EPAC: GILMA - Post-Tropical - Discussion

[Kingarabian]

GFS backing off on intensity. Looks a little bit better today but the LLC is still exposed to the NE of the convection.

[DorkyMcDorkface]

GFS backing off on intensity. Looks a little bit better today but the LLC is still exposed to the NE of the convection.

GFS has this weird sloppy double-lobed thing going on, almost like a binary interaction. That's probably why it's more bearish all of a sudden.

[Kingarabian]

GFS backing off on intensity. Looks a little bit better today but the LLC is still exposed to the NE of the convection.

GFS has this weird sloppy double-lobed thing going on, almost like a binary interaction. That's probably why it's more bearish all of a sudden.https://i.ibb.co/djqDCTh/gfs-z850-vort-epac-fh24-78.gif

12z GFS back to being more bullish.

Still hard to see it get much stronger than a minimal hurricane if it takes a NW path too soon. ICON has it on a more WNW track though.

[DorkyMcDorkface]

*weenie mode on*
Oh please make it happen
*weenie mode off*

[ElectricStorm]

07E GILMA 240819 1800 15.0N 116.5W EPAC 50 999

[aspen]

*weenie mode on*
Oh please make it happen
*weenie mode off*
https://i.ibb.co/DrGN99M/hafsa-sat-IR-07-E-40.png

Basically all the hurricane models show it, so yeah the odds for it going annular seem good.

[Kingarabian]

Finally getting some convection over the center. Just need the easterly shear to come down a bit.

[Yellow Evan]

GFS has an excellent 200 mbar pattern, although the mid-level weakness will ensure there's some shear.



ECMWF is unsurprisingly more conservative, with shear never dipping below ~15 knots on the 12z run before increasing in about 4-5 days. This also reaches the 26C isotherm if this goes above ~19N.

[cycloneye]

Tropical Storm Gilma Discussion Number 7
NWS National Hurricane Center Miami FL EP072024
800 PM PDT Mon Aug 19 2024

Gilma is looking a little more ragged on satellite imagery this
evening. Deep convection is confined to the southwest quadrant of
the circulation and the cloud top temperatures have been gradually
warming. Still, subjective Dvorak estimates from TAFB and SAB have
held steady this cycle, partially due to constraints. The initial
intensity remains at a possibly generous 50 kt.

The storm is moving westward at an estimated 9 kt. The track
reasoning has not changed. A mid-level ridge centered over the
southwestern United States is expected to turn Gilma
west-northwestward soon and steer the storm in this general
direction for the entirety of the forecast period. The forward
motion of the storm should slow in the next day or so as a
deep-layer trough off of the U.S. west coast weakens the ridge.
There is still quite a bit of spread in the model track guidance,
though the envelope has shifted southward this cycle. The official
forecast has been nudged slightly south of the previously predicted
track and remains near the various consensus aids.

The strong-to-moderate vertical wind shear is expected to abate
within a day or so according to the global models. Once this
occurs, oceanic and environmental conditions should allow for steady
strengthening, and Gilma is forecast to reach hurricane strength
late this week or early this weekend. There is a wide range in the
intensity model guidance, making this forecast somewhat uncertain.
The latest official intensity forecast is very similar to the
previous prediction and lies in the middle of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 15.2N 117.3W 50 KT 60 MPH
12H 20/1200Z 15.6N 118.7W 55 KT 65 MPH
24H 21/0000Z 16.1N 120.5W 55 KT 65 MPH
36H 21/1200Z 16.6N 122.3W 55 KT 65 MPH
48H 22/0000Z 17.1N 123.7W 60 KT 70 MPH
60H 22/1200Z 17.6N 124.9W 70 KT 80 MPH
72H 23/0000Z 18.0N 125.9W 75 KT 85 MPH
96H 24/0000Z 18.8N 128.0W 75 KT 85 MPH
120H 25/0000Z 19.6N 130.2W 60 KT 70 MPH

$$
Forecaster Bucci

[Yellow Evan]

ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Gilma Discussion Number 8
NWS National Hurricane Center Miami FL EP072024
200 AM PDT Tue Aug 20 2024

Gilma continues to struggle with moderate to strong northeasterly
vertical wind shear. The center is exposed more than 30 n mi to the
northeast of the main convective overcast area. A 20/0129 UTC SSMIS
pass and a pair of more recent ASCAT passes were helpful in placing
the center well outside of the convective area. The highest
reliable ASCAT vectors were only about 40 kt. UW-CIMSS objective
intensity estimates range from 34-42 kt. Subjective current
intensity estimates from TAFB and SAB were T-3.5/55 kt and T-3.0/45
kt from SAB. Based on the degraded structure on satellite imagery,
the ASCAT data and the objective intensity estimates from UW-CIMSS,
the initial intensity is set to 45 kt for this advisory.

