear over Gilma is forecast to increase to moderate
levels during the next 24 hours, and this along with nearby dry
mid-level air and slightly lower SSTs are expected to cause gradual
weakening during the next couple of days. Around 72 hours a more
substantial increase in vertical wind shear is anticipated and this
should result in a faster rate of weakening. The global models
suggest the system is likely to struggle to produce organized
deep convection by day 4, and Gilma is forecast to become a
post-tropical cyclone around that time.

Gilma has been moving just north of due west (275/8 kt) during the
past 12 hours. A mid-level ridge to the north of Gilma should
continue to steer the storm on a westward to west-northwestward
heading throughout much of this week. The track guidance is in
good agreement during the next 48-72 hours, but there is greater
spread in Gilma's forward speed at days 4 and 5. This is related
to how long Gilma remains vertically coherent. The models that
weaken the cyclone more quickly favor a faster forward speed later
in the forecast period. The NHC track forecast is a little faster
at 96 and 120 h to be closer to the latest consensus aids.
Otherwise, the new track forecast is essentially an update of
the previous official forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 18.1N 135.1W 90 KT 105 MPH
12H 26/1200Z 18.2N 136.4W 85 KT 100 MPH
24H 27/0000Z 18.4N 138.1W 75 KT 85 MPH
36H 27/1200Z 18.6N 139.8W 70 KT 80 MPH
48H 28/0000Z 18.9N 141.8W 65 KT 75 MPH
60H 28/1200Z 19.2N 143.7W 55 KT 65 MPH
72H 29/0000Z 19.6N 145.5W 50 KT 60 MPH
96H 30/0000Z 20.3N 149.3W 35 KT 40 MPH...POST-TROPICAL
120H 31/0000Z 21.1N 153.6W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown

[Hurricane2022]

? ? ?

[ElectricStorm]

Trying to clear an eye out again. This storm refuses to quit

[cycloneye]

Hurricane Gilma Discussion Number 33
NWS National Hurricane Center Miami FL EP072024
1100 PM HST Sun Aug 25 2024

This evening's satellite presentation consists of a ragged
partially obscured eye with a small inner core open in the south
semi-circle. Gilma's cloud pattern continues to deteriorate slowly
and has shed most of the associated convective bands with the
exception of fragmented curved band wrapping in from the south.
The initial intensity is lowered to 85 kt and is based on the
Dvorak satellite intensity estimates from TAFB and SAB and a blend
of the UW-CIMSS ADT, AiDT, and DMINT objective estimates, yielding
83 kt.

Water vapor imagery and global model RH/700mb fields indicate that
the cyclone is moving toward a dry, stable air mass, indicative of
a large low-level stratocumulus cloud deck intruding from the
northwest in the GOES-18 Proxy-VIS images. Subsequently, the
statistical GFS/ECMWF SHIPS indicated a mid-level/700-500mb RH of
42 percent. This inhibiting thermodynamic contribution, along with
increasing west-to-west-southwesterly shear noted in the
statistical SHIPS intensity guidance, particularly beyond 36 hrs,
should cause Gilma to weaken at a quicker rate through day 5.
The NHC intensity forecast is a compromise of the Decay-SHIPS and
the IVCN intensity consensus and shows Gilma degenerating to a
post-tropical cyclone in 4 days.

Gilma's initial motion is estimated to be westward, or 280/8 kt,
and is moving in the southern periphery of a mid-tropospheric
subtropical ridge extending westward across the tropical-eastern
Pacific from northwestern Mexico. The global and regional models
are fairly clustered together and indicate a slightly to the right
of the initial track motion, or west-northwestward beyond the 60 hr
period, and the official forecast follows suit. Along-track
differences continue to be a model inconsistency, but following the
skilled TVCE and HCCA consensus models have been the best track
forecast solution so far.

