ATL: GASTON - Advisories

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ATL: GASTON - Advisories

#1 Postby AJC3 » Tue Sep 20, 2022 4:31 pm

BULLETIN
Tropical Depression Eight Advisory Number 1
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
1100 AM AST Tue Sep 20 2022

...EIGHTH TROPICAL DEPRESSION OF THE SEASON FORMS OVER THE CENTRAL
ATLANTIC...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...32.8N 45.7W
ABOUT 1110 MI...1785 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...N OR 5 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...1013 MB...29.92 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.

Interests in the Azores should monitor the progress of the system.


Tropical Depression Eight Discussion Number 1
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
1100 AM AST Tue Sep 20 2022

Geostationary and microwave satellite data indicate that the system
that NHC has been monitoring over the central Atlantic has developed
a well-defined center and organized deep convection, and now meets
the definition of a tropical cyclone. The initial intensity is
estimated to be 30 kt based on a partial ASCAT pass that showed peak
winds in the 25-30 kt range. The low-level center is estimated to
be on the southern side of the main area of deep convection.

The depression is currently moving northward at 9 kt on the western
side of a subtropical ridge. A faster motion to the northeast is
expected on Wednesday when the system reaches the northwestern
periphery of the ridge, followed by a turn to the east. By the end
of the week, however, the depression is expected to stall in weak
steering currents as high pressure builds near and to the north of
the cyclone. Over the weekend, the depression is expected to turn
northwestward and increase its forward speed as Fiona tracks well to
the west of this system. The models are in fair agreement, but
there is some cross-track spread by the end of the period with the
GFS showing the fastest solution and ECMWF the slowest. The NHC
track forecast lies close to the various consensus models.

The depression is currently over relatively warm water, in a region
of upper-level diffluence within a somewhat favorable moist
environment. These factors should allow the system to strengthen
slowly during the next couple of days. However, after that time,
much cooler SSTs, drier air, and an increase in westerly shear
should end the strengthening trend. The system is expected to
become extratropical over the weekend when it moves over SSTs just
above 20C. The NHC intensity forecast lies a little lower than
HCCA and IVCN consensus models.

Interests in the Azores should monitor forecasts of the depression.

FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 32.8N 45.7W 30 KT 35 MPH
12H 21/0000Z 34.6N 45.0W 35 KT 40 MPH
24H 21/1200Z 36.7N 43.2W 40 KT 45 MPH
36H 22/0000Z 38.2N 40.6W 45 KT 50 MPH
48H 22/1200Z 39.2N 37.8W 50 KT 60 MPH
60H 23/0000Z 39.7N 35.3W 50 KT 60 MPH
72H 23/1200Z 39.8N 33.7W 50 KT 60 MPH
96H 24/1200Z 40.1N 33.7W 50 KT 60 MPH
120H 25/1200Z 42.4N 36.9W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Pereira/Montgomery
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Re: ATL: GASTON - Advisories

#2 Postby AJC3 » Tue Sep 20, 2022 4:32 pm

BULLETIN
Tropical Storm Gaston Advisory Number 2
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
900 PM GMT Tue Sep 20 2022

...DEPRESSION STRENGTHENS INTO TROPICAL STORM GASTON...


SUMMARY OF 900 PM GMT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...34.7N 44.4W
ABOUT 990 MI...1595 KM W OF THE AZORES
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NNE OR 20 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1009 MB...29.80 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.

Interests in the Azores should monitor the progress of the system.


Tropical Storm Gaston Discussion Number 2
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
900 PM GMT Tue Sep 20 2022

Satellite images indicate that deep convection is persisting near
and to the north of the center of the cyclone during the past
several hours. Drifting buoy 44857 recently reported a minimum
pressure of 1009 mb near the center of the low, which is a 8 mb
decrease from earlier today. An ASCAT-C pass from several hours ago
showed maximum winds of about 35 kt in the northeast and northwest
quadrants. Based on that data, the initial intensity is increased
to 35 kt, making the system Tropical Storm Gaston.

Gaston has turned north-northeastward and is moving a little faster
than before. The initial motion estimate is 020/15 kt. A turn to
the east is expected in a couple of days when the tropical storm
moves along the northern periphery of a subtropical ridge. By the
end of the week, however, Gaston is expected to stall to the west of
the Azores in weak steering currents as high pressure builds near
and to the north of the cyclone. After that time, a turn to the
northwest or north is expected as Gaston moves in the flow between
Hurricane Fiona and the ridge. The models have trended a little
faster this cycle, and the NHC track forecast has been adjusted
accordingly.

Gaston is currently moving over relatively warm water, in a region
of upper-level diffluence within a somewhat favorable moist
environment. These factors should allow the system to strengthen
slowly during the next day or two. However, after that time,
much cooler SSTs, drier air, and an increase in westerly shear
should end the strengthening trend. The system is expected to
become extratropical on Saturday when it moves over SSTs just
above 20C and merges with a mid- to upper-level trough. The NHC
intensity forecast is about the same as the previous one and near
the middle of the guidance envelope.

Interests in the Azores should monitor the forecast for Gaston.


FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 34.7N 44.4W 35 KT 40 MPH
12H 21/0600Z 36.5N 43.3W 40 KT 45 MPH
24H 21/1800Z 38.3N 40.9W 45 KT 50 MPH
36H 22/0600Z 39.4N 38.0W 50 KT 60 MPH
48H 22/1800Z 40.1N 35.3W 50 KT 60 MPH
60H 23/0600Z 40.3N 33.1W 50 KT 60 MPH
72H 23/1800Z 40.4N 32.5W 50 KT 60 MPH
96H 24/1800Z 41.0N 32.5W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 25/1800Z 44.0N 35.3W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Kebede
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Re: ATL: GASTON - Advisories

#3 Postby cycloneye » Tue Sep 20, 2022 10:07 pm

BULLETIN
Tropical Storm Gaston Advisory Number 3
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Wed Sep 21 2022

...GASTON STRENGTHENS SLIGHTLY OVER THE CENTRAL NORTH ATLANTIC...


SUMMARY OF 300 AM GMT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...36.2N 43.6W
ABOUT 920 MI...1485 KM W OF THE AZORES
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...NNE OR 20 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES



Tropical Storm Gaston Discussion Number 3
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Wed Sep 21 2022

The satellite presentation of Gaston has improved slightly since
the previous advisory, with deep convection persisting over the
low-level circulation center. The latest current intensity
estimates reflect what has been seen in the satellite imagery, with
TAFB and SAB coming in at 45 knots, while the ADT and AiDT values
from UW-CIMSS showing 35 knots and 46 knots respectively. Based on
a blend of these data along with the improved satellite appearance,
the initial intensity has been raised to 45 knots.