The aforementioned microwave and ASCAT data indicate that the
center of the cyclone is a bit farther north than previously
estimated. It appears that Gilma has slowed down, and the motion is
estimated to be west-northwestward, or 295/7 kt. A mid-level ridge
to the north of Gilma should steer the cyclone generally
west-northwestward at a similar forward speed through the forecast
period. Although the track guidance is gradually coming into better
agreement, there is still more spread than normal among the various
track aids. The official track forecast is quite similar to the
previous NHC track prediction. The NHC forecast track is closer to
the ECMWF model than the GFS model through 72 h, and is close to an
average of those two models beyond 72 h.

Moderate to strong northeasterly vertical wind shear will continue
to affect Gilma for another 12 h or so. The SHIPS guidance indicates
that the cyclone will reach a much lower wind shear regime by 24 h.
Therefore, little change in strength is expected during the next
12-24 h, following by steady intensification. The official intensity
forecast was lowered in the short term due to the weaker initial
intensity. However, the guidance has become more aggressive after
the cyclone reaches the weaker shear, and the NHC forecast follows
suit, now showing a peak of 85 kt in 60-72 hr. The new NHC intensity
forecast is near the middle of the guidance envelope, in between the
weaker statistical guidance and the stronger regional hurricane
model dynamical guidance. SSTs along Gilma's path should decrease to
about 26C in 72 h, and remain at that value through 96 h before
dropping to below 26C. Weakening is forecast during that time
period.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0900Z 15.7N 118.3W 45 KT 50 MPH
12H 20/1800Z 16.0N 119.8W 45 KT 50 MPH
24H 21/0600Z 16.4N 121.5W 50 KT 60 MPH
36H 21/1800Z 16.8N 123.0W 60 KT 70 MPH
48H 22/0600Z 17.3N 124.2W 70 KT 80 MPH
60H 22/1800Z 17.7N 125.3W 85 KT 100 MPH
72H 23/0600Z 18.2N 126.4W 85 KT 100 MPH
96H 24/0600Z 19.0N 128.6W 75 KT 85 MPH
120H 25/0600Z 20.0N 131.2W 60 KT 70 MPH

$$
Forecaster Hagen/Pasch

[Yellow Evan]

ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Gilma Discussion Number 9
NWS National Hurricane Center Miami FL EP072024
800 AM PDT Tue Aug 20 2024

Deep convection has increased significantly over the past several
hours, but the center is located near the northeastern edge of the
thunderstorms. This asymmetric structure is due to 15-20 kt of
northeasterly vertical wind shear. The objective and subjective
Dvorak estimates range from 35 to 55 kt, and based on that data,
the initial intensity is held at 45 kt. However, this estimate
could be a little conservative based on recent satellite trends.

Gilma's motion has been somewhat erratic, but smoothing through the
wobbles yields an initial motion estimate of 285/10 kt. A high
pressure ridge situated to the north of the storm should cause that
motion to continue for another day or so. However, after that
time, a decrease in forward speed is expected as the ridge weakens
and is replaced by a broad trough. The models have trended south
this cycle, and the NHC track forecast has been nudged in that
direction.

The ongoing northeasterly vertical wind shear is expected to
decrease and become fairly low during the next few days. This more
conducive upper-level wind pattern combined with warm SSTs and high
moisture should allow Gilma to steadily strengthen through the rest
of the week. Gilma is forecast to reach hurricane strength by
Wednesday night and could reach its peak intensity a day later. By
the end of the week, the cyclone is expected to track over cooler
waters and into a more stable airmass, which should induce a
weakening trend. The NHC intensity forecast is similar to the
previous one.


FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 16.0N 119.6W 45 KT 50 MPH
12H 21/0000Z 16.2N 121.0W 50 KT 60 MPH
24H 21/1200Z 16.6N 122.6W 55 KT 65 MPH
36H 22/0000Z 17.0N 123.9W 65 KT 75 MPH
48H 22/1200Z 17.4N 125.0W 75 KT 85 MPH
60H 23/0000Z 17.8N 126.0W 85 KT 100 MPH
72H 23/1200Z 18.3N 127.3W 85 KT 100 MPH
96H 24/1200Z 19.2N 129.7W 75 KT 85 MPH
120H 25/1200Z 20.0N 132.7W 60 KT 70 MPH

$$
Forecaster Cangialosi

NNNN

[Yellow Evan]

EP, 07, 2024082018, , BEST, 0, 160N, 1202W, 55, 995, TS, 50, NEQ, 20, 30, 0, 0, 1010, 200, 30, 0, 0, E, 0, , 0, 0, GILMA, M, 0, , 0, 0, 0, 0, genesis-num, 018,

[Yellow Evan]

I think Gilma is a hurricane tbh unless you think that's rain contaminated.

[Kingarabian]

Center hasn't been exposed for most of the day. Good sign that shear is decreasing. Today's model runs have favored this getting close to Hawaii as well.

[Yellow Evan]

000
WTPZ42 KNHC 202057
TCDEP2

Tropical Storm Gilma Discussion Number 10
NWS National Hurricane Center Miami FL EP072024
200 PM PDT Tue Aug 20 2024

Gilma has become much better organized throughout the day. The
center is now embedded in the thunderstorm activity, and the
associated deep convection has been expanding and has a less sheared
appearance. The Dvorak estimates have increased and are between 45
and 55 kt at 18Z. Over the past hour or two, a pair of ASCAT passes
showed reliable winds in the 50-55 kt range. Based on the ASCAT
data and the improving satellite appearance, the initial intensity
is increased to 60 kt.

