ATL: GASTON - Post-Tropical - Discussion

[tolakram]

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=34&lon=-49&info=vis&zoom=2&width=1024&height=768&type=Animation&quality=92&palette=ir1.pal&numframes=10&mapcolor=gray&map=none

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 36
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST WED AUG 31 2016

The satellite appearance of Gaston has degraded somewhat during the
past few hours, with a slightly cooler eye noted. A blend of the
latest Dvorak estimates suggest an initial wind speed of 100 kt for
this advisory. Only a slow weakening is anticipated over the next
couple of days while the hurricane moves over gradually cooling
waters in moderate shear conditions. Almost all of the guidance
show Gaston near hurricane strength in a couple of days as it
approaches the Azores. The latest NHC intensity forecast is lower
than the previous one, and best fits the model consensus.

Gaston has begun to move faster toward the east-northeast, now at
about 13 kt. The hurricane should accelerate in that general
direction over the next couple of days as it moves within the
mid-latitude westerlies. Most of the models have this system in
the vicinity of the Azores in about 2 days, and the official
forecast will continue to show this solution.

A hurricane or tropical storm watch will likely be issued for the
central or western Azores this afternoon.


FORECAST POSITIONS AND MAX WINDS

INIT 31/1500Z 34.0N 48.6W 100 KT 115 MPH
12H 01/0000Z 35.2N 46.1W 95 KT 110 MPH
24H 01/1200Z 36.9N 41.7W 85 KT 100 MPH
36H 02/0000Z 38.0N 36.8W 75 KT 85 MPH
48H 02/1200Z 38.8N 32.2W 60 KT 70 MPH
72H 03/1200Z 40.0N 24.5W 40 KT 45 MPH
96H 04/1200Z 43.0N 18.0W 30 KT 35 MPH...POST-TROPICAL
120H 05/1200Z...DISSIPATED

$$
Forecaster Blake

[1900hurricane]

I'd probably classify Gaston as an annular hurricane, despite the algorithm output in the SHIPS diagnostic. In fact, I'd say Gaston is easily more annular than Lester is right now.

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 37
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST WED AUG 31 2016

The satellite presentation of Gaston has gradually decayed today,
with the eye becoming more ragged in infrared imagery. The initial
intensity estimate is 90 kt based on a blend of the latest Dvorak
Final-T and CI numbers from TAFB and SAB. Steady weakening is
expected during the next few days while SSTs decrease steadily along
the forecast track and the shear increases above 20 kt by 48 hours.
The new NHC intensity forecast has been adjusted downward and is
close to the latest intensity model consensus, and now shows Gaston
weakening to a tropical storm as it approaches the Azores on Friday.
Gaston should lose tropical characteristics by 72 hours and
dissipate by 96 hours as shown by the global models.

The initial motion estimate is 055/16, and Gaston is expected to
move east-northeastward to eastward in the mid-latitude westerlies
through dissipation. The NHC track forecast is a little north of
the previous one and is along the middle of the guidance envelope
but faster than the TVCN consensus, trending toward the faster FSU
Superensemble.

Based on the new forecast, a tropical storm watch has been issued
for portions of the western and central Azores.

FORECAST POSITIONS AND MAX WINDS

INIT 31/2100Z 35.0N 46.9W 90 KT 105 MPH
12H 01/0600Z 36.3N 44.0W 85 KT 100 MPH
24H 01/1800Z 37.7N 39.5W 75 KT 85 MPH
36H 02/0600Z 38.5N 34.8W 65 KT 75 MPH
48H 02/1800Z 39.0N 30.8W 55 KT 65 MPH
72H 03/1800Z 41.0N 25.0W 35 KT 40 MPH...POST-TROPICAL
96H 04/1800Z...DISSIPATED

$$
Forecaster Brennan

[RL3AO]

Gaston is finally running into a solid jet streak. However, that eastern jet streak may have helped it a bit during the past day in terms of creating a solid upper level divergent pattern.

With low SSTs and another approaching jet streak (and Gaston being in the sinking part of jet), we should see it lose tropical characteristics rather quickly.

[tolakram]

 https://twitter.com/philklotzbach/status/771120284518617088

[tolakram]

IR

still hanging on.