Gaston continues on a path toward the north-northeast,
with the initial motion estimated to be 020/16 kt. A turn to
northeast is expected today, followed by a turn to the east by
Thursday as the tropical storm moves along the the northern
periphery of a subtropical ridge. By late this week, Gaston is
expected to stall to the west of the Azores in weak steering
currents as a mid-level ridge builds to the north of cyclone. A turn
to the northwest or north is expected over the weekend as Gaston
moves in the steering flow between Hurricane Fiona to the west and
the building mid-level ridge to the east. The latest NHC track
forecast has changed little and lies very close to the previous
advisory track, and closely follows the consensus track guidance.

The period for additional intensification is quickly closing, as
Gaston is moving over the 26C isotherm, and will move over
progressively cooler water through the remainder of the forecast
period. Additionally, the impact of the vertical wind shear will
increase in a couple days as the tropical cyclone stalls out while
westerly shear holds in the 25 to 30 knot range. As a result, the
intensity forecast calls for slight strengthening today, followed by
little change in strength for another day or so after that. The
combination of cool SSTs, dry mid-level air, and increasing vertical
wind shear should then lead to slow weakening through the remainder
of the week. The latest NHC was adjusted upward through the first 24
hours to account for the strengthening which has already occurred,
with only minor adjustments made through the remainder of the
forecast period, closely following the consensus intensity aids.

Interests in the Azores should continue to monitor the forecast for
Gaston.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0300Z 36.2N 43.6W 45 KT 50 MPH
12H 21/1200Z 37.8N 41.9W 50 KT 60 MPH
24H 22/0000Z 39.3N 39.1W 50 KT 60 MPH
36H 22/1200Z 40.2N 36.0W 50 KT 60 MPH
48H 23/0000Z 40.4N 32.9W 45 KT 50 MPH
60H 23/1200Z 40.4N 31.9W 45 KT 50 MPH
72H 24/0000Z 40.4N 31.9W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 25/0000Z 41.5N 33.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 26/0000Z 43.5N 35.2W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster D. Zelinsky/Jelsema
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Re: ATL: GASTON - Advisories

#4 Postby cycloneye » Wed Sep 21, 2022 4:35 am

Tropical Storm Gaston Discussion Number 4
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Wed Sep 21 2022

Gaston has continued to improve on satellite imagery overnight.
Curved bands can be seen rotating fully around the southwestern
side
of the tropical cyclone with a warm spot occasionally apparent near
where the center is. I was somewhat skeptical that this structure
was indicative of a formative inner core, but a helpful GMI
microwave pass at 0407 UTC revealed this was no illusion, with a
nearly closed ring of convection on both 89 and 37 GHz channels.
Subjective Dvorak classifications from SAB were T3.0/45-kt and
TAFB T3.5/55-kt. Given the improvement in structure tonight, the
winds have been increased to 55-kt this advisory.

Gaston continues to move to the north-northeast at 025/16 kt. A
turn
north northeastward is expected later today followed by a more
eastward motion by Thursday. By the latter part of this week,
Gaston
is forecast to come to near screeching halt to the west of the
Azores in weak steering currents as a mid-level ridge builds
northward, related to Fiona's downstream diabatic induced ridging.
A
turn to the northwest or north is expected over the weekend as
Gaston moves in the steering flow between Hurricane Fiona to the
west and the building mid-level ridge to the east. The latest NHC
track forecast has changed little and lies very close to the
previous advisory track.

Based on the current structure, Gaston might be able to intensify a
bit more today. However as Gaston slows down the westerly
upper-level flow the storm is embedded will likely cause the
structure to deteriorate, with both the GFS and ECMWF simulated
satellite imagery suggesting the convection could de-couple from
the storm in about 48-60 hours. Thus, the latest forecast shows
weakening during this time period, and Gaston could become a
post-tropical extratropical cyclone as soon as 72 hours. The latest
NHC intensity forecast is a bit higher, owing to the initial
intensity, but remains fairly close to the previous forecast after
60 hours.

Interests in the Azores should continue to monitor the forecast for
Gaston.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 37.5N 42.6W 55 KT 65 MPH
12H 21/1800Z 38.8N 40.6W 60 KT 70 MPH
24H 22/0600Z 40.1N 37.7W 60 KT 70 MPH
36H 22/1800Z 40.8N 34.7W 55 KT 65 MPH
48H 23/0600Z 40.9N 32.6W 50 KT 60 MPH
60H 23/1800Z 40.8N 31.4W 45 KT 50 MPH
72H 24/0600Z 41.3N 31.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 25/0600Z 42.6N 33.7W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 26/0600Z 44.3N 35.2W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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Re: ATL: GASTON - Advisories

#5 Postby cycloneye » Wed Sep 21, 2022 9:39 am

Tropical Storm Gaston Discussion Number 5
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
300 PM GMT Wed Sep 21 2022

Satellite images indicate that Gaston continues to produce
convection that has become increasingly symmetric around the center.
In addition, there is a broken band of thunderstorms on the eastern
side of the system. The Dvorak classifications from TAFB and SAB
were both 3.5/55 kt. A recent ASCAT-B pass indicate that Gaston has
a relatively symmetric wind field with maximum winds in the 45-50 kt
range. Based on this data, the initial intensity remains 55 kt for
this advisory. It is worth mentioning that satellite data indicate
that Gaston is not purely tropical and is likely a hybrid system
gaining energy from baroclinic sources.

Gaston continues to track northeastward over the north-central
Atlantic, with the latest initial motion estimated to be 035/14 kt.
Although there is no significant change to the forecast reasoning,
there is a modest amount of model spread in the details of the
future steering pattern. The NHC track is faster and a tad south of
the previous forecast, trending toward the latest consensus models.
Gaston is expected to turn to the east in a day or so when it moves
on the northern side of a subtropical ridge and then will likely
slow down considerably or completely stall near or just west of the
western Azores late this week. If the storm survives, a turn to the
north or northwest could occur over the weekend.

The storm could strengthen a little today given recent trends in
its convective development near and around the center. However,
weakening should begin on Thursday when Gaston moves over cooler
waters and into a region of drier air and slightly stronger
westerly vertical wind shear. An approaching mid-level trough
should aid in the system's transition to an extratropical cyclone
in a couple of days or so. The NHC intensity forecast lies near
the middle of the guidance envelope.

Interests in the Azores should continue to monitor the forecast for
Gaston. For additional information, see warnings and products
issued by the meteorological service in the Azores.


