Huracan GASTON - Atlantico central

[Cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 AM AST THU AUG 25 2016

For much of yesterday afternoon and evening, the NASA/NOAA Global
Hawk unmanned aircraft flew a mission through Gaston. On the
aircraft's last pass through the storm, it released a dropsonde at
0243 UTC that measured a mean boundary layer wind of 80 kt and an
average wind of 77 kt in the lowest 150 m of the sounding near the
center of the cyclone. These numbers both support an intensity of
65 kt, and consequently Gaston was upgraded to a hurricane. The
sonde reported a minimum pressure of 995 mb with a 69-kt surface
wind, which equates to a central pressure of about 988 mb.

Despite Gaston becoming a hurricane, microwave data indicate that
the cyclone is tilted due to 20-25 kt of west-southwesterly shear.
The shear is expected to increase further during the next 12-24
hours when Gaston moves around the eastern side of an upper-level
low, and as a result, the hurricane is forecast to weaken back to a
tropical storm later today. The shear is then forecast to subside
in about 48 hours, and with sea surface temperatures expected to
increase, Gaston is likely to reintensify during the latter part of
the forecast period. The updated NHC forecast is higher than the
previous forecast during the first 48 hours primarily to account for
the higher initial intensity. After 48 hours, the official forecast
is unchanged and closely follows the SHIPS model and the ICON
intensity consensus.

Gaston continues to move northwestward, or 310 degrees at 15 kt,
along the southwestern edge of a mid-tropospheric high. A fairly
quick northwestward motion should continue for the next 36 hours,
with a turn toward the west-northwest expected by 48 hours when
Gaston moves around the north side of the aforementioned mid- to
upper-level low. Gaston is then expected to recurve toward the
north-northeast by day 5 as it moves through a break in the ridge
and toward the mid-latitude westerlies. The track models are in
agreement on this general scenario, although the ECMWF model is a
little bit slower and to the east of the other models, showing a
sharper turn by day 5. The new NHC track forecast is therefore a
little east of the previous forecast on days 4 and 5 and lies
closest to the HWRF and the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 19.5N 43.3W 65 KT 75 MPH
12H 25/1800Z 21.1N 44.8W 60 KT 70 MPH
24H 26/0600Z 23.4N 46.9W 55 KT 65 MPH
36H 26/1800Z 25.3N 49.4W 55 KT 65 MPH
48H 27/0600Z 26.7N 52.0W 60 KT 70 MPH
72H 28/0600Z 29.1N 56.0W 70 KT 80 MPH
96H 29/0600Z 31.0N 58.0W 80 KT 90 MPH
120H 30/0600Z 32.5N 57.5W 85 KT 100 MPH

$$
Forecaster Berg

[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



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]

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]

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]

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

[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

[Cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST FRI AUG 26 2016

The structure of Gaston appears to be slowly improving, with less
evidence of vertical shear than earlier today. Deep convection has
been forming fairly close to the center in a more symmetric fashion,
but still hasn't been able to persist for very long. Subjective
estimates are a little higher than earlier, but still support an
initial wind speed of 55 kt for this advisory.

Gaston should move into a low-shear, warm-water environment during
the next 2 or 3 days, which would usually support a great deal of
strengthening. However, a key hindering factor remains the nearby
low-level moisture, which is forecast to substantially decrease
during the next few days. This should temper the expected
intensification and reduce the chances for rapid strengthening.
Gaston is likely to encounter increasing upper-level flow beyond 3
days, which probably will start a weakening trend in combination
with gradually cooling SSTs. Model guidance is generally in good
agreement on this scenario, with less spread in the intensity
models than is typically seen. The new prediction is a blend of
the previous forecast and the intensity consensus.

Microwave data suggest that Gaston continues to move northwestward,
now at about 13 kt, a bit slower than before. The cyclone is
moving between a strong upper low to the southwest and a subtropical
ridge to its northeast. The ridge is forecast to gradually weaken,
resulting in Gaston decelerating over the next couple of days.
Steering currents get quite light in about 3 days, and the cyclone
is expected to turn northeastward or east-northeastward it moves
around the northwest side of a distant ridge over the eastern
Atlantic. Computer models are coming into better agreement on a
sharper, slower recurvature, first suggested by the ECMWF yesterday.
The latest NHC forecast is close to the previous one for the first
few days, then is trended eastward to follow the model trend.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0300Z 27.0N 50.8W 55 KT 65 MPH
12H 27/1200Z 28.0N 52.5W 60 KT 70 MPH
24H 28/0000Z 29.2N 54.1W 70 KT 80 MPH
36H 28/1200Z 30.2N 55.2W 80 KT 90 MPH
48H 29/0000Z 30.8N 55.7W 90 KT 105 MPH
72H 30/0000Z 31.8N 55.4W 95 KT 110 MPH
96H 31/0000Z 33.0N 52.0W 90 KT 105 MPH
120H 01/0000Z 35.0N 47.5W 80 KT 90 MPH

$$
Forecaster Blake

[Cycloneye]

