EPAC: COSME - Remnant - Discussion

[Yellow Evan]

Nice curved band feature forming. This too might be classifiable.

[cycloneye]

5 AM PDT:

Offshore of Southwestern Mexico (EP91):
Showers and thunderstorms associated with an area of low pressure
located about 600 miles southwest of the southwestern coast of
Mexico have become better organized overnight. Further development
of this system is expected, and a tropical depression or tropical
storm is likely to form later today or tonight as it moves
northwestward at 5 to 10 mph. For more information on this system,
including gale warnings, see High Seas Forecasts issued by the
National Weather Service.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 7 days...high...90 percent.

[cycloneye]

Up to 2.0.

A. TROPICAL DISTURBANCE (91E)

B. 08/1130Z

C. 12.5N

D. 110.4W

E. THREE/GOES-W

F. T2.0/2.0

G. IR/EIR/VIS

H. REMARKS...3.5/10 BANDING RESULTS IN A DT OF 2.0. THE MET IS 1.5. THE
PT IS 2.0. THE FT IS BASED ON THE DT.

I. ADDL POSITIONS

NIL


...BERTALAN

Not a TD?

EP, 91, 2025060812, , BEST, 0, 123N, 1104W, 30, 1001, LO

[Kingarabian]

Shear has shifted to easterly but its moving NW vs WNW. The track and interaction with Barbara could limit this. Has been a TD for the past 6 hours at least though.

[Subtrop]

Tropical Depression Three-E Discussion Number 1
NWS National Hurricane Center Miami FL EP032025
800 AM MST Sun Jun 08 2025

Showers and thunderstorms associated with the area of low pressure
well southwest of the coast of southwestern Mexico have shown
considerable improvement this morning. Well-organized curved bands
have been present during the last 6-12 hours with deep convection
building near the low-level center. The latest subjective Dvorak
intensity estimates from TAFB and SAB came in at 1.5/25 kt and
2.0/30 kt, respectively. Additionally, overnight satellite-derived
wind data showed 30 kt winds in the northwest quadrant of the low
pressure area. Given the improved convective organization and data
suggesting maximum sustained winds of 30 kt, Tropical Depression
Three-E has now formed with the initial intensity set at 30 kt.

The initial motion of Tropical Depression Three-E is set at 310/07
kt. This general motion is expected to continue today and tonight,
followed by a much more uncertain motion Monday through mid-week due
to the expected interaction with Tropical Storm Barbara. This
interaction will likely result in a decrease in forward speed and a
more northward to northeastward motion on Monday, followed by an
increase in forward speed and a shift back to the northwest by
Tuesday. The track forecast generally follows the consensus
guidance, which is in between the two extremes of the GFS and ECMWF
models.

Tropical Depression Three-E is forecast to remain in a low to
moderate vertical wind shear environment with warm sea surface
temperatures of 27 to 28C and abundant deep layer moisture during
the next couple days. This should allow for steady strengthening,
and the system will likely become a tropical storm later today. By
Monday night, the tropical cyclone will begin to move over much
cooler water below 26C, and this in combination with the interaction
with Barbara should result in rather rapid weakening, with the
system becoming a post-tropical remnant low by Thursday morning. The
intensity forecast is roughly a split of the statistical and
dynamical consensus guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 08/1500Z 12.6N 110.6W 30 KT 35 MPH
12H 09/0000Z 13.3N 111.6W 40 KT 45 MPH
24H 09/1200Z 14.2N 112.7W 50 KT 60 MPH
36H 10/0000Z 14.7N 113.9W 60 KT 70 MPH
48H 10/1200Z 15.2N 114.0W 60 KT 70 MPH
60H 11/0000Z 15.7N 113.9W 50 KT 60 MPH
72H 11/1200Z 16.9N 113.2W 30 KT 35 MPH
96H 12/1200Z 18.3N 114.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 13/1200Z...DISSIPATED

$$
Forecaster Jelsema/Cangialosi

[Sciencerocks]

[cycloneye]

Hello Cosme.

EP, 03, 2025060818, , BEST, 0, 130N, 1107W, 40, 999, TS, 34, NEQ, 40, 30, 0, 40, 1009, 200, 40, 0, 0, E, 0, , 0, 0, COSME, M

https://ftp.nhc.noaa.gov/atcf/btk/bep032025.dat

[Yellow Evan]

A bit stronger than that per recent ASCAT.

[Kingarabian]

CDO covering the LLC. Still on the leading edge though which will limit its intensity.

