ATL: GASTON - Post-Tropical - Discussion

[JaxGator]

This season is really starting to get on my nerves and it's August 24th, what is happening?

Really? We have 8 storms already and Earl strengthening into a dangerous hurricane that hit Belize and Mexico. It is weird maybe that's August 24th though we still have time but remember, this season has been a bad one for a lot of folks so far.. Sorry, but imo, it's TOO soon for any season cancel posts or ones that imply it.

Not when yet another storm is underperforming in the MDR.

Besides Gaston looking nice (and it did), the main focus wasn't supposed to be in the MDR this season. Regardless of that, Gaston can still get pass the shear and become a great looking OTS hurricane. That's not a given but still.

[cycloneye]

18z GFS almost reach Bermuda but is also weaker.

[Kazmit]

Gaston's forecast cone seems to be finishing more and more west. Bermuda will need to keep an eye on this one. It could either be a repeat of Gonzalo (not very likely) or just a swell producer for them.

[CrazyC83]

Reading the discussion suggesting that the Global Hawk found 60 kt winds despite a degraded appearance make me strongly believe Gaston was a hurricane yesterday. If it doesn't restrengthen (and it should) it very likely will get a postseason bump.

[TropicalAnalystwx13]

I feel like I'm watching a replay of 2013, with everything struggling and severely under-performing the models. And this was supposed to be the ACE pump and in all likelihood it's already peaked (I'm not buying the re-intensification forecast--Humberto in 2013 was forecast the same with a wall of shear to the north and we saw how that turned out.)

It's been known for days that Gaston would develop quickly, level off or even weaken some due to temporarily increased shear, and then bomb out as it's recurving.

[Hammy]

I feel like I'm watching a replay of 2013, with everything struggling and severely under-performing the models. And this was supposed to be the ACE pump and in all likelihood it's already peaked (I'm not buying the re-intensification forecast--Humberto in 2013 was forecast the same with a wall of shear to the north and we saw how that turned out.)

It's been known for days that Gaston would develop quickly, level off or even weaken some due to temporarily increased shear, and then bomb out as it's recurving.

The models also had it significantly stronger than this, most at Cat 2, before weakening commenced--meanwhile it failed to even make hurricane intensity.

[Kazmit]

Models are trending more to the west (closer to Bermuda) before a recurve. I wonder why?

[TropicalAnalystwx13]

I feel like I'm watching a replay of 2013, with everything struggling and severely under-performing the models. And this was supposed to be the ACE pump and in all likelihood it's already peaked (I'm not buying the re-intensification forecast--Humberto in 2013 was forecast the same with a wall of shear to the north and we saw how that turned out.)

It's been known for days that Gaston would develop quickly, level off or even weaken some due to temporarily increased shear, and then bomb out as it's recurving.

The models also had it significantly stronger than this, most at Cat 2, before weakening commenced--meanwhile it failed to even make hurricane intensity.

The GFS had a Cat 2/3 by now, yes, but it should have been known it was too aggressive. The Euro consistently had a strong tropical storm around this time.

[pgoss11]

Models are trending more to the west (closer to Bermuda) before a recurve. I wonder why?

I wonder if the west trend of Gaston is what's causing a possible weakness in the ridge which may affect the track of 99L?

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 10
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST WED AUG 24 2016

Satellite intensity estimates from all agencies, recent ASCAT
measurements, and numerous dropsondes from the unmanned NASA
Global Hawk aircraft indicate that the initial intensity of Gaston
remains at 60 kt. Strong upper-level westerlies blowing around the
base of an upper low to the northwest of Gaston are already
affecting the symmetry of the cyclone, and the low-level center is
on the western edge of the convection. This strong westerly shear is
expected to last for about 36 hours, resulting in some weakening.
Most of the global models move the upper low toward the southwest,
and in about 2 days, Gaston will again be in a favorable environment
for intensification. On this basin, the NHC forecast weakens the
cyclone during the next 24 to 36 hours, and then calls for Gaston to
intensify and reach hurricane strength over the warm waters of the
central Atlantic. The forecast follows closely the SHIPS model and
the intensity consensus.

