EPAC: GILMA - Post-Tropical - Discussion

[Subtrop]

EP, 99, 2024081612, , BEST, 0, 120N, 1027W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1010, 150, 100, 0, 0, E, 0, , 0, 0, INVEST, S, 0, , 0, 0, 0, 0, genesis-num, 018,

https://ftp.nhc.noaa.gov/atcf/btk/bep992024.dat

[Kingarabian]

For the eastern North Pacific...east of 140 degrees west longitude:

1. Well Offshore of Southwestern Mexico (EP99):
A broad area of low pressure located several hundred miles off the
southwestern coast of Mexico is producing a large area of
disorganized showers and thunderstorms to the west of its center.
Upper-level winds are forecast to become more conducive for gradual
development of this system over the weekend, and a tropical
depression is likely to form early next week while it moves
west-northwestward at about 10 mph across the central portion of the
East Pacific basin.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 7 days...high...80 percent

[Yellow Evan]

Environment appears good if this can avoid interaction with disturbance to its west but at a certain point it’s going to drift north into low SSTs.

[lilbump3000]

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

[ElectricStorm]

Last couple GFS runs are back to showing this becoming a strong hurricane. Since this one shouldn't affect any land, it would be nice if we can finally get something stronger than a Cat 1 in the EPAC

[cycloneye]

Well Offshore of Southwestern Mexico (EP99):
A broad area of low pressure located several hundred miles off the
southwestern coast of Mexico continues to produce a distinct area of
showers and thunderstorms that are showing signs of organization.
Upper-level winds are forecast to be generally conducive for
additional development of this system through the weekend, and a
tropical depression is likely to form in the next couple of days
while it moves west-northwestward at about 10 to 15 mph across the
central portion of the eastern Pacific.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 7 days...high...90 percent.

[Yellow Evan]

Well Offshore of Southwestern Mexico (EP99):
An area of low pressure located several hundred miles off the
southwestern coast of Mexico is producing showers and thunderstorms
that continue to show signs of organization. Recently-received
microwave satellite imagery also suggests the system is developing a
well-defined center, and if these trends continue, a tropical
depression is likely to form as soon as later today. The system is
forecast to move west-northwestward at about 10 to 15 mph across the
central portion of the eastern Pacific during the next several
days.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 7 days...high...90 percent.

[Yellow Evan]

TXPZ28 KNES 181228
TCSENP

A. TROPICAL DISTURBANCE (99E)

B. 18/1200Z

C. 14.5N

D. 110.7W

E. FIVE/GOES-W

F. T1.5/1.5

G. IR/EIR/SWIR

H. REMARKS...AN LLCC WITH CIRCULARLY DEFINED CLOUD LINES LOCATED NEAR
THE LARGE COLD OVERCAST YIELDS A DT OF 2.0. THE MET IS 1.5 BASED ON A
SLOW DEVELOPMENT 24 HOUR TREND. THE PT AGREES. THE FT IS BASED ON THE
MET DUE TO THE FLUCTUATING CONVECTION.

I. ADDL POSITIONS

NIL


...BROWN

[Yellow Evan]

[Subtrop]

EP, 07, 2024081812, , BEST, 0, 145N, 1102W, 30, 1007, LO, 34, NEQ, 0, 0, 0, 0, 1009, 120, 70, 0, 0, E, 0, , 0, 0, SEVEN-E, S, 0, , 0, 0, 0, 0, genesis-num, 018, TRANSITIONED, epA92024 to ep072024,

https://www.ssd.noaa.gov/PS/TROP/DATA/A ... 072024.dat

[DorkyMcDorkface]

HWRF is the strongest of the hurricane models, making it a borderline donut.

[lilbump3000]

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

[Kingarabian]

HWRF is the strongest of the hurricane models, making it a borderline donut.
https://i.ibb.co/5k0Y4rb/hwrf-sat-IR-99-E-22.png

Depends on the heading. If it can maintain a WNW that structure makes a lot of sense.

[Kingarabian]

https://i.imgur.com/hTLFT0r.gif

Don't have any expectations but this has the look of a classic EPAC forming.