FORECAST POSITIONS AND MAX WINDS

INIT 21/1500Z 38.3N 41.3W 55 KT 65 MPH
12H 22/0000Z 39.5N 39.0W 60 KT 70 MPH
24H 22/1200Z 40.6N 35.6W 55 KT 65 MPH
36H 23/0000Z 40.9N 32.6W 55 KT 65 MPH
48H 23/1200Z 40.8N 30.7W 50 KT 60 MPH
60H 24/0000Z 40.5N 30.0W 50 KT 60 MPH...POST-TROP/EXTRATROP
72H 24/1200Z 40.0N 30.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 25/1200Z 41.2N 34.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 26/1200Z 42.5N 36.0W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Kong/Gallina

NNNN
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Re: ATL: GASTON - Advisories

#6 Postby cycloneye » Wed Sep 21, 2022 4:03 pm

Tropical Storm Gaston Discussion Number 6
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
900 PM GMT Wed Sep 21 2022

There has been little change associated with Gaston during the past
several hours. The system continues to produce an area of deep
convection near the center and exhibits well-defined outflow over
the western semicircle. However, drier air is entraining into
the eastern portion of the circulation. The Dvorak CI-numbers from
TAFB and SAB continue to support an initial intensity of 55 kt.

Gaston continues to track northeastward over the north-central
Atlantic, with the latest initial motion estimated to be 045/12 kt.
Although there is no significant change to the forecast reasoning,
there is a considerable amount of model spread in the details of the
future steering pattern. An amplifying ridge associated with Fiona
is expected to trap Gaston's circulation late this week and this
weekend. This could result in a clockwise loop and an eventual
turn westward. The new NHC track forecast is a little to the south
and faster than the previous one, trending toward the latest
consensus models.

It appears that the opportunity for strengthening has ended. A slow
weakening trend should begin in the next day or so when Gaston moves
over cooler waters and into a region of drier air and slightly
stronger westerly vertical wind shear. An approaching mid-level
trough should aid in the system's transition to an extratropical
cyclone in a couple of days or so. The NHC intensity forecast
remains near the middle of the guidance envelope.

Interests in the Azores should continue to monitor the forecast for
Gaston. For additional information, see warnings and products
issued by the meteorological service in the Azores.


FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 39.0N 40.0W 55 KT 65 MPH
12H 22/0600Z 40.0N 37.4W 55 KT 65 MPH
24H 22/1800Z 40.8N 33.9W 55 KT 65 MPH
36H 23/0600Z 40.9N 31.2W 50 KT 60 MPH
48H 23/1800Z 40.4N 30.0W 50 KT 60 MPH
60H 24/0600Z 39.8N 30.1W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 24/1800Z 39.6N 31.1W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 25/1800Z 40.3N 34.7W 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 26/1800Z 41.0N 37.0W 35 KT 40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Wegman/Carbin
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Re: ATL: GASTON - Advisories

#7 Postby cycloneye » Thu Sep 22, 2022 3:44 am

BULLETIN
Tropical Storm Gaston Advisory Number 8
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Thu Sep 22 2022

...GASTON HEADING TOWARD THE WESTERNMOST AZORES ISLANDS...
...TROPICAL STORM WARNING ISSUED FOR THE WESTERN AND CENTRAL
ISLANDS...


SUMMARY OF 900 AM GMT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...40.3N 35.4W
ABOUT 375 MI...605 KM WNW OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...ENE OR 70 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES


Tropical Storm Gaston Discussion Number 8
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Thu Sep 22 2022

GOES-16 Enhanced BD-curve infrared imagery and a recent GMI
microwave pass showed that Gaston had maintained a deep convective
inner core during the past several hours. Subsequently, a
primary curved band with -66C cloud tops has developed in the
western semicircle. A compromise of the subjective satellite
intensity estimates from TAFB and SAB, along with a UW-CIMSS AiDT
estimated, yields an initial intensity of 55 kt for this advisory.

Although the intensity guidance agrees that Gaston will commence a
slow weakening trend soon, predicting when Gaston will become a
post-tropical cyclone or if it transitions into an extratropical low
is problematic. The GFS and ECMWF-SHIPS statistical diagnostics
indicate that Gaston will complete extratropical transition in just
6 hours, which appears unrealistic. On the other hand, the FSU
Cyclone phase forecast for the GFS and UKMET suggest that the system
will maintain a symmetric lower-tropospheric warm core while moving
south of the upper westerlies on Friday. The latter scenario seems
more reasonable since Gaston is sustaining inner core convection and
the wind flow aloft becomes a bit more diffluent as it approaches
the Azores Islands. Afterwards, the global simulated IR forecasts
show Gaston becoming a post-tropical cyclone (loss of tropical cloud
pattern characteristics) in 48 hours due to sub-24C SSTs, an
increasing stable/dry surrounding atmosphere, and strong northerly
shear. The NHC forecast is based on the above mentioned global
model guidance and shows Gaston becoming a post-tropical cyclone on
Saturday.

Gaston's initial motion is estimated to be east-northeastward, or
070/15 kt. The are no significant changes to the previous track
forecast or synoptic reasoning. Gaston is expected to move
east-northeastward to eastward through Friday morning.
Afterward, the Azores high is predicted to strengthen and cause
Gaston to gradually turn southward. Beyond 48 hours, the
global and hurricane models indicate that the cyclone will turn
toward the west-southwest to west in response to the aforementioned
high-pressure building to the north and northeast of the system.
The NHC forecast is based on this scenario and lies between the TVCA
and HCCA consensus models.

Because the latest forecast track of Gaston brings the cyclone near
or over the western and central Azores islands before becoming
post-tropical, The Azores Meteorological Service has issued a
Tropical Storm Warning for their western and central island chains.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0900Z 40.3N 35.4W 55 KT 65 MPH
12H 22/1800Z 40.9N 32.6W 55 KT 65 MPH
24H 23/0600Z 40.7N 30.0W 55 KT 65 MPH
36H 23/1800Z 39.8N 28.8W 50 KT 60 MPH
48H 24/0600Z 38.9N 29.1W 45 KT 50 MPH...POST-TROPICAL
60H 24/1800Z 38.5N 30.4W 45 KT 50 MPH...POST-TROPICAL
72H 25/0600Z 38.6N 32.2W 40 KT 45 MPH...POST-TROPICAL
96H 26/0600Z 38.2N 35.9W 35 KT 40 MPH...POST-TROPICAL
120H 27/0600Z 37.1N 39.8W 30 KT 35 MPH...POST-TROPICAL

$$
Forecaster Roberts
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Re: ATL: GASTON - Advisories

#8 Postby cycloneye » Thu Sep 22, 2022 9:58 am

BULLETIN
Tropical Storm Gaston Advisory Number 9
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
300 PM GMT Thu Sep 22 2022

...GASTON MAINTAINING ITS STRENGTH...
...TROPICAL STORM CONDITIONS EXPECTED TO BEGIN IN THE
AZORES TONIGHT...