...GASTON AGAIN A HURRICANE, NOW WITH 85-MPH WINDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...29.6N 54.2W
ABOUT 655 MI...1055 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...980 MB...28.94 INCHES


HURRICANE GASTON DISCUSSION NUMBER 22
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST SAT AUG 27 2016

Gaston has become a hurricane again with a well-defined eye on
microwave images that has been occasionally showing up on
conventional satellite pictures. Dvorak estimates are T4.5/77 kt
from both TAFB and SAB, so the initial wind speed is increased to 75
kt. The environment near Gaston, other than some dry mid-level air,
looks conducive for strengthening for the next day or so. While
the environment doesn't change much in the next couple of days
overall, Gaston is expected to move very slowly, which could upwell
some cooler water. Thus the wind speed forecast will be leveled
off after 24 hours. A more consistent weakening trend is expected
beyond 72 hours when the cyclone moves over colder waters and
experiences stronger shear. The latest NHC prediction is higher
than the previous one, mostly owing to the initial conditions, and
is close to a blend of the FSU Superensemble and the intensity
consensus.

Satellite fixes show that Gaston is moving slower to the northwest,
at about 7 kt. The storm should continue to decelerate over the
next day or so as it reaches a break in the subtropical ridge, and
have a slow motion to the north or northeast from 24 to 48 hours.
The next shortwave trough in the mid-latitude is forecast to reach
Gaston in about 3 days, which will likely cause the hurricane to
recurve to the east-northeast, albeit at a slower rate of speed than
you normally see over the North Atlantic. Guidance has not changed
much since the last cycle, and the official forecast is basically an
update of the previous one, a bit slower than the model consensus.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 29.6N 54.2W 75 KT 85 MPH
12H 28/1200Z 30.1N 54.7W 85 KT 100 MPH
24H 29/0000Z 30.7N 55.1W 95 KT 110 MPH
36H 29/1200Z 31.0N 55.2W 95 KT 110 MPH
48H 30/0000Z 31.4N 54.8W 90 KT 105 MPH
72H 31/0000Z 32.6N 52.2W 90 KT 105 MPH
96H 01/0000Z 34.6N 48.1W 85 KT 100 MPH
120H 02/0000Z 37.5N 42.0W 70 KT 80 MPH

$$
Forecaster Blake

[Cycloneye]

HURRICANE GASTON DISCUSSION NUMBER 24
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 AM AST SUN AUG 28 2016

The eye was fairly distinct a few hours ago, but recently it has
become slightly cloud-filled and the inner-core convection has
become less symmetrical. The current intensity is set at 90 kt,
in agreement with a Dvorak estimate from TAFB and objective ADT
values from UW-CIMSS. Assuming the slight degradation of the inner
core structure to be temporary, a little more strengthening is
expected within the next 12 to 24 hours. Gaston should remain in a
low to moderate vertical wind shear environment for the next
couple of days, which would allow the hurricane to more or less
maintain its intensity through 36-48 hours. By 72 hours and beyond,
increasing westerly shear should induce weakening. The official
intensity forecast is close to the multi-model consensus IVCN.

Steering currents are weak, and the initial motion is a
northwestward drift or 320/4 kt. Gaston's motion is being
partially blocked by a narrow subtropical ridge, and this scenario
should continue for the next day or so. The hurricane is expected
to gradually work its way through the ridge and, in 24 to 48 hours,
begin to move northeastward and east-northeastward as it enters the
mid-latitude westerlies. The official forecast is close to a
consensus of the ECMWF and GFS solutions.

FORECAST POSITIONS AND MAX WINDS

INIT 28/1500Z 30.5N 54.8W 90 KT 105 MPH
12H 29/0000Z 30.8N 55.3W 95 KT 110 MPH
24H 29/1200Z 31.2N 55.6W 95 KT 110 MPH
36H 30/0000Z 31.6N 55.1W 90 KT 105 MPH
48H 30/1200Z 32.4N 53.7W 90 KT 105 MPH
72H 31/1200Z 34.3N 49.4W 80 KT 90 MPH
96H 01/1200Z 36.5N 44.0W 75 KT 85 MPH
120H 02/1200Z 38.5N 36.5W 70 KT 80 MPH

$$
Forecaster Pasch