[Kingarabian]

Looks like we have Gilma.

[cycloneye]

Tropical Storm Gilma Discussion Number 2
NWS National Hurricane Center Miami FL EP072024
200 PM MST Sun Aug 18 2024

Despite continued moderate easterly vertical wind shear, deep
convection has been expanding and has now built over the center of
the system. Accordingly, the Dvorak estimates have nudged upward
and are now between 30 and 35 kt. Based on those classifications
and the improving convective pattern, the initial intensity is
increased to 35 kt, making the system Tropical Storm Gilma.

Moderate easterly vertical wind shear of about 20 kt is expected to
continue during the next day or so, which should limit the amount of
strengthening in the short term. The shear is expected to lessen
some after that, and the somewhat more favorable upper-level wind
environment combined with warm waters and a relatively moist
atmosphere should allow for gradual strengthening throughout much of
the week. The NHC intensity forecast is higher than the previous
one and roughly between the HCCA and IVCN guidance.

Gilma is moving west-northwestward, or 285 degrees, at 12 kt. A
high pressure ridge situated to the system’s north should cause the
storm to move westward to west-northwestward at about the same speed
during the next couple of days. Later in the week, the models show
the ridge weakening as a trough amplifies off the west coast of the
U.S., which should cause the system to slow down and turn a bit to
the right. There is quite a bit of along-track spread in the
models, with the GFS being the slowest model and HWRF/HAFS the
fastest. The NHC track forecast is similar to the previous one
through 60 h and then is a little to the north of the prior track
after that. This forecast is close to the various consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 18/2100Z 14.7N 112.3W 35 KT 40 MPH
12H 19/0600Z 15.1N 114.0W 40 KT 45 MPH
24H 19/1800Z 15.6N 116.1W 40 KT 45 MPH
36H 20/0600Z 15.9N 118.1W 45 KT 50 MPH
48H 20/1800Z 16.2N 119.9W 50 KT 60 MPH
60H 21/0600Z 16.6N 121.3W 55 KT 65 MPH
72H 21/1800Z 16.9N 122.5W 60 KT 70 MPH
96H 22/1800Z 17.7N 125.0W 70 KT 80 MPH
120H 23/1800Z 18.6N 127.1W 70 KT 80 MPH

$$
Forecaster Cangialosi

[lilbump3000]

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

[Yellow Evan]

I’m a bit more worried about this struggling due to shear than the NHC thinks but global models are not handling this well at all and are still playing catch up.

18z GFS for example has vorticity to its west being dominant after it randomly amplifies tomorrow.

[cycloneye]

Tropical Storm Gilma Discussion Number 3
NWS National Hurricane Center Miami FL EP072024
800 PM MST Sun Aug 18 2024

Gilma continues to battle easterly shear this evening.
Deep convection has been regularly pulsing near the center and
then pulled off toward the western side of the circulation.
Subjective Dvorak estimates from TAFB and SAB were T3.0/45 kt and
T2.0/30 kt, respectively. Objective intensity estimates range from
30 to 38 kt. The initial intensity is held at 35 kt, representing a
blend of the various estimates.

Strong-to-moderate deep vertical wind shear is forecast to persist
for the next day or two. Global models vary when the shear will
relax, but sometime on Tuesday or Wednesday Gilma should be in a
more conducive environment and gradually strengthen. By the end of
the forecast period, the storm is expected to move into a drier
airmass with increasing upper-level winds, which should induce
gradual weakening. The latest intensity forecast is very similar to
the previous prediction, slightly higher than the various consensus
aids.

Gilma is moving westward along the south side of a mid-level ridge
at 280/11 kt. A westward to west-northwestward motion should
continue for the next couple of days. By Wednesday, Gilma is
expected to slow down and turn more northwestward when a trough
off of the west coast of the United States erodes the ridge. There
is quite a bit of model spread during this period, with the GFS
showing a slower forward speed and a more poleward turn compared to
some of the regional models which stay farther to the south and
move faster. The official track forecast lies near the simple
consensus aids and is slightly south of the previous track through
60 h and a little to the north afterwards.