SUMMARY OF 300 PM GMT...1500 UTC...INFORMATION
----------------------------------------------
LOCATION...40.9N 33.8W
ABOUT 315 MI...505 KM WNW OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...ENE OR 65 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES



Tropical Storm Gaston Discussion Number 9
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
300 PM GMT Thu Sep 22 2022

Gaston has been relatively steady in strength during the past
several hours. Recent visible and microwave images indicate that
the storm has a fairly well-defined inner core. However, an SSMI
overpass shows that the system is tilted in the vertical due to
west-southwesterly shear. The 12Z Dvorak estimates from TAFB and
SAB were unchanged, and the initial intensity remains 55 kt at the
high end of the classifications. An ASCAT-B pass showed peak winds
of around 45 kt in the southeastern quadrant and given the low bias
of the instrument for these cases, this data also supports the
55-kt initial wind speed. The 34-kt wind radii has been expanded
outward based on the scatterometer data.

The storm is still moving east-northeastward at 18 kt on the
northwestern periphery of a subtropical ridge. A turn to the east
and a reduction in forward speed are expected tonight, followed by a
clockwise loop near or over the central and western Azores on Friday
and Saturday as the storm moves on the south side of another ridge.
The models have generally changed little this cycle, and the NHC
track forecast is very similar to the previous one.

Despite moderate to strong shear, relatively dry air, and cool
SSTs, Gaston has been maintaining its strength. Given that these
conditions are only expected to gradually worsen for the system, a
slow weakening trend seems likely. The models all show a similar
theme, and the NHC intensity forecast lies near the middle of the
guidance envelope. Gaston is expected to become post-tropical in a
couple of days when it merges with an approaching shortwave trough.

Key Messages:

1. Tropical storm conditions are expected to begin tonight in the
western Azores and will likely spread to the central Azores on
Friday.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores beginning tonight and continuing into Saturday.

FORECAST POSITIONS AND MAX WINDS

INIT 22/1500Z 40.9N 33.8W 55 KT 65 MPH
12H 23/0000Z 41.2N 31.2W 55 KT 65 MPH
24H 23/1200Z 40.7N 29.3W 55 KT 65 MPH
36H 24/0000Z 39.6N 29.0W 50 KT 60 MPH
48H 24/1200Z 38.9N 30.0W 50 KT 60 MPH...POST-TROPICAL
60H 25/0000Z 38.9N 31.7W 45 KT 50 MPH...POST-TROPICAL
72H 25/1200Z 39.1N 33.6W 45 KT 50 MPH...POST-TROPICAL
96H 26/1200Z 38.3N 37.2W 35 KT 40 MPH...POST-TROPICAL
120H 27/1200Z 37.2N 40.7W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Cangialosi/Weiss/Taylor
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Re: ATL: GASTON - Advisories

#9 Postby cycloneye » Thu Sep 22, 2022 3:55 pm

BULLETIN
Tropical Storm Gaston Advisory Number 10
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
900 PM GMT Thu Sep 22 2022

...GASTON APPROACHING THE WESTERN AZORES ISLANDS..
...TROPICAL STORM CONDITIONS EXPECTED TO BEGIN LATER TONIGHT...


SUMMARY OF 900 PM GMT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...41.1N 32.0W
ABOUT 245 MI...395 KM NW OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...ENE OR 70 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES




Tropical Storm Gaston Discussion Number 10
NWS National Hurricane Center Miami FL AL082022
Issued by the NWS Weather Prediction Center College Park MD
900 PM GMT Thu Sep 22 2022

Gaston is beginning to approach the Azores Islands. An observation
on Flores in the western Azores recently showed wind gusts to
tropical storm strength in an outer band of the storm. Satellite
images indicate that Gaston has been relatively steady in strength
through the day with deep convection persisting near the center and
strong outflow continuing in the northern semicircle. Since the
Dvorak estimates are unchanged, the initial intensity remains 55 kt
for this advisory.

The storm has slowed down slightly, with the latest initial motion
estimated to be east-northeastward at 15 kt. A turn to the east and
an additional reduction in forward speed are expected overnight,
followed by a clockwise loop near or over the central and western
Azores on Friday and Saturday as the storm moves on the south side
of a building ridge. The models have trended northward at days 4
and 5, and the NHC track forecast has been adjusted in that
direction for those time periods.

Despite moderate to strong shear, relatively dry air, and cool
SSTs, Gaston has been maintaining its strength. Given that these
conditions are only expected to gradually worsen for the system, a
slow weakening trend seems likely. The models all show a similar
theme, and the NHC intensity forecast lies near the middle of the
guidance envelope. Gaston is expected to become post-tropical on
Saturday when it merges with an approaching shortwave trough.

Key Messages:

1. Tropical storm conditions are expected to begin later tonight in
the western Azores and will likely spread to the central Azores on
Friday.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores beginning tonight and continuing into Saturday.
This rainfall may result in landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 22/2100Z 41.1N 32.0W 55 KT 65 MPH
12H 23/0600Z 40.9N 30.1W 55 KT 65 MPH
24H 23/1800Z 40.1N 29.2W 55 KT 65 MPH
36H 24/0600Z 39.2N 29.5W 50 KT 60 MPH
48H 24/1800Z 38.8N 30.9W 50 KT 60 MPH...POST-TROPICAL
60H 25/0600Z 39.1N 33.1W 50 KT 60 MPH...POST-TROPICAL
72H 25/1800Z 39.3N 35.0W 45 KT 50 MPH...POST-TROPICAL
96H 26/1800Z 39.3N 37.8W 35 KT 40 MPH...POST-TROPICAL
120H 27/1800Z 40.5N 40.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Cangialosi/Churchill/Hamrick
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Re: ATL: GASTON - Advisories

#10 Postby cycloneye » Thu Sep 22, 2022 9:40 pm

BULLETIN
Tropical Storm Gaston Advisory Number 11
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Fri Sep 23 2022

...TROPICAL STORM CONDITIONS AFFECTING PORTIONS OF THE
AZORES...


SUMMARY OF 300 AM GMT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...41.0N 31.0W
ABOUT 205 MI...330 KM NW OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...E OR 100 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES


Tropical Storm Gaston Discussion Number 11
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Fri Sep 23 2022

Gaston's cloud pattern is showing signs of disruption by westerly
shear with the center located near the western edge of the main
area of convection. This was confirmed by a recent scatterometer
overpass, which showed that the intensity was, somewhat
surprisingly, still near 55 kt. This intensity is also in
agreement with a Dvorak classification from TAFB, and so the
advisory's initial wind speed is held at that value.