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=55&lon=-46&info=ir&zoom=2&width=1024&height=768&type=Animation&quality=92&palette=ir2.pal&numframes=15&mapcolor=gray&map=none

[cycloneye]

BULLETIN
HURRICANE GASTON ADVISORY NUMBER 38
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST WED AUG 31 2016

...TROPICAL STORM CONDITIONS POSSIBLE OVER THE WESTERN AND
CENTRAL AZORES ON FRIDAY...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...36.0N 45.4W
ABOUT 935 MI...1500 KM W OF FAIAL ISLAND IN THE CENTRAL AZORES
ABOUT 1020 MI...1640 KM W OF LAJES AIR BASE IN THE AZORES
MAXIMUM SUSTAINED WINDS...105 MPH...165 KM/H
PRESENT MOVEMENT...NE OR 55 DEGREES AT 20 MPH...31 KM/H
MINIMUM CENTRAL PRESSURE...970 MB...28.65 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Watch is in effect for...
* Flores and Corvo in the western Azores
* Faial, Pico, Graciosa, Sao Jorge, and Terceira in the central
Azores

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.

For storm information specific to your area, please monitor
products issued by your national meteorological service.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
At 1100 PM AST (0300 UTC), the center of Hurricane Gaston was
located near latitude 36.0 North, longitude 45.4 West. Gaston is
moving toward the northeast near 20 mph (31 km/h). A turn toward
the east-northeast with an increase in forward speed is expected
during the next day or so. On the forecast track, the center of
Gaston will move near the western and central Azores on Friday.

Maximum sustained winds remain near 105 mph (165 km/h) with higher
gusts. Weakening is forecast during the next 48 hours, and Gaston
is expected to lose hurricane intensity by early Friday before it
reaches the western Azores.

Hurricane-force winds extend outward up to 45 miles (75 km) from the
center, and tropical-storm-force winds extend outward up to 175
miles (280 km).

The estimated minimum central pressure is 970 mb (28.65 inches).


HAZARDS AFFECTING LAND
----------------------
WIND: Tropical storm conditions are possible in the western and
central Azores on Friday.


NEXT ADVISORY
-------------
Next intermediate advisory at 200 AM AST.
Next complete advisory at 500 AM AST.

$$
Forecaster Berg

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 39
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 AM AST THU SEP 01 2016

Gaston has weakened a little overnight. The cloud pattern has lost
some organization with the convection more asymmetric and not quite
as deep as it was several hours ago. The Dvorak CI-numbers have
decreased to 4.5/77 kt from both TAFB and SAB, and the initial wind
speed is lowered to 80 kt based on that data. Gaston is expected to
cross the 26 deg C isotherm later today while it remains in an
environment of moderate southwesterly shear. These conditions
should cause steady weakening, and Gaston will likely fall below
hurricane strength by tonight. Continued weakening is forecast
when the cyclone moves near the Azores on Friday. The NHC intensity
forecast is in best agreement with the intensity model consensus.

The hurricane is moving quickly east-northeastward about 17 kt. This
general motion is expected to continue during the next day while
Gaston remains embedded in the mid-latitude westerlies. A decrease
in forward speed is predicted after that time due to the approach of
a large extratropical low. Gaston will likely be absorbed by the
extratropical low in about 3 days. The NHC track forecast lies near
the middle of the tightly-packed models.

Based on the current forecast, the Azores Meteorological Service has
issued a Tropical Storm Warning for the western-most islands of
Flores and Corvo.

FORECAST POSITIONS AND MAX WINDS

INIT 01/0900Z 36.8N 43.3W 80 KT 90 MPH
12H 01/1800Z 37.9N 39.9W 70 KT 80 MPH
24H 02/0600Z 38.7N 35.4W 60 KT 70 MPH
36H 02/1800Z 39.2N 31.8W 50 KT 60 MPH
48H 03/0600Z 40.0N 29.0W 40 KT 45 MPH
72H 04/0600Z...DISSIPATED

$$
Forecaster Cangialosi

[tolakram]

Visible

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=60&lon=-40&info=vis&zoom=1&width=1024&height=768&type=Animation&quality=92&palette=ir1.pal&numframes=5&mapcolor=gray&map=none

[Kazmit]

Looking a bit more ragged, like Alex . It shouldn't do much to the Azores, and Gaston won't be a fish spinner after all.

[Kazmit]

An ACE of 22.2 so far. Impressive.

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 40
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST THU SEP 01 2016

Despite a degraded satellite presentation, a 1302 UTC ASCAT-B pass
over Gaston showed a large area of hurricane force winds southeast
of the center and peak winds of 75 kt, and that will serve as the
initial intensity for this advisory. Weakening is forecast as
Gaston moves across the 26C SST isotherm later today and the
vertical shear is expected to increase to 20-30 kt by 48 hours.
Gaston should fall below hurricane strength tonight and gradually
lose tropical characteristics by 48 hours. The low is forecast to
dissipate by 72 hours, as shown in the global models. The NHC
intensity forecast is close to the new IVCN intensity consensus aid.

The hurricane is moving quickly east-northeastward, 070/21. Gaston
will continue moving generally east-northeastward within the mid-
latitude westerlies through dissipation. The new NHC forecast is
near the middle of the guidance envelope and the multi-model
consensus TVCN.

