ATL: GASTON - Post-Tropical - Discussion

[cycloneye]

TROPICAL STORM LESTER DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016
900 AM MDT THU AUG 25 2016

The cloud pattern of Lester continues to gradually become better
organized, with developing convective banding features surrounding
a small CDO and expanding upper-level outflow. Dvorak intensity
estimates from both TAFB and SAB are 45 kt, and that value is used
for the advisory intensity. The global models forecast a low-shear
environment for Lester over the next several days, and the cyclone
should remain over SSTs warmer than 27 deg C throughout most of the
forecast period. Steady strengthening is forecast until late in
period when Lester approaches marginal SSTs. The official forecast
is close to the intensity model consensus, IVCN.

Geostationary and microwave satellite fixes yield a motion estimate
of about 295/10 kt. The track forecast reasoning remains about the
same as in the previous advisory. Throughout the forecast period,
the tropical cyclone should remain embedded in the flow on the south
side of a broad mid-tropospheric ridge over the eastern North
Pacific. A gradual turn toward the west, at a slightly faster pace
than shown in the previous official forecast, is anticipated. The
NHC track prediction is very close to the latest multi-model
consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 16.6N 112.5W 45 KT 50 MPH
12H 26/0000Z 17.0N 113.6W 55 KT 65 MPH
24H 26/1200Z 17.5N 115.0W 65 KT 75 MPH
36H 27/0000Z 17.7N 116.4W 70 KT 80 MPH
48H 27/1200Z 17.8N 118.0W 75 KT 85 MPH
72H 28/1200Z 17.9N 122.3W 80 KT 90 MPH
96H 29/1200Z 18.0N 127.5W 80 KT 90 MPH
120H 30/1200Z 18.0N 132.5W 75 KT 85 MPH

$$
Forecaster Pasch

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST THU AUG 25 2016

The satellite presentation of Gaston has degraded some since the
previous advisory, with deep convection bursting northeast of the
center due to about 25 kt of southwesterly shear as analyzed by
UW-CIMSS. An ASCAT-B pass from 1212 UTC was helpful in locating the
center and showed peak winds of around 55 kt, which support an
intensity of 60 kt for this advisory, a little above the latest
Dvorak estimates of T3.5/55 kt. The strong shear is forecast to
continue for the next 24 hours until Gaston moves poleward of an
upper-level low currently located to its west. Given the shear and
SSTs around 27-28C, little change in intensity, or perhaps some
slight weakening, is expected in the first 24 hours. After that
time, the shear decreases and Gaston moves over SSTs of 29-30C,
which should allow for strengthening through the rest of the
forecast period. The NHC intensity forecast is a little higher than
the previous one later in the period and is close to the SHIPS model
and the IVCN intensity consensus.

The initial motion estimate is 315/15. Gaston should continue
moving quickly northwestward for the next 24 to 36 hours around a
mid-level ridge centered to its northeast. Ridging then builds
westward to the north of the tropical cyclone, leading to a decrease
in forward speed and a turn toward the west-northwest in 48 hours.
Late in the period, Gaston will turn poleward into a weakness along
60W and then begin to recurve into the mid-latitude westerlies. The
track model guidance agrees on this general scenario, however, there
are some differences in the timing and sharpness of recurvature.
The GFS, GFS ensemble mean, and UKMET are on the left side of the
guidance envelope with a broader turn, while the ECMWF, HWRF, and
GFDL show a sharper turn on the right side of the guidance. Given
the uncertainty, the NHC forecast remains near the previous one in
the middle of the guidance envelope, and is close to the TVCN
multi-model consensus.

The initial and forecast 34-kt and 50-kt wind radii were adjusted
based on data from the ASCAT pass.

FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 20.4N 44.4W 60 KT 70 MPH
12H 26/0000Z 22.1N 45.9W 55 KT 65 MPH
24H 26/1200Z 24.4N 48.2W 55 KT 65 MPH
36H 27/0000Z 26.0N 50.9W 60 KT 70 MPH
48H 27/1200Z 27.1N 53.1W 65 KT 75 MPH
72H 28/1200Z 29.4N 56.6W 80 KT 90 MPH
96H 29/1200Z 31.0N 58.0W 90 KT 105 MPH
120H 30/1200Z 33.0N 57.0W 90 KT 105 MPH

$$
Forecaster Brennan

[cycloneye]

...GASTON WEAKENS TO A TROPICAL STORM OVER THE CENTRAL ATLANTIC...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...20.4N 44.4W
ABOUT 1160 MI...1865 KM ENE OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...992 MB...29.30 INCHES

[cycloneye]

Phil turns humorous.

 https://twitter.com/philklotzbach/status/768857789796012032

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST THU AUG 25 2016

Strong southwesterly shear continues to take a toll on Gaston. The
cloud pattern has become more assymetric with all of the deep
core convection located north and east of the center. This was
confirmed by a recent SSMIS microwave overpass that showed
significant southwest to northeast tilt between the low- and
mid-level centers. Objective Dvorak T-numbers have decreased and
subjective intensity estimates from TAFB and SAB support an initial
wind speed of 55 kt. A large upper-level low near 23N 54W that is
moving southwestward is expected to continue to produce an
unfavorable upper-level environment over Gaston for another 12 to
18 hours. Some additional weakening is possible tonight, but the
official NHC forecast shows little change in strength through
Friday. After that time, Gaston should be moving around the
northern portion of the upper-low and into a more favarable
upper-level wind pattern. This combined with warm SSTs and a moist
atmosphere should allow Gaston to re-strengthen over the weekend
and once again become a hurricane. The updated NHC intensity
forecast is slightly above the previous advisory after 36 hours, and
is in good agreement with the latest SHIPS guidance.

The initial motion remains northwestward at 15 kt. Gaston should
move northwestward during the next day or so around a mid-level
ridge over the east-central Atlantic. In 36 to 48 hours, a ridge is
forecast to build to the north of Gaston, which should cause the
cyclone to turn west-northwestward. Early next week, the ridge
is forecast to weaken and Gaston is expected to turn northward,
then recurve into the mid-latitude westerlies in 4 to 5 days. The
track guidance is in good agreement during the first 48 hours, but
there is some spread as to what longitude recurvature begins. The
ECMWF shows a slower motion near the end of the forecast period and
a track along the eastern side of the guidance envelope, while the
GFS and GFS ensemble mean are along the western edge. The NHC track
foreast remains near the middle of the guidance envelope and is in
closest agreement with UKMET, FSSE, and multi-model consensus.


FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 21.6N 45.5W 55 KT 65 MPH
12H 26/0600Z 23.4N 47.1W 55 KT 65 MPH
24H 26/1800Z 25.5N 49.6W 55 KT 65 MPH
36H 27/0600Z 27.0N 52.3W 60 KT 70 MPH
48H 27/1800Z 28.1N 54.7W 70 KT 80 MPH
72H 28/1800Z 30.2N 57.0W 85 KT 100 MPH
96H 29/1800Z 31.8N 57.7W 95 KT 110 MPH
120H 30/1800Z 34.0N 55.0W 95 KT 110 MPH

$$
Forecaster Brown

[cycloneye]

...GASTON WEAKENS A LITTLE MORE BUT FORECAST TO RE-STRENGTHEN
BY SATURDAY...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...21.6N 45.5W
ABOUT 1105 MI...1780 KM ENE OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...994 MB...29.36 INCHES

[Kazmit]

NHC predicts a re-strengthen to a strong Cat 2. Looks like a major is not out of the question.

FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 21.6N 45.5W 55 KT 65 MPH
12H 26/0600Z 23.4N 47.1W 55 KT 65 MPH
24H 26/1800Z 25.5N 49.6W 55 KT 65 MPH
36H 27/0600Z 27.0N 52.3W 60 KT 70 MPH
48H 27/1800Z 28.1N 54.7W 70 KT 80 MPH
72H 28/1800Z 30.2N 57.0W 85 KT 100 MPH
96H 29/1800Z 31.8N 57.7W 95 KT 110 MPH
120H 30/1800Z 34.0N 55.0W 95 KT 110 MPH

[cycloneye]

 https://twitter.com/TropicalTidbits/status/768960102883856385

[Yellow Evan]

----- Current Analysis -----
Date : 25 AUG 2016 Time : 231500 UTC
Lat : 22:03:17 N Lon : 45:52:56 W


CI# /Pressure/ Vmax
4.4 / 982.0mb/ 74.6kt


Final T# Adj T# Raw T#
4.4 4.4 2.2

Center Temp : -38.1C Cloud Region Temp : -43.6C

Scene Type : UNIFORM CDO CLOUD REGION w/ MW EYE

[Steve820]

I was actually a little surprised earlier to see it reach hurricane intensity despite all the wind shear. After the shear dies down, I won't be surprised to see it re-intensify to Category 2 strength, or even major hurricane status.

[Kazmit]

I was actually a little surprised earlier to see it reach hurricane intensity despite all the wind shear. After the shear dies down, I won't be surprised to see it re-intensify to Category 2 strength, or even major hurricane status.

The 18z intensity models show a re-intensification to at least Cat 2 strength, with a few indicating a weak Cat 3 major hurricane. I think this could bomb out while making it's closest approach to Bermuda, on Sunday/Monday. By the way, you're on Hurricanes Wiki right? I love lurking around on those forums.

[Steve820]

I was actually a little surprised earlier to see it reach hurricane intensity despite all the wind shear. After the shear dies down, I won't be surprised to see it re-intensify to Category 2 strength, or even major hurricane status.

The 18z intensity models show a re-intensification to at least Cat 2 strength, with a few indicating a weak Cat 3 major hurricane. I think this could bomb out while making it's closest approach to Bermuda, on Sunday/Monday. By the way, you're on Hurricanes Wiki right? I love lurking around on those forums.

I hope it bombs out as long as it's a fishspinner (since Bermuda could otherwise see impacts). Yes, I'm on Hurricanes Wiki

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST THU AUG 25 2016

Gaston continues to have an asymmetric satellite appearance due to
strong southwesterly shear. Still, the cyclone is producing
persistent deep convection near the center, and Dvorak estimates
suggest the initial wind speed remains near 55 kt. The shear
should decrease tomorrow due to Gaston moving into a favorable
position to the north of an upper-level low. In addition, the
water temperatures are forecast to be warming up during the next
few days, which should also promote strengthening. Due to recent
microwave data showing that the inner core has been disrupted, only
a slow intensification is shown in this forecast. In the longer
term, models are not in great agreement on the upper-level wind
pattern, and I have elected to level off the intensification. The
new NHC prediction is a blend of the previous one and the model
consensus. It should be noted that, while not explicitly shown
below, a majority of the guidance show Gaston becoming a major
hurricane at some time in the day 3 to 5 period.

The initial motion remains northwestward at 15 kt. Gaston should
move northwestward during the next day or so around a mid-level
ridge over the east-central Atlantic. In about 36 hours, the
ridge is forecast to build to the north of Gaston, which will likely
cause the cyclone to turn west-northwestward. Early next week,
Gaston should turn northward as the ridge weakens, then recurve into
the mid-latitude westerlies in 4 days or so. Model guidance,
however, is not in good agreement on the exact details, with timing
and speed differences in both the tropical cyclone's position and
the potential mid-latitude shortwave that causes recurvature. Since
there have been no substantive changes to the model guidance in this
cycle, the new NHC prediction is basically just an update of the
previous one. It is fair to say that the end of this forecast is
of pretty low confidence.



FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 22.8N 46.4W 55 KT 65 MPH
12H 26/1200Z 24.5N 48.1W 55 KT 65 MPH
24H 27/0000Z 26.2N 50.7W 60 KT 70 MPH
36H 27/1200Z 27.5N 53.1W 65 KT 75 MPH
48H 28/0000Z 28.6N 54.9W 75 KT 85 MPH
72H 29/0000Z 30.5N 57.0W 90 KT 105 MPH
96H 30/0000Z 32.5N 57.0W 95 KT 110 MPH
120H 31/0000Z 34.5N 53.0W 95 KT 110 MPH

$$
Forecaster Blake

[cycloneye]

...GASTON EXPECTED TO BECOME A HURRICANE AGAIN OVER THE WEEKEND...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...22.8N 46.4W
ABOUT 1075 MI...1725 KM ENE OF THE LEEWARD ISLANDS
ABOUT 1300 MI...2095 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...997 MB...29.44 INCHES

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 AM AST FRI AUG 26 2016

Gaston is right in the thick of 20-25 kt of southwesterly shear,
and the low-level center appears to be near or just inside the
southern edge of a ragged central dense overcast. Because Dvorak
Current Intensity estimates from TAFB and SAB remain 3.5, the
initial intensity is held at 55 kt. With Gaston now moving around
the northeastern side of a mid- to upper-level low, the vertical
shear is expected to quickly decrease to below 10 kt within the next
12-24 hours. In addition, sea surface temperatures are forecast to
increase by another degree or two. Therefore, Gaston is likely to
begin strengthening later today, and it should reintensify to a
hurricane by tonight or on Saturday. Strengthening is anticipated
to continue through days 3 and 4, with Gaston nearing or possibly
reaching major hurricane intensity, followed by some weakening on
day 5 due to an increase in westerly shear. The reliable intensity
models are all within 10-15 kt of each other for the entire
forecast period, and the NHC forecast is therefore very close to
the ICON intensity consensus.

Gaston continues to move northwestward, or 320 degrees at 15 kt.
The cyclone is expected to maintain a generally northwestward track
but slow down considerably during the next few days after it moves
north of the aforementioned mid- to upper-level low and enters a
break in the subtropical ridge. After 72 hours, Gaston is expected
to reach the mid-latitude westerlies, and a sharp recurvature with
acceleration is forecast at the end of the forecast period. While
all the track models agree on this scenario, there continue to be
differences in the sharpness of Gaston's turn and its forward speed,
especially after the turn. Still, the updated NHC track forecast
is not too different from the previous one, and it is closest to a
clustering of models that includes the GFS, the Florida State
Superensemble, and the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 23.9N 47.6W 55 KT 65 MPH
12H 26/1800Z 25.5N 49.5W 60 KT 70 MPH
24H 27/0600Z 27.0N 52.1W 65 KT 75 MPH
36H 27/1800Z 28.2N 54.2W 70 KT 80 MPH
48H 28/0600Z 29.2N 55.7W 85 KT 100 MPH
72H 29/0600Z 30.8N 57.1W 95 KT 110 MPH
96H 30/0600Z 32.2N 55.8W 95 KT 110 MPH
120H 31/0600Z 34.0N 51.5W 90 KT 105 MPH

$$
Forecaster Berg

[tolakram]

live visible

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=26&lon=-47&info=vis&zoom=1&width=1024&height=768&type=Animation&quality=92&palette=ir1.pal&numframes=5&mapcolor=gray

[CrazyC83]

Given that a new ASCAT pass showed 55 kt winds, I wonder if it might have strengthened a tad in the past few hours?

[Hammy]

Center exposed once again, I doubt they'll increase the intensity on the next advisory.

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 16
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST FRI AUG 26 2016

Gaston continues to be adversely impacted by about 20 kt of
southwesterly vertical shear because of a strong upper low to the
southwest. The shear is forcing the diminished deep convection to
be primarily located north of the center. The TAFB and SAB
current intensities indicated 55 kt at 12Z, which is supported by a
1330Z ASCAT-B scatterometer pass which just became available.

As Gaston moves away from the upper-level low, the shear should drop
fairly dramatically to between 5 and 10 kt by tomorrow. The shear
should stay low through about 72 h while the cyclone traverses over
quite warm waters. After about three days, Gaston should encounter
strong mid-latitude upper-level westerlies and a return of hostile
shear at the same time that SSTs steadily drop. The official NHC
forecast is for steady intensification between days one and three,
with gradual weakening thereafter. This forecast is based upon the
IVCN intensity model consensus and is very similar to that from the
previous advisory.