FORECAST POSITIONS AND MAX WINDS

INIT 19/0300Z 14.8N 113.5W 35 KT 40 MPH
12H 19/1200Z 15.2N 115.2W 40 KT 45 MPH
24H 20/0000Z 15.5N 117.3W 40 KT 45 MPH
36H 20/1200Z 15.8N 119.2W 45 KT 50 MPH
48H 21/0000Z 16.3N 120.7W 50 KT 60 MPH
60H 21/1200Z 17.1N 122.5W 55 KT 65 MPH
72H 22/0000Z 17.5N 123.5W 60 KT 70 MPH
96H 23/0000Z 18.3N 125.5W 70 KT 80 MPH
120H 24/0000Z 19.1N 127.8W 65 KT 75 MPH

$$
Forecaster Bucci

[cycloneye]

Tropical Storm Gilma Discussion Number 4
NWS National Hurricane Center Miami FL EP072024
200 AM MST Mon Aug 19 2024

A large convective burst formed during the evening and overnight
hours with cloud tops as cold as -80C, and the center of Gilma
seems to be underneath the eastern edge of the deep convection.
This represents a change from 6 h ago, when the center had been a
bit more exposed near the eastern edge of a weaker area of central
convection. The convective burst has weakened a bit during the last
hour or so, and moderate northeasterly shear still appears to be
affecting Gilma. A 19/0412 UTC ASCAT-B pass missed the center of
the cyclone, but it did measure winds up to 40 kt to the east of
the center. It is uncertain whether these vectors are located near
or outside of Gilma's radius of maximum winds. Subjective
intensity estimates are T-3.0/45 kt from TAFB and T-2.0/30 kt from
SAB. The objective intensity estimates from CIMSS range from 35 to
43 kt, about a 5 kt increase from 6 h ago. Based on the ASCAT data
and latest satellite intensity estimates, the initial intensity is
raised to 45 kt for this advisory.

Moderate-to-strong northeasterly vertical wind shear is expected to
persist for at least another 36 h, and only slow intensification is
forecast in the short term. After that time, the shear is forecast
to relax some, and Gilma should be in a more conducive environment
for strengthening by Tuesday night or Wednesday. By the end of the
forecast period, Gilma is expected to move into a drier and more
stable environment, which should begin to induce weakening. The
latest intensity forecast is slightly higher than the previous
official forecast in the short term due to the higher initial
intensity, but after that is similar to the previous forecast. The
intensity forecast is slightly lower than the model consensus during
the first 48 h and is near the consensus thereafter.

Gilma is still moving westward along the south side of a mid-level
ridge at about 280/11 kt. A similar motion should continue for the
next 24 h followed by a gradual turn to the west-northwest. By
Wednesday, Gilma should slow down a bit and turn more northwestward
when a trough off the west coast of the United States erodes the
ridge. The model spread is quite large through the forecast period,
with the GFS being the largest outlier, showing a track well to the
north-northeast of the rest of the guidance. Part of the reason for
this is how the GFS model handles the interaction with the
aforementioned trough, but part of the reason may also be because
the GFS model shows a different interaction with a tropical
disturbance currently located several hundred miles to the west of
Gilma, mentioned in the latest Tropical Weather Outlook. The
official track is quite similar to the previous one and lies just a
touch south of the consensus aids beyond 48 h.


FORECAST POSITIONS AND MAX WINDS

INIT 19/0900Z 15.0N 114.6W 45 KT 50 MPH
12H 19/1800Z 15.2N 116.3W 45 KT 50 MPH
24H 20/0600Z 15.5N 118.2W 50 KT 60 MPH
36H 20/1800Z 16.0N 119.8W 50 KT 60 MPH
48H 21/0600Z 16.7N 121.5W 55 KT 65 MPH
60H 21/1800Z 17.3N 122.7W 65 KT 75 MPH
72H 22/0600Z 17.8N 123.9W 70 KT 80 MPH
96H 23/0600Z 18.6N 125.9W 70 KT 80 MPH
120H 24/0600Z 19.5N 128.3W 60 KT 70 MPH

$$
Forecaster Hagen/Pasch