[cycloneye]

Tropical Storm Cosme Discussion Number 2
NWS National Hurricane Center Miami FL EP032025
200 PM MST Sun Jun 08 2025

Deep convection has been increasing near the center and in curved
bands on the western side of the circulation during the past
several hours. An ASCAT-C pass from a few hours ago showed peak
winds in the 35-40 kt range, and based on that data, the depression
has been upgraded to Tropical Storm Cosme with the initial
intensity set at 40 kt.

Cosme will likely continue to strengthen for the next day or two as
it remains in an environment of low to moderate wind shear, abundant
moisture, and over warm SSTs. The NHC intensity forecast shows a
peak of 60 kt at 24 and 36 hours, and it wouldn't be surprising if
Cosme becomes a hurricane during that time frame. By mid-week,
however, the storm is expected to move over progressively cooler
waters and into a drier airmass, which should cause the system to
begin weakening. Cosme is now forecast to become a remnant low in 3
days and dissipate in 4 days.

The storm is moving northwestward at 7 kt, and that general motion
is expected to continue during the next couple of days. After that
time, the interaction with Barbara will likely result in an initial
slow down and then turn to the northeast. There is a fair amount of
spread in the guidance due to the complexity of this interaction.
The NHC track forecast has been adjusted a little to the right of
the previous one to account for the initial motion/position and to
be in better agreement with the latest consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 08/2100Z 13.3N 111.0W 40 KT 45 MPH
12H 09/0600Z 14.0N 111.9W 50 KT 60 MPH
24H 09/1800Z 14.7N 113.1W 60 KT 70 MPH
36H 10/0600Z 15.1N 113.7W 60 KT 70 MPH
48H 10/1800Z 15.5N 113.7W 55 KT 65 MPH
60H 11/0600Z 16.4N 113.0W 45 KT 50 MPH
72H 11/1800Z 17.5N 112.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 12/1800Z...DISSIPATED

$$
Forecaster Cangialosi

[Sciencerocks]

[Kingarabian]

This might have a better chance at attaining hurricane status vs Barbara. Mid shear becomes favorable in 6 or so hours.

[cycloneye]

Remains at 40kt.

EP, 03, 2025060900, , BEST, 0, 135N, 1115W, 40, 999, TS

https://ftp.nhc.noaa.gov/atcf/btk/bep032025.dat

[Sciencerocks]

[cycloneye]

Tropical Storm Cosme Discussion Number 3
NWS National Hurricane Center Miami FL EP032025
800 PM MST Sun Jun 08 2025

Cosme is gradually improving in organization with deep convection
pulsing, albeit with the center on the northern edge of the
convection. A recent microwave pass did show a prominent curved
band especially in the southern semicircle of the storm. The
initial wind speed will stay at 40 kt for this advisory, between
the lower subjective Dvorak estimates and higher objective values.

Conditions look conducive for strengthening for about the next 24
hours while Cosme moves within a fairly low shear and warm SST
environment. Thereafter, some increase in easterly shear is
possible, and the storm should move over a tight SST gradient into a
drier airmass. Cosme is forecast to respond to these conditions by
weakening quickly by midweek. The only change to the previous
forecast is a small reduction in the intensity forecast at 60 and 72
h, consistent with the latest model consensus. It would not be
surprising to see Cosme become a remnant low faster than shown
below.

The storm continues moving northwestward at 8 kt, and a
west-northwest to northwest motion is anticipated during the next
day or so. After that time, Tropical Storm Barbara causes a
mid-level ridge to erode, and Cosme should respond by taking a
sharp turn to the northeast around Barbara. Model guidance has
shifted notably to the left this evening, suggesting a
little more separation of the tropical cyclones before they
interact. While the new forecast is adjusted to the west, this is
not a particularly confident longer-range forecast due to
the complexity of the interaction.

FORECAST POSITIONS AND MAX WINDS

INIT 09/0300Z 13.7N 111.9W 40 KT 45 MPH
12H 09/1200Z 14.4N 112.9W 50 KT 60 MPH
24H 10/0000Z 14.9N 114.1W 60 KT 70 MPH
36H 10/1200Z 15.3N 114.2W 60 KT 70 MPH
48H 11/0000Z 15.8N 113.8W 55 KT 65 MPH
60H 11/1200Z 16.9N 113.0W 40 KT 45 MPH
72H 12/0000Z 18.5N 113.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 13/0000Z...DISSIPATED

$$
Forecaster Blake

Tropical Storm Cosme Discussion Number 4
NWS National Hurricane Center Miami FL EP032025
200 AM MST Mon Jun 09 2025

The satellite presentation of Cosme has continued to gradually
improve since the previous advisory, with sustained deep convection
holding over the low-level center. A timely 09/0524Z ASCAT pass
helped with the initial intensity and 34 kt wind radii estimates,
with several wind barbs showing 40 to 45 knot winds. The latest
subjective Dvorak intensity estimates from TAFB and SAB were T3.0/45
knots and T2.5/35 knots respectively. Meanwhile, the objective
Dvorak satellite estimates range from 40 to 50 knots. The initial
intensity has been adjusted up to 45 knots with this advisory
package, in line with the most recent ASCAT pass.