The storm has continued to slow its forward speed, with the latest
initial motion estimated to be eastward at around 10 kt.
During the next day or so, Gaston is expected to move on a
clockwise loop along the southern side of a blocking mid-level
ridge. The official track forecast follows the multi-model
consensus prediction. This is fairly close to the previous NHC
forecast, except shifted a little northward in the latter part of
the period.

Gaston is expected to remain in an environment of dry air, over
relatively cool SSTs, and under the influence of strong westerly
shear for the next couple of days. These factors should lead to
gradual weakening and loss of tropical characteristics in 48 hours
or so. The official intensity forecast is similar to the previous
one and is close to the latest Decay-SHIPS prediction.


Key Messages:

1. Tropical storm conditions are occurring over portions of the
western Azores, and will likely spread to the central Azores later
today.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores today into Saturday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0300Z 41.0N 31.0W 55 KT 65 MPH
12H 23/1200Z 40.4N 29.4W 55 KT 65 MPH
24H 24/0000Z 39.3N 29.3W 50 KT 60 MPH
36H 24/1200Z 38.7N 30.4W 50 KT 60 MPH
48H 25/0000Z 38.9N 32.3W 50 KT 60 MPH...POST-TROPICAL
60H 25/1200Z 39.4N 34.4W 45 KT 50 MPH...POST-TROPICAL
72H 26/0000Z 39.8N 36.4W 40 KT 45 MPH...POST-TROPICAL
96H 27/0000Z 40.9N 38.0W 35 KT 40 MPH...POST-TROPICAL
120H 28/0000Z 41.5N 39.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Pasch
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Re: ATL: GASTON - Advisories

#11 Postby cycloneye » Fri Sep 23, 2022 3:55 am

BULLETIN
Tropical Storm Gaston Intermediate Advisory Number 11A
NWS National Hurricane Center Miami FL AL082022
600 AM GMT Fri Sep 23 2022

...TROPICAL STORM CONDITIONS AFFECTING THE WESTERNMOST AZORES
ISLANDS...


SUMMARY OF 600 AM GMT...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...40.8N 29.9W
ABOUT 165 MI...265 KM NNW OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...ESE OR 105 DEGREES AT 14 MPH...23 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES


Tropical Storm Gaston Discussion Number 12
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Fri Sep 23 2022

Gaston's cloud pattern has changed considerably in appearance
since yesterday. A tropical cyclone axisymmetric wind
field that is typically concentrated about the surface center has
transformed to a more asymmetric pattern with considerable
expansion to the northeast due to the brisk mid-latitude
westerlies and the sub-25C cool oceanic surface temperatures.
Involvement between Gaston and a major shortwave trough/baroclinic
zone noted in water vapor imagery and a recent AMSR2 microwave pass
has resulted in a delta rain shield north of the exposed surface
circulation. A subsequent polar jet finger is visible in imagery
northeast of the center, with possible warm seclusion development.
All these attributes may well be leading to post-tropical cyclone
transition. The subjective satellite intensity estimates and a
recent UW-CIMSS SATCON analysis yield an initial intensity of 50 kt
for this advisory. Gaston is forecast to slowly weaken while the
cyclone completes its post-tropical transition in about 36 hours or
so. The official intensity forecast is similar to the previous one
and is in line with the IVCN intensity consensus model.

Gaston has begun its anticyclonic loop and is moving
east-southeastward, or 115/8 kt. The cyclone is expected to turn
toward the southeast today and southward along the southern
periphery of mid-tropospheric ridge building to the north through
Saturday morning while moving near the westernmost Azores.
Afterward, Gaston should generally move toward the west-southwest
and westward through the end of the period. The official forecast
is nudged slightly to the north of the previous one in the short
term, but closer after that, and is based on the various consensus
aids.


Key Messages:

1. Tropical storm conditions are occurring over portions of the
western Azores, and will likely spread to the central Azores later
today.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores today through Saturday. This rainfall may
result in landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 40.5N 29.6W 50 KT 60 MPH
12H 23/1800Z 39.7N 28.9W 50 KT 60 MPH
24H 24/0600Z 38.6N 29.4W 50 KT 60 MPH
36H 24/1800Z 38.2N 31.2W 50 KT 60 MPH...POST-TROPICAL
48H 25/0600Z 38.6N 33.7W 50 KT 60 MPH...POST-TROPICAL
60H 25/1800Z 38.6N 36.1W 45 KT 50 MPH...POST-TROPICAL
72H 26/0600Z 38.6N 38.0W 40 KT 45 MPH...POST-TROPICAL
96H 27/0600Z 39.1N 41.0W 35 KT 40 MPH...POST-TROPICAL
120H 28/0600Z 38.2N 45.3W 30 KT 35 MPH...POST-TROPICAL

$$
Forecaster Roberts
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Re: ATL: GASTON - Advisories

#12 Postby cycloneye » Fri Sep 23, 2022 10:07 am

BULLETIN
Tropical Storm Gaston Advisory Number 13
NWS National Hurricane Center Miami FL AL082022
300 PM GMT Fri Sep 23 2022

...GASTON STRENGTHENS WHILE MOVING TOWARDS THE CENTRAL AZORES...
...TROPICAL STORM CONDITIONS AND HEAVY RAINFALL EXPECTED OVER THE
WESTERN AND CENTRAL AZORES TODAY AND SATURDAY...


SUMMARY OF 300 PM GMT...1500 UTC...INFORMATION
----------------------------------------------
LOCATION...40.2N 29.1W
ABOUT 115 MI...180 KM N OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...ESE OR 120 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES




Tropical Storm Gaston Discussion Number 13
NWS National Hurricane Center Miami FL AL082022
300 PM GMT Fri Sep 23 2022

Gaston is improving in satellite presentation this morning.
Convection is re-forming and wrapping around the northern and
western sides of the circulation. A recent scatterometer pass
showed that Gaston was slightly stronger than the previous advisory
and the initial intensity has been increased to 55 kt. The
tropical-storm-force wind field was also expanded, especially in the
northwestern quadrant based on these data.

The cyclone has managed to retain its tropical characteristics for
now. Global model guidance suggests moderate to strong vertical
wind shear should gradually strip away convection from the core over
the next day or so. In spite of the relatively hostile conditions,
Gaston has managed to maintain its strength, therefore only gradual
weakening is forecast until the storm merges with a shortwave trough
in about 36 hours and becomes a post-tropical cyclone. The official
intensity forecast has been shifted slightly higher than the
previous advisory due to the initial intensity and is slightly
stronger than the consensus model aids.