Gaston is moving toward the northwest or 310 degrees at 15 kt
steered by the flow between the subtropical high and the same
low that is causing the shear. As the low moves southwestward and
the ridge to the north of the cyclone amplifies, Gaston should turn
a little more toward the west-northwest with a decrease in forward
speed. The NHC forecast is the middle of the guidance envelope and
is basically on top of the latest multi-model consensus. No
significant changes were made to the previous track forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 18.6N 42.1W 60 KT 70 MPH
12H 25/1200Z 20.1N 44.0W 60 KT 70 MPH
24H 26/0000Z 22.3N 46.0W 50 KT 60 MPH
36H 26/1200Z 24.5N 48.3W 45 KT 50 MPH
48H 27/0000Z 26.3N 51.0W 55 KT 65 MPH
72H 28/0000Z 28.5N 55.5W 70 KT 80 MPH
96H 29/0000Z 30.5N 58.5W 80 KT 90 MPH
120H 30/0000Z 32.0N 59.5W 85 KT 100 MPH

$$
Forecaster Avila

[tolakram]

Funny, I posted a Blake tweet about the MJO rules not working. Appears they might in fact be having a significant impact on storm strength, fooling both reliable models.

[Ntxw]

It will cut down on some ACE if it waits till too far north to really deepen. I would be less comfortable with the ~25 units if it waits until after 25N to be a major.

[Yellow Evan]

I feel like I'm watching a replay of 2013, with everything struggling and severely under-performing the models. And this was supposed to be the ACE pump and in all likelihood it's already peaked (I'm not buying the re-intensification forecast--Humberto in 2013 was forecast the same with a wall of shear to the north and we saw how that turned out.)

It's been known for days that Gaston would develop quickly, level off or even weaken some due to temporarily increased shear, and then bomb out as it's recurving.

The models also had it significantly stronger than this, most at Cat 2, before weakening commenced--meanwhile it failed to even make hurricane intensity.

Not exactly.

First of all, Humberto was never forecast to get this strong, and regardless, managed to regenerate. Only way this doesn't re-intensify is if this starts having inner core problems (which isn't out of the question, but I see no reason why it would).



0z GFS initialization



24 hours ago



48 hours ago



72 hours ago



96 hours ago



ECMWF 24 hours ago



48 hours ago



72 hours ago



96 hours ago

In addition, the highest the SHIPS output ever had this at this point was 86 knots with most runs at low end hurricane intensity

[Florida1118]

000
WTNT62 KNHC 250415
TCUAT2

HURRICANE GASTON TROPICAL CYCLONE UPDATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1215 AM AST THU AUG 25 2016

...GASTON BECOMES THE THIRD HURRICANE OF THE ATLANTIC SEASON...

Dropsonde data from a NASA/NOAA Global Hawk mission indicate that
Gaston has strengthened to a hurricane. The maximum winds are
estimated to be 75 mph (120 km/h) with higher gusts.

SUMMARY OF 1215 AM AST...0415 UTC...INFORMATION
----------------------------------------------
LOCATION...18.7N 42.2W
ABOUT 1215 MI...1955 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...988 MB...29.47 INCHES

$$
Forecaster Berg

[galaxy401]

Look at that it did indeed make hurricane status. Probably been a hurricane for awhile now.

[Extratropical94]

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

[CrazyC83]

Look at that it did indeed make hurricane status. Probably been a hurricane for awhile now.

I'm guessing it peaked around 75 or 80 kt when it looked better late Tuesday or early Wednesday.

[Kazmit]

06z. Intensity models now going back up... with a lot showing a peak of a weak cat 2- weak cat 3.

[CrazyC83]

TXNT24 KNES 251210
TCSNTL

A. 07L (GASTON)

B. 25/1145Z

C. 20.0N

D. 43.7W

E. THREE/GOES-E

F. T3.5/3.5/W0.5/24HRS

G. IR/EIR/VIS/GMI/WINDSAT

H. REMARKS...THE SYSTEM IS CHARACTERIZED BY A LLCC LESS THAN 1/2 DEGREES
FROM THE COLD OVERCAST DUE TO SOUTHWESTERLY SHEAR RESULTING IN A DT OF
3.0. THE MET AND PT ARE 3.5. FT IS BASED ON MET.

I. ADDL POSITIONS

25/0546Z 18.8N 42.7W GMI
25/0852Z 19.4N 43.2W WINDSAT

Unchanged from the Global Hawk dropsonde time. I would probably either leave it at 65 kt or drop it slightly to 60 kt.

[CrazyC83]

AL, 07, 2016082512, , BEST, 0, 198N, 438W, 60, 992, TS,

Brought it down slightly. A bit surprised they haven't yet adjusted the BT from yesterday, since it probably had its (first?) peak around 0600Z August 24 (my guess is 75 kt knowing what the Global Hawk found later and the satellite degradation).