Gilma is moving westward or 280 degrees at 10 kt. A high pressure
ridge situated to the north of the storm should cause it to continue
westward to west-northwestward at about the same speed for another
day or so. However, after that time, a decrease in forward speed
and a slight turn to the right are expected as the ridge weakens and
is replaced by a broad trough. The NHC track forecast has again
been nudged to the south, toward the latest consensus aids.

The improving cloud pattern suggests that the vertical wind shear
around Gilma is lessening. In addition, the storm is forecast to
remain over warm waters and in a relatively moist airmass for a few
days. Therefore, continued steady strengthening is predicted, and
Gilma is expected to become a hurricane tonight or early Wednesday
with additional strengthening anticipated through Thursday. By the
end of the week, however, the cyclone is expected to track over
cooler waters and into a more stable airmass, which should induce a
weakening trend. The NHC intensity forecast is nudged upward from
the previous one and near the high end of the model guidance.

The initial 34- and 50-kt wind radii have been updated using the
aforementioned ASCAT data.


FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 16.1N 120.6W 60 KT 70 MPH
12H 21/0600Z 16.3N 121.9W 65 KT 75 MPH
24H 21/1800Z 16.6N 123.2W 70 KT 80 MPH
36H 22/0600Z 17.0N 124.4W 75 KT 85 MPH
48H 22/1800Z 17.5N 125.5W 85 KT 100 MPH
60H 23/0600Z 17.9N 126.6W 90 KT 105 MPH
72H 23/1800Z 18.4N 128.0W 85 KT 100 MPH
96H 24/1800Z 19.0N 130.6W 75 KT 85 MPH
120H 25/1800Z 19.8N 134.1W 60 KT 70 MPH

$$
Forecaster Cangialosi

[xtyphooncyclonex]

GFS turns this into a whole typhoon/hurricane around the IDL. Shows Gilma lingering for days and days

[Hurricane2022]

Looks much better now, but she still has some good work to do, MW says.


Gilma is likely on the way to become a bonafide and classic OTS EPAC major hurricane, unless this (also) directly affects Hawaii.

[Kingarabian]

GFS turns this into a whole typhoon/hurricane around the IDL. Shows Gilma lingering for days and days

Models show a window for better UL conditions in the CPAC compared to 90E/91E. Possibility if this can get going and become a major hurricane that it could get some serious ACE if it pumps the ridge and goes south of the islands.

[lilbump3000]

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

[Yellow Evan]

000
WTPZ42 KNHC 210234
TCDEP2

Tropical Storm Gilma Discussion Number 11
NWS National Hurricane Center Miami FL EP072024
800 PM PDT Tue Aug 20 2024

Gilma is holding steady this evening. The low-level circulation is
still hidden beneath a modest Central Dense Overcast (CDO). Recent
satellite microwave imagery showed the deep convection is limited to
the southern half of the storm, with a band extending to the
southwest of the center. The initial intensity is held at 60 kt in
deference to the earlier ASCAT data, slightly above the subjective
Dvorak estimates of 55 kt from TAFB and SAB.

A ridge centered over the southwestern U.S. is steering the storm at
an estimated 275/9 kt. A westward to west-northwestward motion
should continue for the next day or so. By Thursday, a slight turn
poleward and decrease of forward speed is expected as a deep-layer
trough moving in from the west erodes the ridge. Once again, the
track model guidance has shifted southward this cycle. The latest
NHC track forecast has been nudged to the south and lies between the
previous track forecast and the simple consensus aid TVCE.

Gilma seems to be holding its own against the moderate northeasterly
wind shear. Global models suggest the upper-level winds should
gradually become more favorable over the next day or so, allowing
Gilma to reach hurricane status overnight or Wednesday morning. The
storm should have the necessary ingredients to steadily strengthen
through Thursday, and the forecast peak remains at 90 kt. By the end
of the week and into the weekend, Gilma should encounter cooling sea
surface temperatures, increasing shear, and dry mid-level humidities
causing it to gradually weaken. The latest official forecast is
largely an update of the previous prediction.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0300Z 16.1N 121.5W 60 KT 70 MPH
12H 21/1200Z 16.2N 122.6W 65 KT 75 MPH
24H 22/0000Z 16.6N 123.9W 70 KT 80 MPH
36H 22/1200Z 17.0N 125.0W 80 KT 90 MPH
48H 23/0000Z 17.4N 126.1W 85 KT 100 MPH
60H 23/1200Z 17.8N 127.3W 90 KT 105 MPH
72H 24/0000Z 18.2N 128.6W 85 KT 100 MPH
96H 25/0000Z 18.8N 131.6W 70 KT 80 MPH
120H 26/0000Z 19.6N 135.4W 55 KT 65 MPH

$$
Forecaster Bucci