Cosme is moving toward west-northwest at 8 kt. This general motion
is expected to continue during the next 24 hours to the south of a
mid-level ridge, with a gradual slowing in forward speed. Tonight
and Tuesday Barbara is forecast to erode the mid-level ridge to the
north of Cosme, resulting in a further slowing in motion and a shift
to the north. An increase in forward speed and a motion to the
north-northeast is expected Tuesday night, with Cosme forecast to
become a post-tropical remnant low on Wednesday. The latest track
forecast is very close to that of the previous advisory and is
generally a blend of the consensus guidance.

Environmental conditions continue to look conducive for
strengthening of Cosme during the next 24 hours or so. Vertical wind
shear will lighten up some while the system passes over 27/28C water
with abundant deep layer moisture. The intensity forecast is similar
to the previous advisory, bringing Cosme close to hurricane strength
late today or tonight. Beyond 24 hours, vertical wind shear is
forecast to increase and mid-level moisture is forecast to decrease,
which should lead to a gradual weakening of Cosme. A more rapid
weakening is then expected by Wednesday as the system moves over
much cooler water, with Cosme expected to dissipate by 96 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 09/0900Z 14.2N 112.8W 45 KT 50 MPH
12H 09/1800Z 14.6N 113.5W 55 KT 65 MPH
24H 10/0600Z 15.0N 114.2W 60 KT 70 MPH
36H 10/1800Z 15.4N 114.2W 55 KT 65 MPH
48H 11/0600Z 16.5N 113.4W 45 KT 50 MPH
60H 11/1800Z 17.9N 113.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 12/0600Z 19.0N 113.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 13/0600Z...DISSIPATED

$$
Forecaster Jelsema/Hagen

[Yellow Evan]

In theory the environment is favorable for another 36 hours but I still think Barbara could cause some unexpected shear.

[Sciencerocks]

[Yellow Evan]

000
WTPZ43 KNHC 092031
TCDEP3

Tropical Storm Cosme Discussion Number 6
NWS National Hurricane Center Miami FL EP032025
200 PM MST Mon Jun 09 2025

Cosme continues to intensify and is nearing hurricane strength.
Visible satellite images show that the convective bands have
consolidated near the center, and there is some evidence of a
partial inner core. A blend of the latest objective and subjective
satellite intensity estimates support increasing the initial
intensity to 60 kt. A partial ASCAT pass indicates that the
wind field of Cosme is quite compact, and the initial wind radii
have been updated based on that data.

Some additional strengthening is possible in the short term, and
Cosme could become a hurricane tonight while it remains in
generally conducive environmental conditions. However, the
combination of decreasing SSTs and intrusions of dry/stable air
should end the strengthening trend by early Tuesday and then cause a
quick weakening. Simulated satellite images from the GFS and ECMWF
models show deep convection vanishing by Wednesday, and based on
that guidance, the transition to a remnant low has been moved up to
48 hours. Dissipation is likely to occur in 3 to 4 days.

The storm is moving northwestward at 8 kt, and this general motion
should continue through tonight. After that time, a turn to the
north or north-northeast is expected as Cosme moves toward a
weakness left behind by Hurricane Barbara to its northeast. The
NHC track forecast is in fair agreement with the consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 15.0N 113.9W 60 KT 70 MPH
12H 10/0600Z 15.3N 114.5W 65 KT 75 MPH
24H 10/1800Z 15.8N 114.5W 60 KT 70 MPH
36H 11/0600Z 16.6N 113.8W 50 KT 60 MPH
48H 11/1800Z 17.8N 113.2W 35 KT 40 MPH...POST-TROPICAL
60H 12/0600Z 19.2N 113.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 12/1800Z 20.1N 113.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 13/1800Z...DISSIPATED

$$
Forecaster Cangialosi

[Sciencerocks]

[cycloneye]

Shy of cane at 00z.

EP, 03, 2025061000, , BEST, 0, 150N, 1141W, 60, 992, TS