The storm is moving east-southeastward at an estimated 120/6 kt. A
sharp turn to the south is expected shortly while Gaston traverses
the periphery of a mid-level ridge building to the north.
Afterward, the cyclone should generally move toward the
west-southwest and west, completing an anticyclone turn, through the
end of the period. The NHC forecast has been nudged slightly
northward once again from the previous forecast and lies between the
HCCA and TVCN multi-model consensus aids.

Key Messages:

1. Tropical storm conditions are occurring over portions of the
western Azores, and are spreading to the central Azores.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores today through Saturday. This rainfall may
result in landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 40.2N 29.1W 55 KT 65 MPH
12H 24/0000Z 39.4N 29.0W 55 KT 65 MPH
24H 24/1200Z 38.7N 30.2W 50 KT 60 MPH
36H 25/0000Z 38.7N 32.3W 50 KT 60 MPH...POST-TROPICAL
48H 25/1200Z 38.9N 34.8W 50 KT 60 MPH...POST-TROPICAL
60H 26/0000Z 39.0N 36.7W 45 KT 50 MPH...POST-TROPICAL
72H 26/1200Z 39.0N 38.6W 40 KT 45 MPH...POST-TROPICAL
96H 27/1200Z 38.9N 42.0W 35 KT 40 MPH...POST-TROPICAL
120H 28/1200Z 37.7N 46.2W 30 KT 35 MPH...POST-TROPICAL

$$
Forecaster Bucci
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Re: ATL: GASTON - Advisories

#13 Postby cycloneye » Fri Sep 23, 2022 3:46 pm

BULLETIN
Tropical Storm Gaston Advisory Number 14
NWS National Hurricane Center Miami FL AL082022
900 PM GMT Fri Sep 23 2022

...GASTON BRINGING HEAVY RAINFALL TO THE AZORES...
...TROPICAL STORM CONDITIONS EXPECTED OVER THE WESTERN AND CENTRAL
AZORES TONIGHT AND SATURDAY...


SUMMARY OF 900 PM GMT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...39.6N 28.7W
ABOUT 70 MI...110 KM N OF FAIAL ISLAND IN THE CENTRAL AZORES
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...S OR 180 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES



Tropical Storm Gaston Discussion Number 14
NWS National Hurricane Center Miami FL AL082022
900 PM GMT Fri Sep 23 2022

Convection has been sputtering in recent hours in the core of
Gaston. It appears the effects of strong vertical wind shear, dry
middle-level humidities and cool sea surface temperatures have
weakened the storm. Satellite Dvorak estimates from both TAFB and
SAB suggest the storm is now 45 kt while and earlier scatterometer
pass showed a decent area of 50-55 kt winds. The initial intensity
has been lowered to 50 kt to represent a blend of these estimates.

Gaston is moving southward at about 8 kt toward the central
Azores. A building mid-tropospheric ridge to the north is
expected to turn the storm towards the southwest early tomorrow.
The ridge will eventually steer Gaston westward in about a day
or so, and this motion is forecast to continue until the end of the
period. The official forecast track is very similar to the
previous advisory prediction except being slightly farther east in
the first 12 hours due to the present location and motion.

The tropical nature of Gaston seems to be winding down quickly.
Simulated satellite imagery from global models suggests the storm
will become fully post-tropical in about 36 hours. Statistical
model guidance insists that, despite strong to moderate vertical
wind shear and dry air, Gaston should only gradually weaken. The
NHC intensity forecast reflects this and is close the multi-model
consensus guidance and slightly lower than the previous forecast.
However, it is entirely possible Gaston could weaken more rapidly
than expected.

Key Messages:

1. Tropical storm conditions are expected over portions of the
western and central Azores.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores Friday into Saturday. This rainfall may
result in landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 39.6N 28.7W 50 KT 60 MPH
12H 24/0600Z 38.8N 29.1W 50 KT 60 MPH
24H 24/1800Z 38.5N 30.8W 50 KT 60 MPH
36H 25/0600Z 38.7N 33.2W 45 KT 50 MPH...POST-TROPICAL
48H 25/1800Z 38.9N 35.4W 45 KT 50 MPH...POST-TROPICAL
60H 26/0600Z 38.9N 37.3W 45 KT 50 MPH...POST-TROPICAL
72H 26/1800Z 38.9N 39.1W 40 KT 45 MPH...POST-TROPICAL
96H 27/1800Z 38.5N 43.1W 35 KT 40 MPH...POST-TROPICAL
120H 28/1800Z...DISSIPATED

$$
Forecaster Bucci
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Re: ATL: GASTON - Advisories

#14 Postby cycloneye » Fri Sep 23, 2022 9:52 pm

Tropical Storm Gaston Discussion Number 15
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Sat Sep 24 2022

Gaston continues to decline. Its associated deep convection has been
stripped away by strong northwesterly vertical wind shear, and the
cyclone now consists of a swirl of mainly low-level clouds with
embedded squalls. The initial intensity has been lowered to 45 kt
based on the latest Dvorak CI value from TAFB.

The storm has made its anticipated turn to the southwest and is now
moving at 220/7 kt. A building ridge to the north of Gaston should
turn the cyclone westward later today, and this motion is expected
to continue until the system dissipates late in the forecast
period. The latest NHC forecast track is little changed from the
previous one. On this track, Gaston will move near or over the
central and western Azores today.

Dry air, relatively cool SSTs of 24-25 degrees C, and persistent
strong vertical wind shear should cause Gaston to struggle to
maintain persistent organized deep convection. Therefore, further
weakening is anticipated, and the cyclone is forecast to become
post-tropical by tonight, if not sooner. The latest NHC intensity
forecast was lowered slightly from the previous one and is close to
the various multi-model consensus intensities.

Key Messages:

1. Tropical storm conditions are expected over portions of the
western and central Azores today.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores today. This rainfall may result in landslides and
areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 38.9N 29.5W 50 KT 60 MPH
12H 24/1200Z 38.4N 30.5W 45 KT 50 MPH
24H 25/0000Z 38.5N 32.4W 40 KT 45 MPH...POST-TROPICAL
36H 25/1200Z 38.7N 35.0W 35 KT 40 MPH...POST-TROPICAL
48H 26/0000Z 38.7N 36.8W 35 KT 40 MPH...POST-TROPICAL
60H 26/1200Z 38.6N 38.6W 35 KT 40 MPH...POST-TROPICAL
72H 27/0000Z 38.3N 40.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 28/0000Z 37.4N 44.9W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 29/0000Z...DISSIPATED

$$
Forecaster Latto
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Re: ATL: GASTON - Advisories

#15 Postby cycloneye » Sat Sep 24, 2022 3:53 am

Tropical Storm Gaston Discussion Number 16
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Sat Sep 24 2022

Since yesterday, Gaston has been transitioning to an asymmetric
warm core post-tropical cyclone. A Friday morning 1227Z METOP-C
scatterometer data confirmed that the transition had begun by
depicting growing asymmetry in the wind field with a hundred-mile
increase in gale-force winds in the northwest quadrant. Subsequent
surface winds less than 60 miles from the center were 20 kt or
less, all characteristics of a post-tropical/extratropical cyclone
wind profile. The initial intensity is set at a generous 45 kt and
is above the various subjective and objective satellite intensity
estimates.