Based on the current forecast, the Azores Meteorological Service has
issued a Tropical Storm Warning for the islands of Faial, Pico,
Graciosa, Sao Jorge, and Terceira in the central Azores.

FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 37.6N 40.6W 75 KT 85 MPH
12H 02/0000Z 38.4N 37.1W 65 KT 75 MPH
24H 02/1200Z 39.1N 32.8W 55 KT 65 MPH
36H 03/0000Z 39.7N 29.8W 45 KT 50 MPH
48H 03/1200Z 41.0N 26.5W 35 KT 40 MPH...POST-TROPICAL
72H 04/1200Z...DISSIPATED

$$
Forecaster Brennan

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 41
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST THU SEP 01 2016

The eye of Gaston is no longer visible in geostationary imagery,
which shows the coldest convective tops are located west and north
of the center. Dvorak classifications have decreased to T3.5/4.5
from TAFB and T3.0/4.0 from SAB. Based on the winds seen in the
earlier ASCAT data, the initial intensity is lowered conservatively
to 70 kt for this advisory. Steady weakening is forecast as Gaston
is moving over waters below 26C and in an environment of 20-30 kt of
southwesterly shear. The NHC forecast is a little lower than the
previous one following the trend of all the guidance. Gaston should
become post-tropical in about 48 hours and dissipate shortly
thereafter.

The hurricane has accelerated east-northeastward this afternoon,
with an initial motion estimate of 075/25. The track model guidance
is in good agreement showing Gaston continuing east-northeastward
with a decrease in forward speed as the system weakens and decouples
from the mid-level flow. The new NHC track forecast is basically an
update of the previous one and is very close to the latest multi-
model consensus aid TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 38.3N 37.5W 70 KT 80 MPH
12H 02/0600Z 38.9N 34.5W 60 KT 70 MPH
24H 02/1800Z 39.5N 30.9W 50 KT 60 MPH
36H 03/0600Z 40.3N 27.9W 40 KT 45 MPH
48H 03/1800Z 41.6N 25.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 04/1800Z...DISSIPATED

$$
Forecaster Brennan

[cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 42
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST THU SEP 01 2016

The low-level center of Gaston is becoming exposed in infrared
satellite imagery, with about 25 kt of westerly shear pushing the
deep convection out ahead of the cyclone. Dvorak CI numbers remain
4.5/77 kt from TAFB and 4.0/65 kt from SAB, while the objective ADT
has dropped well into tropical storm territory. The initial winds
are only lowered to 65 kt to allow for a gradual spin down of the
circulation, but this estimate could be generous. Due to
progressively colder sea surface temperatures and persistent shear,
continued weakening is forecast. Gaston could lose its deep
convection in about 36 hours after it has passed the Azores, and
that's when it is expected to become post-tropical. Dissipation is
still forecast by day 3. The NHC intensity forecast is an update of
the previous one and most closely follows the LGEM.

Now that Gaston's center is exposed, there is more confidence in
the initial motion (075/20 kt). Gaston is expected to move
eastward or east-northeastward at a slower forward speed near the
western and central Azores during the next 36 hours. After that
time, the shallow remnant low should turn northeastward ahead of an
approaching cold front. The track guidance remains in good
agreement, and the NHC forecast is close to the TVCN multi-model
consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 02/0300Z 38.3N 36.0W 65 KT 75 MPH
12H 02/1200Z 38.8N 33.0W 55 KT 65 MPH
24H 03/0000Z 39.4N 29.8W 45 KT 50 MPH
36H 03/1200Z 40.6N 27.0W 35 KT 40 MPH...POST-TROPICAL
48H 04/0000Z 42.7N 23.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 05/0000Z...DISSIPATED

$$
Forecaster Berg

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 44
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST FRI SEP 02 2016

Data from a recent ASCAT overpass indicate that the storm
is a little stronger than previously estimated. The advisory
intensity is set to 60 kt based on the scatterometer winds.
Vertical shear over the system is currently around 20 kt and is
forecast to increase to near 30 kt within the next day or so, and
the cyclone will be moving over progressively cooler waters.
Weakening is forecast in agreement with the IVCN intensity model
consensus. Gaston should weaken to a remnant low before becoming
absorbed by a frontal system in 48 hours or less.

