EPAC: COSME - Remnant - Discussion

[cycloneye]

Here are for the record the last 4 advisories.

https://www.nhc.noaa.gov/archive/2025/COSME.shtml?

[cycloneye]

Tropical Storm Cosme Discussion Number 7
NWS National Hurricane Center Miami FL EP032025
800 PM MST Mon Jun 09 2025

Cosme remains at the threshold of hurricane strength. Convection
continues to be potent south and east of the center, though it is
weak on the northwestern side. Unfortunately there haven't been any
recent microwave passes to assess the inner-core structure. Since
the latest blend of objective and subjective satellite intensity
estimates remains near 60 kt, that value will be kept as the
initial wind speed.

Cosme is moving along a thermal ridge in the SSTs, and it still
could become a hurricane overnight before reaching less favorable
conditions tomorrow morning. Steady or rapid weakening is probable
by late Tuesday due to a combination of decreasing SSTs and
intrusions of dry/stable air. The tropical cyclone should lose all
convection early on Wednesday and become a remnant low between 36
and 48 h. No significant changes were made on this advisory to the
intensity forecast.

The storm has slowed down, only moving northwestward at 3 kt, and
this general motion should continue through tonight. After that
time, a turn to the north-northeast is expected as Cosme moves
toward a weakness left behind by Hurricane Barbara to its northeast.
The NHC track forecast is basically an update of the previous one,
near or a smidge left of the consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 15.2N 114.2W 60 KT 70 MPH
12H 10/1200Z 15.5N 114.5W 60 KT 70 MPH
24H 11/0000Z 15.9N 114.3W 50 KT 60 MPH
36H 11/1200Z 16.9N 113.5W 40 KT 45 MPH
48H 12/0000Z 18.2N 113.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 12/1200Z 19.3N 113.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 13/0000Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Tropical Storm Cosme Discussion Number 8
NWS National Hurricane Center Miami FL EP032025
200 AM MST Tue Jun 10 2025

The convective appearance of Cosme has changed little since the
previous advisory. The latest subjective Dvorak estimates from
TAFB and SAB range from 55-65 kt, and the latest objective
intensity estimates from UW-CIMSS range from 54-59 kt. The initial
intensity is held at 60 kt for this advisory, based on a blend of
the intensity estimates.

Cosme continues to move very slowly toward the northwest, with
motion estimated at 300/4 kt. A slow motion, perhaps more toward
the north, should continue for at least the next 12 h since the
overall steering currents are weak, due to Barbara's current
position in relation to Cosme. However, as Barbara weakens, Cosme
will accelerate north-northeastward in response to ridging located
to the northwest of the cyclone. Very little change has been made
to the NHC track forecast, and the latest forecast is near the
various consensus models.

Cosme is forecast to remain in favorable enough conditions for the
next 24 h such that the cyclone might be able to maintain its
intensity or only weaken very slowly. However, after that time, as
Cosme gains latitude, it will encounter cooler water and drier air.
Cosme is forecast to lose its convection and become post-tropical on
Wednesday, in agreement with the GFS and ECMWF simulated satellite
imagery products. The post-tropical low is then forecast to
gradually weaken and dissipate by 72 h. The NHC intensity forecast
is similar to the previous one, and is near the middle of the
guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 15.3N 114.5W 60 KT 70 MPH
12H 10/1800Z 15.5N 114.6W 55 KT 65 MPH
24H 11/0600Z 16.2N 114.1W 50 KT 60 MPH
36H 11/1800Z 17.4N 113.4W 35 KT 40 MPH...POST-TROPICAL
48H 12/0600Z 18.7N 113.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 12/1800Z 19.8N 113.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 13/0600Z...DISSIPATED

$$
Forecaster Hagen/Gibbs

Tropical Storm Cosme Discussion Number 9
NWS National Hurricane Center Miami FL EP032025
800 AM MST Tue Jun 10 2025

Moderate northeasterly shear appears to be displacing Cosme's deep
convection to the southwestern quadrant of the circulation.
Subjective and objective satellite intensity estimates have begun
to decrease, and a blend of these data support an initial intensity
of 55 kt. The shear affecting the cyclone is not expected to abate
during the next 24 hours, and with Cosme already seeming to be
ingesting more stable air, continued weakening is likely over the
next day or two. In fact, simulated satellite imagery from the
GFS, ECMWF, and high-resolution hurricane models all suggest that
Cosme's deep convection could dissipate by tonight, and the NHC
forecast therefore shows the cyclone becoming post-tropical in 24
hours. After that time, continued weakening is forecast while the
remnant low moves over colder waters, and dissipation is expected
by Friday.

Due to its position to the southwest of Barbara, Cosme's motion has
slowed down considerably, and it is estimated to be moving toward
the northwest (325 deg) at about 3 kt. While the interaction with
Barbara continues, Cosme is expected to turn toward the north and
north-northeast and accelerate a bit over the next day or two. The
new NHC forecast is not too different from the previous prediction,
and perhaps shows more of a bend back to the northwest around 60
hours, following the latest consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 15.5N 114.6W 55 KT 65 MPH
12H 11/0000Z 15.8N 114.5W 45 KT 50 MPH
24H 11/1200Z 16.6N 113.9W 40 KT 45 MPH...POST-TROPICAL
36H 12/0000Z 17.8N 113.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 12/1200Z 18.8N 113.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 13/0000Z 19.6N 114.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 13/1200Z...DISSIPATED

$$
Forecaster Berg/Gibbs

[Sciencerocks]

[cycloneye]

Tropical Storm Cosme Discussion Number 10
NWS National Hurricane Center Miami FL EP032025
200 PM PDT Tue Jun 10 2025

Although Cosme's low-level center is obscured by high-level cirrus,
it does appear to be displaced a bit to the northeast of the
remaining deep convection. Satellite intensity estimates have
continued to decrease, with objective numbers ranging between 35-45
kt, and subjective Dvorak CI numbers between 45-55 kt. The advisory
intensity is set at 45 kt based on a blend of these numbers. An
earlier ASCAT pass showed winds just over 40 kt in the southwestern
quadrant, but the southeastern quadrant, where there could be
stronger winds, was not sampled.