As a result of increasing deep-layer shear and decreasing sea
surface temperature beneath the cyclone, Gaston's organized deep
convection has diminished considerably. Only a few convective
fragments remain well displaced to the southeast of the surface
center. Accordingly, further weakening is expected, and Gaston
should complete its post-tropical transition later today. A couple
of the global models, however, indicate a mid-latitude shortwave
trough/baroclinic zone interacting with post-tropical Gaston early
Sunday morning, which could create a flare-up of deep convection,
but this should be a short-lived event.

Gaston's initial motion is estimated to be west-southwestward, or
250/8 kt. Building high pressure over the northeast Atlantic
should continue to steer the post-tropical cyclone westward through
Monday morning, and west-southwestward until dissipation occurs
toward the end of the week. The official track forecast is a
little faster than the previous advisory and is nudged to the
south beyond 48 hours to agree more with the NOAA HFIP HCCA model.


Key Messages:

1. Tropical storm conditions over the western and central Azores
today should diminish this evening as Gaston moves away from the
islands.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores through Saturday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 38.6N 30.2W 45 KT 50 MPH
12H 24/1800Z 38.3N 31.5W 45 KT 50 MPH...POST-TROPICAL
24H 25/0600Z 38.7N 34.0W 40 KT 45 MPH...POST-TROPICAL
36H 25/1800Z 38.7N 36.4W 35 KT 40 MPH...POST-TROPICAL
48H 26/0600Z 38.1N 38.2W 35 KT 40 MPH...POST-TROPICAL
60H 26/1800Z 37.4N 39.9W 35 KT 40 MPH...POST-TROPICAL
72H 27/0600Z 36.6N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 28/0600Z 33.9N 47.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 29/0600Z...DISSIPATED

$$
Forecaster Roberts
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Re: ATL: GASTON - Advisories

#16 Postby cycloneye » Sat Sep 24, 2022 9:57 am

Tropical Storm Gaston Discussion Number 17
NWS National Hurricane Center Miami FL AL082022
300 PM GMT Sat Sep 24 2022

Gaston has lost most of its deep convection and it is currently an
exposed low-level circulation. The closest relatively deep
convective activity is south of Pico Island over 100 miles away
from the center and likely terrain-induced. Though a recent
scatterometer pass missed the center of Gaston, it did show an area
of tropical-storm-force winds of around 35 kt to the east of the
center. Therefore, the initial intensity has been lowered to 40
kt, slightly higher than the satellite intensity estimates.

Hostile environmental conditions have weakened Gaston considerably.
The strong vertical wind shear and dry mid-level humidities are not
expected to improve for the remainder of the forecast period, and
additional weakening is likely. The official forecast is similar to
the previous prediction and still shows Gaston becoming fully
post-tropical within 12 hours. A couple of the global models,
however, indicate a mid-latitude shortwave trough/baroclinic zone
interacting with post-tropical Gaston early Sunday morning could
develop isolated deep convection, but this should be a short-lived
event.

The storm is moving west-southwestward at an estimated 245/8 kt. A
building mid-level ridge to the north is expected to steer Gaston
to the west through Monday morning, and to the west-southwest
until it dissipates near the end of the week. The NHC forecast
track is shifted slightly south of the previous advisory track,
likely due to the southern shift of the initial position.


Key Messages:

1. Tropical storm conditions over the western and central Azores
today should diminish today as Gaston moves away from the islands.

2. Gaston is expected to produce heavy rainfall over the western
and central Azores through Saturday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 24/1500Z 38.0N 30.8W 40 KT 45 MPH
12H 25/0000Z 38.2N 32.5W 40 KT 45 MPH...POST-TROPICAL
24H 25/1200Z 38.4N 35.1W 35 KT 40 MPH...POST-TROPICAL
36H 26/0000Z 38.2N 37.0W 35 KT 40 MPH...POST-TROPICAL
48H 26/1200Z 37.5N 39.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 27/0000Z 36.7N 40.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 27/1200Z 35.6N 43.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 28/1200Z 33.0N 48.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 29/1200Z...DISSIPATED

$$
Forecaster Bucci
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Re: ATL: GASTON - Advisories

#17 Postby cycloneye » Sat Sep 24, 2022 3:50 pm

Tropical Storm Gaston Discussion Number 18
NWS National Hurricane Center Miami FL AL082022
900 PM GMT Sat Sep 24 2022

Gaston still lacks any deep convection near the center of its
circulation. There is a burst of convection, mentioned in the
previous advisory, that is now northwest of Faial island and over a
hundred miles from the center of the storm. The subjective and
objective Dvorak classifications have decreased to 30-40 kt.
Thus, the initial intensity has been lowered to 35 kt to be a blend
of these estimates.

Strong vertical wind shear and dry environmental conditions
continue to weaken Gaston. These adverse atmospheric conditions
are not expected to improve for the remainder of the forecast
period, and the storm should gradually weaken. The official
forecast is slightly lower than the previous prediction due to the
decrease in initial intensity. Gaston is still expected to become
fully post-tropical within 12 hours. Global model simulated
satellite imagery, however, indicate a mid-latitude shortwave
trough interacting with post-tropical Gaston early Sunday morning
could develop isolated deep convection, but this should be a
short-lived event.

Gaston has made its turn to the west and is moving 280/10 kt. The
storm should continue to move generally westward for the next day
or so as it is steered by a building ridge to the north. The ridge
is then expected to turn the cyclone to the west-southwest and
southwest through the end of the forecast period. The model
guidance has shifted to the north this forecast cycle. The
official track forecast follows the northward guidance trend and
now lies on the south side of the guidance, though north of the
previous advisory.