Gilma's 50 kt wind radii have been slightly adjusted based on a
0559 UTC METOP-C ASCAT overpass.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 18.1N 135.9W 85 KT 100 MPH
12H 26/1800Z 18.3N 137.1W 80 KT 90 MPH
24H 27/0600Z 18.5N 138.9W 70 KT 80 MPH
36H 27/1800Z 18.7N 140.9W 65 KT 75 MPH
48H 28/0600Z 19.0N 143.0W 60 KT 70 MPH
60H 28/1800Z 19.4N 145.0W 50 KT 60 MPH
72H 29/0600Z 19.8N 147.0W 45 KT 50 MPH
96H 30/0600Z 20.6N 151.0W 35 KT 40 MPH...POST-TROPICAL
120H 31/0600Z 21.6N 155.7W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Roberts

[cycloneye]

Still looks good with that eye.

[Hurricane2022]

What the hellllllllllllllllll

[cycloneye]

Hurricane Gilma Discussion Number 34
NWS National Hurricane Center Miami FL EP072024
500 AM HST Mon Aug 26 2024

Gilma still has a well-defined eye, seen on GOES-18 infrared and
proxy-vis satellite imagery. The latest subjective intensity
estimates are T-4.5/77 kt from TAFB and T-5.0/90 kt from SAB. Recent
objective intensity estimates from UW-CIMSS such as the ADT and
DPRINT are in the 80 to 85 kt range. However, during the last
couple of hours, the eye has warmed and the cloud tops in the
eyewall have cooled, so the initial intensity is increased to 90 kt,
in best agreement with the SAB Dvorak intensity estimate.

Gilma is likely currently experiencing 10 to 15 kt of westerly wind
shear as it continues moving near and parallel to the 26C SST
isotherm. Fluctuations in intensity appear possible for the next 12
h. Beyond 12 to 18 h, the westerly shear is forecast to increase to
the 15 to 20 kt range, and the SSTs are forecast to decrease
slightly along the path beyond 36 h. These factors, along with the
relatively dry, stable environmental air mass that Gilma will be
traversing for the remainder of its lifetime, are expected to lead
to continued steady weakening. The NHC intensity forecast is a bit
higher than the previous official forecast at hour 12, and then is
similar to the previous official forecast. The NHC forecast is near
the middle of the intensity guidance envelope.

Gilma's initial motion is estimated to be westward, or 275/7 kt as
it continues moving along the southern periphery of a
mid-tropospheric subtropical ridge. The models continue to be in
good cross-track agreement that the west to west-northwestward
motion will continue, although there are still some along-track
differences in the guidance. The new NHC forecast lies very close
to, but perhaps a touch to the south of the previous official
forecast. This forecast is close to the HCCA and TCVE consensus
aids.


FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 18.2N 136.5W 90 KT 105 MPH
12H 27/0000Z 18.3N 137.9W 85 KT 100 MPH
24H 27/1200Z 18.5N 139.8W 70 KT 80 MPH
36H 28/0000Z 18.7N 141.9W 60 KT 70 MPH
48H 28/1200Z 19.0N 144.0W 55 KT 65 MPH
60H 29/0000Z 19.5N 146.0W 45 KT 50 MPH
72H 29/1200Z 19.9N 148.0W 40 KT 45 MPH
96H 30/1200Z 20.8N 152.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 31/1200Z 21.8N 156.9W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Hagen/Pasch

[aspen]

Man Gilma won’t give up. It’s impressive how well it’s been holding despite being stuck over marginal SSTs for days, in a location where you’d expect it to not fare well given that it’s a La Niña year.

It probably won’t get the EPac’s ACE to match the Atlantic’s but A for effort.

[Teban54]

Is Gilma still intensifying???

[Kingarabian]

Is Gilma still intensifying???

https://i.postimg.cc/2jFPzB8h/goes18-ir-07-E-202408261125.gif

If Eye temp becomes positive, it's an automatic Cat.3 on Dvorak since the CDO is cold enough and there is no constraints.

[Kingarabian]

RAW and ADJ numbers from ADT are at 5.1. B ring is almost connected. Should be a 5.5 soon.