Based on the scatterometer data and conventional geostationary
satellite fixes, the motion is east-northeastward or 070/16.
Gaston should continue on an east-northeastward track, following the
flow on the south side of the mid-latitude westerlies, until
dissipation. The official track forecast is close to the
multi-model consensus TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 39.1N 32.0W 60 KT 70 MPH
12H 03/0000Z 39.5N 29.8W 45 KT 50 MPH
24H 03/1200Z 40.7N 27.0W 35 KT 40 MPH
36H 04/0000Z 42.5N 24.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 04/1200Z...DISSIPATED

$$
Forecaster Pasch

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 45
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST FRI SEP 02 2016

Gaston is practically devoid of deep convection, and it is assumed
that a significant spindown has occurred today. Under this
assumption, the advisory intensity is set at 45 kt which is
in agreement with a Dvorak Current Intensity number from TAFB.
Since the cyclone will be moving over the colder waters to the
north of the Azores and through an environment of strong shear, the
forecast calls for the system to degenerate into a remnant low in
24 hours, and this event may occur even sooner than that.

Microwave and geostationary satellite fixes, along with
observations from Flores in the Azores, indicate that the motion is
around 070/15 kt. Gaston should curve gradually toward the
northeast, ahead of a broad trough in the mid-latitude westerlies,
until dissipation. The official track forecast is very close to the
dynamical model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 02/2100Z 39.6N 30.4W 45 KT 50 MPH
12H 03/0600Z 40.3N 28.1W 35 KT 40 MPH
24H 03/1800Z 42.1N 25.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 04/0600Z 44.3N 21.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 04/1800Z...DISSIPATED

$$
Forecaster Pasch

[galaxy401]

000
WTNT42 KNHC 030238
TCDAT2

TROPICAL STORM GASTON DISCUSSION NUMBER 46
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST FRI SEP 02 2016

A 2222 UTC ASCAT-B pass indicated that Gaston was producing maximum
winds of 30-35 kt in its southeastern quadrant. The initial
intensity is therefore lowered to 35 kt, but Gaston won't be a
tropical storm for much longer. The last bit of deep convection
dissipated around 1800 UTC, so the cyclone is likely to be declared
post-tropical Saturday morning. The remnant low is likely to
maintain 30-kt winds until it dissipates in 36 hours, based on
guidance from the global models.

The initial motion is 070/14 kt. The remnant low is expected to
turn northeastward and accelerate away from the Azores during the
next 24 hours ahead of an approaching cold front. The track models
agree on this scenario, and the NHC forecast remains close to the
TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 40.1N 28.7W 35 KT 40 MPH
12H 03/1200Z 41.1N 26.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 04/0000Z 43.3N 23.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 04/1200Z...DISSIPATED

$$
Forecaster Berg

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 46
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST FRI SEP 02 2016

A 2222 UTC ASCAT-B pass indicated that Gaston was producing maximum
winds of 30-35 kt in its southeastern quadrant. The initial
intensity is therefore lowered to 35 kt, but Gaston won't be a
tropical storm for much longer. The last bit of deep convection
dissipated around 1800 UTC, so the cyclone is likely to be declared
post-tropical Saturday morning. The remnant low is likely to
maintain 30-kt winds until it dissipates in 36 hours, based on
guidance from the global models.

The initial motion is 070/14 kt. The remnant low is expected to
turn northeastward and accelerate away from the Azores during the
next 24 hours ahead of an approaching cold front. The track models
agree on this scenario, and the NHC forecast remains close to the
TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 40.1N 28.7W 35 KT 40 MPH
12H 03/1200Z 41.1N 26.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 04/0000Z 43.3N 23.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 04/1200Z...DISSIPATED

$$
Forecaster Berg

[cycloneye]

POST-TROPICAL CYCLONE GASTON DISCUSSION NUMBER 47
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 AM AST SAT SEP 03 2016

Gaston has been devoid of deep convection for more than 12 hours,
and is now a swirl of stratocumulus clouds. Since the cyclone is
moving over 22-23 deg C waters and embedded in northwesterly shear
of about 35 kt, the likelihood that any new convection would reform
is slim. Given this, Gaston is being declared a post-tropical
remnant low on this advisory. Without any new convection
redeveloping the vortex is expected to spin down rather quickly, and
global models show Gaston opening up into a trough in about 18
hours.

The initial motion estimate is 065/15. The post-tropical cyclone
should accelerate east-northeastward at the base of the mid-
latitude westerlies today, and then turn northeastward ahead of a
trough digging over Atlantic Canada prior to dissipation on Sunday.

This is the last advisory issued on Gaston by the National
Hurricane Center. Additional information on this system can be
found in High Seas Forecasts issued by Meteo France under WMO header
FQNT50 LFPW and available on the web at
http://www.meteofrance.com/previsions-m ... e/bulletin.


FORECAST POSITIONS AND MAX WINDS

INIT 03/0900Z 40.5N 26.9W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 03/1800Z 42.4N 24.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 04/0600Z...DISSIPATED

$$
Forecaster Kimberlain