Key Messages:

1. Tropical storm conditions over the western Azores should
diminish overnight as Gaston moves away from the islands.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores through early Saturday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 38.2N 31.8W 35 KT 40 MPH
12H 25/0600Z 38.6N 33.7W 35 KT 40 MPH...POST-TROPICAL
24H 25/1800Z 38.6N 36.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 26/0600Z 38.3N 38.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 26/1800Z 38.0N 39.9W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 27/0600Z 37.5N 42.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 27/1800Z 37.0N 45.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 28/1800Z...DISSIPATED

$$
Forecaster Bucci
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Re: ATL: GASTON - Advisories

#18 Postby cycloneye » Sat Sep 24, 2022 9:34 pm

Tropical Storm Gaston Discussion Number 19
NWS National Hurricane Center Miami FL AL082022
300 AM GMT Sun Sep 25 2022

Gaston has been interacting with an upper-level trough just to its
west for the past several hours, which has helped to regenerate deep
convection over the northern semicircle. This has bought Gaston some
more time as a tropical cyclone. A pair of recent scatterometer
overpasses revealed a swath of 35-42 kt winds over the northern
semicircle of the tropical storm, which indicates that it is
stronger than previously estimated. Assuming some undersampling by
the scatterometer, the initial intensity has been adjusted to 45 kt
to reflect this new data.

The upper trough that is helping to maintain the deep convection is
forecast to lift northward later this morning and be replaced by a
ridge, which should induce strong northwesterly shear over Gaston.
The combination of this shear, relatively cool SSTs of about 24
degrees C, and the presence of dry air should cause Gaston's current
convection to dissipate today, resulting in the system becoming
post-tropical. The NHC intensity forecast was adjusted higher
through 24 h due to the adjusted initial intensity and is unchanged
from the previous forecast after that time.

Gaston continues its westward motion at 10 kt to the south of a
mid-level ridge. By Monday, the cyclone is forecast to turn
west-southwestward and possibly southwestward as the ridge builds
its northwest. The latest NHC track forecast is little changed from
the previous one and closely follows the track consensus guidance.


Key Messages:

1. Tropical storm conditions over the western Azores should diminish
by midday as Gaston moves away from the islands.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores through midday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 38.6N 33.4W 45 KT 50 MPH
12H 25/1200Z 38.9N 35.3W 45 KT 50 MPH...POST-TROPICAL
24H 26/0000Z 38.7N 37.6W 35 KT 40 MPH...POST-TROPICAL
36H 26/1200Z 38.4N 39.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 27/0000Z 37.9N 41.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 27/1200Z 37.2N 44.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 28/0000Z 36.8N 46.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 29/0000Z...DISSIPATED

$$
Forecaster Latto
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Re: ATL: GASTON - Advisories

#19 Postby cycloneye » Sun Sep 25, 2022 3:51 am

Tropical Storm Gaston Discussion Number 20
NWS National Hurricane Center Miami FL AL082022
900 AM GMT Sun Sep 25 2022

Gaston continues to generate an area of deep convection near and to
the north of the center, as the interaction with the upper-level
trough mentioned in the previous advisory continues to provide a
favorable environment. The initial intensity remains 45 kt based
on the earlier scatterometer data and a satellite intensity
estimate of 45 kt from TAFB.

The global models suggest that the favorable trough interaction
should end in the next 12 h or so, and after that time Gaston
should experience strong northwesterly shear in a convergent
upper-level environment. This, combined with cool sea surface
temperatures of 24-25C and a dry airmass should cause the
convection to dissipate and Gaston to become post-tropical. The
new intensity forecast has minor adjustments from the previous
forecast, with the most significant change being keep the system as
a tropical cyclone at the 12 h point.

Gaston has moved a little to the right of the previous forecast
with the initial motion 285/9. A building low- to mid-level ridge
to the north and northwest of the cyclone should cause it to turn
westward later today and then west-southwestward, with that motion
continuing until the system dissipates. Since the last advisory,
the track guidance has shifted southward in the 24-72 h period.
So, the new forecast track is also shifted southward, with the new
track just to the north of the consensus models.


Key Messages:

1. Tropical storm conditions over the western Azores should diminish
by midday as Gaston moves away from the islands.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores through midday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 39.0N 34.5W 45 KT 50 MPH
12H 25/1800Z 39.0N 36.5W 40 KT 45 MPH
24H 26/0600Z 38.7N 38.4W 35 KT 40 MPH...POST-TROPICAL
36H 26/1800Z 38.1N 40.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 27/0600Z 37.5N 42.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 27/1800Z 36.8N 45.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 28/0600Z 36.1N 48.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 29/0600Z...DISSIPATED

$$
Forecaster Beven
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Re: ATL: GASTON - Advisories

#20 Postby cycloneye » Sun Sep 25, 2022 3:36 pm

Tropical Storm Gaston Discussion Number 21
NWS National Hurricane Center Miami FL AL082022
300 PM GMT Sun Sep 25 2022

The large convective burst that fired overnight and this morning
appears to have lead to Gaston's center reforming under the deep
convection further to the north and west. This also evident in
GOES-16 GLM lightning data that showed a clear arcing pattern
embedded in the convection prior to the new center becoming evident
on visible satellite imagery. Since then, the convection has been
rapidly decaying, as the storm loses instability support from a
sharp upper-level trough as it moves into its axis. Subjective and
objective Dvorak numbers this morning were still CI 3.0/45-kt from
TAFB and UW-CIMSS ADT. While scatterometer data largely missed the
circulation earlier, it still showed tropical storm force winds
extending well to the northeast of the center. The initial intensity
is being maintained at 45 kt for this advisory.

Gaston, post reformation, has made its westward turn, with the
latest motion estimate at 270/10 kt. Gaston is currently situated
between an anomalously strong deep-layer ridge to its northeast, and
a more climatological ridge to its southwest. These features are
forecast to merge over the next 24-48 hours to the northwest of
Gaston, and should help steer the storm more to the west-southwest
for the remainder of its lifespan. The guidance this cycle is just a
bit further south and west compared to the previous cycle, and the
latest NHC track forecast was nudged in that direction, following
the consensus aids TVCN and HCCA.

Gaston might have had its last convective hurrah this morning, with
the GFS, ECMWF, CMC, and HWRF suggesting the storm will struggle to
produce organized convection from here on out. This could be related
to the upper-level flow pattern, where the storm is moving out of an
environment favorable for ascent into an environment favorable for
descent, limiting convection, especially as it continues to traverse
24-25C SSTs. The latest forecast still shows Gaston becoming a
post-tropical cyclone in about 24 hours, but if the convection does
not return before then, this evolution could occur sooner. The low
should persist another day or two before it opens up into a trough
in the subtropical Atlantic in about 72 hours, in agreement with the
majority of the global model guidance.

FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 39.4N 36.5W 45 KT 50 MPH
12H 26/0000Z 39.2N 38.0W 40 KT 45 MPH
24H 26/1200Z 38.7N 39.9W 35 KT 40 MPH...POST-TROPICAL
36H 27/0000Z 38.0N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 27/1200Z 37.4N 44.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 28/0000Z 36.8N 47.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 28/1200Z...DISSIPATED

$$
Forecaster Papin
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