Gaston's initial position is very well known, due to the center
being along the edge of the deep convection. The tropical storm is
moving toward the north-northwest at a rapid 15-kt clip, as it's
being steered between the strong upper low and a subtropical ridge
to its northeast. Around 72 h, Gaston should slow to a crawl as it
reaches a weak steering pattern. But by the end of the forecast
period, the system should be accelerating northeastward as it enters
the mid-latitude westerlies. The track forecast is based upon the
tightly clustered members of the TVCN track model consensus and is
just slightly north of the previous advisory due to Gaston's initial
position being more north than previously anticipated.

The initial 34- and 50-kt wind radii were made slightly larger
based upon an AMSU satellite pass and the wind radii forecast is
similar to the RVCN consensus technique.

FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 25.2N 48.3W 55 KT 65 MPH
12H 27/0000Z 26.7N 50.1W 55 KT 65 MPH
24H 27/1200Z 27.9N 52.5W 65 KT 75 MPH
36H 28/0000Z 29.0N 54.3W 75 KT 85 MPH
48H 28/1200Z 29.9N 55.5W 85 KT 100 MPH
72H 29/1200Z 31.2N 56.1W 95 KT 110 MPH
96H 30/1200Z 32.5N 54.0W 90 KT 105 MPH
120H 31/1200Z 34.5N 50.0W 80 KT 90 MPH

$$
Forecaster Landsea

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 17
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST FRI AUG 26 2016

The hostile vertical shear from an upper low to Gaston's southwest
appears to be dropping with the SHIPS and CIMSS shear analyses down
to about 15 kt. The deep convection, however, is still mainly north
of the center and lacks significant banding features. SAB and TAFB
Dvorak current intensity estimates range from 45 to 55 kt, down
slightly from earlier today. In deference to the 1330Z ASCAT
scatterometer pass and the very robust low-level circulation evident
in the visible imagery during the day, the maximum winds are kept at
55 kt.

As Gaston moves away from the upper-level low, the shear should
continue to drop to values between 5 and 10 kt by tomorrow. The
shear should then stay low through about 72 h while the cyclone
traverses over quite warm waters. A key uncertainty in the
intensity forecast is from the environmental low-level moisture,
which may decrease substantially during the next few days. This
could reduce the otherwise quite conducive conditions that Gaston
should soon experience. After about three days, Gaston is likely to
encounter strong mid-latitude upper-level westerlies and a return of
hostile shear while SSTs steadily drop. The official NHC forecast is
for steady intensification between days one and three, with gradual
weakening thereafter. This forecast is based upon a blend of the
tightly packed HWRF/COAMPS/SHIPS/LGEM models and is the same as in
the previous advisory.

Gaston's center is just tucked in on the southern edge of the deep
convection, allowing for a confident assessment of the initial
position. The tropical storm is moving toward the northwest at a
15-kt clip, as it is being steered between the strong upper low and
a subtropical ridge to its northeast. Around 72 h, Gaston should
slow to a crawl as it reaches a weak steering pattern. But by the
end of the forecast period, the system should be accelerating
northeastward as it enters the mid-latitude westerlies. The track
forecast is based upon a blend of the GFS and ECMWF global models
and is nearly the same from that in the previous advisory.

The initial 34- and 50-kt wind radii were only slightly tweaked
based upon the ASCAT scatterometer pass and the wind radii forecast
is similar to the RVCN consensus technique.


FORECAST POSITIONS AND MAX WINDS

INIT 26/2100Z 26.2N 49.7W 55 KT 65 MPH
12H 27/0600Z 27.4N 51.5W 55 KT 65 MPH
24H 27/1800Z 28.6N 53.5W 65 KT 75 MPH
36H 28/0600Z 29.7N 54.8W 75 KT 85 MPH
48H 28/1800Z 30.4N 55.8W 85 KT 100 MPH
72H 29/1800Z 31.5N 56.0W 95 KT 110 MPH
96H 30/1800Z 32.5N 53.5W 90 KT 105 MPH
120H 31/1800Z 34.5N 49.0W 80 KT 90 MPH

$$
Forecaster Landsea