ASCAT and recent visible imagery suggest Cosme's center is a little
west of where it was placed this morning. Still, the storm has
turned north-northwestward with an initial motion of 330/3 kt.
Cosme is expected to turn northward and then northeastward and
speed up a bit through Wednesday, before turning back to the
north-northwest on Thursday. This track will take Cosme over
progressively cooler waters and into a drier, more stable
environment. Combined with moderate-to-strong northeasterly shear,
these conditions should cause quick weakening, and GFS- and
ECWMF-based simulated satellite images suggest that Cosme will lose
its deep convection overnight. As a result, the NHC official
forecast shows Cosme becoming a remnant low within 24 hours, with
dissipation now expected by 60 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 10/2100Z 15.8N 115.1W 45 KT 50 MPH
12H 11/0600Z 16.2N 114.8W 35 KT 40 MPH
24H 11/1800Z 17.1N 114.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 12/0600Z 18.2N 113.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 12/1800Z 19.1N 114.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 13/0600Z...DISSIPATED

$$
Forecaster Berg

[cycloneye]

Still a TS but fading fast.

EP, 03, 2025061100, , BEST, 0, 158N, 1150W, 40, 1005, TS

[cycloneye]

Tropical Storm Cosme Discussion Number 11
NWS National Hurricane Center Miami FL EP032025
800 PM MST Tue Jun 10 2025

Cosme is quickly on the path to becoming a remnant low. Satellite
images show that the low- and mid-level centers have separated,
with the low-level circulation well northeast of the mid-level one
now. Dvorak intensity estimates continue to fall, and the initial
intensity is set to 40 kt. Further weakening is anticipated due to
persistent shear, cool waters and dry air entrainment. Cosme
should transition into a remnant low on Wednesday morning and
totally dissipate in a couple of days.

The storm has taken its long-awaited turn, now moving slowly to the
north-northeast. Cosme, or what's left of it, should move a
little faster to the north late Wednesday and then dissipate into a
trough of low pressure due to unfavorable environmental conditions.
No significant changes were made to the track or intensity
forecasts.


FORECAST POSITIONS AND MAX WINDS

INIT 11/0300Z 15.9N 114.9W 40 KT 45 MPH
12H 11/1200Z 16.4N 114.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 12/0000Z 17.3N 114.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 12/1200Z 18.4N 114.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 13/0000Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Tropical Storm Cosme Discussion Number 12
NWS National Hurricane Center Miami FL EP032025
200 AM MST Wed Jun 11 2025

Drier mid-level air and stable atmospheric conditions have taken
their toll on Cosme. The system has been devoid of deep convection
for several hours and is expected to become a remnant low later this
morning. Dvorak intensity estimates continue to decrease
accordingly. A 11/0442 UTC ASCAT pass showed winds in the 35-40 kt
range in the southern semicircle. Assuming additional weakening
after that time, the initial intensity is set at 35 kt. After
transitioning to a remnant low later this morning, Cosme is expected
to dissipate by late Thursday or Friday.

The storm is now moving slowly toward the northeast. A gradual turn
to the north-northeast with some acceleration is expected later
today, followed by a turn to the north on Thursday. Only a slight
eastward adjustment was made to the previous NHC track forecast,
with no significant changes to the intensity forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 11/0900Z 16.2N 114.5W 35 KT 40 MPH
12H 11/1800Z 16.7N 114.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 12/0600Z 17.5N 113.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 12/1800Z 18.4N 113.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 13/0600Z...DISSIPATED

$$
Forecaster Gibbs/Hagen

[cycloneye]

Bye.

EP, 03, 2025061112, , BEST, 0, 162N, 1139W, 30, 1007, LO

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

[cycloneye]

Hasta la vista.

Post-Tropical Cyclone Cosme Discussion Number 13
NWS National Hurricane Center Miami FL EP032025
800 AM MST Wed Jun 11 2025

Drier mid-level air and stable atmospheric conditions have taken
their toll on Cosme. The system has been devoid of deep convection
for more than 12 hours, with only a swirl of low- to mid-level
clouds evident on satellite imagery. The initial intensity has
been lowered to 30 kt. Given the hostile environment and ongoing
lack of convection, Cosme is not expected to redevelop, and this
will be the final advisory.

The low is now moving toward the east-northeast at about 070/6 kt.
Global model guidance indicates a gradual turn toward the
north-northeast later today, followed by a turn to the north on
Thursday, as the system steadily spins down and dissipates over the
next day or so.

For additional information on the remnant low please see High Seas
Forecasts issued by the National Weather Service, under AWIPS
header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at
ocean.weather.gov/shtml/NFDHSFEPI.php

FORECAST POSITIONS AND MAX WINDS

INIT 11/1500Z 16.4N 113.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 12/0000Z 17.0N 113.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 12/1200Z 17.8N 113.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
36H 13/0000Z...DISSIPATED

$$
Forecaster Kelly/Gibbs