atlantic Major Hurricane Gonzalo

[Thunder Snow]

Is it going to stay south of the jet do you think

[summer blizzard]

Is it going to stay south of the jet do you think

 

No. Forecast to become extra-tropical and satellite already shows it starting to merge with a frontal boundary.

[Thunder Snow]

So will it deepen as it heads towards the uk

[Ross Andrew Hemphill]

So will it deepen as it heads towards the uk

The current BBC pressure charts show it deepening a little and it will bring gales and severe gales to the UK. There will be more conversation about it over in the Atlantic Autumn Storms thread I'm sure.

[Lauren]

Webcam seems to have gone down.

[AderynCoch]

Best hurricane to watch for me since the 04/05 seasons. Plenty more between now and then but rarely strong hits on a place with accurate observations, webcams and no mountains to screw the wind field.

First time I've seen the eye pass over on a webcam. Ironic really that it happened in Bermuda, hundreds of miles from anywhere else.

 

The way it changed so quickly from roaring winds to eerie silence and back again was quite something.

[Lauren]

Is the webcam likely to do an edited version of it passing, like the other ones do of certain events? I ask because I fell asleep and missed the eye passing over and it is something I would like to see.

[summer blizzard]

Refusing to die. Sea surface temperatures of 10C but still maintaining a warm core for now.

[The PIT]

Refusing to die. Sea surface temperatures of 10C but still maintaining a warm core for now.

Perhaps then it will be more active than the present model runs show.

[Vorticity0123]

Refusing to die. Sea surface temperatures of 10C but still maintaining a warm core for now.

 

It is quite impressive to see for how long Gonzalo has been able to maintain a warm core, as it has reached a latitude above 50 N. This while the system is currently positioned over SSTS (sea surface tempeatures) of less than 15*C. The SSTS of the Atlantic can be seen below:

 

Sea surface temperature analysis of the Atlantic.

 

As of 18:45 UTC, Gonzalo is located near 50N, 45W, at the position of the white X. 

 

However, it looks like Gonzalo is close to become an extratropical system, if it has not already done so. This can be seen in the visible image loop of Gonzalo below:

 

Satellite image loop of Gonzalo. Click on the image for the loop itself.

 

What can be seen is that the cloud shield of Gonzalo is moving ahead of the low level circulation, usually indicative of extratropical transition. Furthermore, the convection associated with Gonzalo has become weak. Therefore, it is likely that NHC will declare Gonzalo an extratropical system soon.

 

EDIT: The NHC has just declared Gonzalo an extratropical system. Therefore, they have issued their final advisory on the system.

 

Sources:

http://www.nhc.noaa.gov/aboutsst.shtml

http://www.nhc.noaa.gov/

Edited October 19, 2014 by Vorticity0123

[matty40s]

 

maybe so, but it's the first time I can remember the NOAA wind warnings looking like this for the UK, only 24 hours out now.

[Vorticity0123]

 

 

maybe so, but it's the first time I can remember the NOAA wind warnings looking like this for the UK, only 24 hours out now.

 

The first thing that has to be emphasized is that transition of a tropical cyclone into an extratropical cyclone does not necessarily that the cyclone becomes a weak feature. In fact, a cyclone can strengthen after undergoing extratropical transition, when it is being fuelled by baroclinic energy.

 

In general, the structure of a tropical cyclone changes significantly when undergoing extratropical transition. What happens is that the cyclone transitions from a warm core into a cold-core system. In other words, the temperature at the upper levels (in height) of a cyclone transitions from warmer than its environment to colder than its environment. Furthermore, the cyclone becomes highly asymmetric and the convection/cloudiness associated with the system expands greatly in area, with the cloud structure taking a more frontal appearance.

 

A nice sequence of extratropical transition can be seen in the paper given below (extensive, yet technical explanation about extratropical transition):

http://moe.met.fsu.edu/~rhart/papers-hart/2003Jonesetal.pdf

 

Second, the fact that the chance of 35+ kt winds is so high over Scotland is mainly caused by the fact that the forecast time has been decreasing. In other words, given that the forecast is for fewer days out, it means that, as a rule, confidence in the forecast increases. 

 

However, as noted by Summer Blizzard, it is not very common to see systems still being tropical at such high latitude, especially in mid-October. It is not completely unprecedented, though, to see tropical cyclones at such high latitude. For example, hurricane Debby of 1982 became an extratropical storm at 51.5N¹.

 

This does not take away, though, that Scotland is likely to see some stormy conditions in about 24 hours out. 

 

I hope this clears things up a little bit  .

 

Sourcces:

http://moe.met.fsu.edu/~rhart/papers-hart/2003Jonesetal.pdf

http://www.theweatherprediction.com/basic/pressuretypes/

https://forum.netweather.tv/topic/34384-warm-and-cold-core-systems/

1: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%282001%29014%3C0546%3AACOTET%3E2.0.CO%3B2

Edited October 19, 2014 by Vorticity0123

[summer blizzard]

Yup. While Scotland may still get TS force sustained winds its highly unlikely that it will still have a defined warm core and as such it will be an extra-tropical storm.

 

Theoretically though if you could get enough of a thermal gradiant with the high sea temperatures in late August/early September then you could still have a tropical system.

 

I believe that Katia was similar to Gonzalo in being extra-tropical but Debby in (92?) was still a proper category 2.

[Somerset Squall]

Not sure what storm you are referring to there SB. Faith from 1966 is a classic example of a storm retaining tropical characteristics a LONG way north, over cool waters.

EDIT: should of read Vorticity's post more closely, I assume you are referring to Debby from 1982.

Edited October 19, 2014 by Somerset Squall

[summer blizzard]

http://en.wikipedia.org/wiki/Hurricane_Debbie_(1961)

 

Only 10 minute sustained winds though, i think it's 1 minute nowadays.

[Somerset Squall]

http://en.wikipedia.org/wiki/Hurricane_Debbie_(1961)

 

Only 10 minute sustained winds though, i think it's 1 minute nowadays.

 

Yes, it's 1 minute now. I've not looked at this one before, thanks SB

[Somerset Squall]

POST-TROPICAL CYCLONE GONZALO DISCUSSION NUMBER 30

NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014

500 PM AST SUN OCT 19 2014

The combined effect of sea-surface temperatures around 10C and

southwesterly vertical wind shear of more than 40 kt has finally

taken its toll on Gonzalo. The upper-level circulation is tilted

more than 100 nmi to the northeast of the low-level circulation

center, and an abundance of cold-air stratocumulus clouds has

wrapped all the way around the entire low-level circulation. Gonzalo

looks like a frontal low in satellite imagery, suggesting that the

system has completed its transformation into an extratropical

cyclone. The initial intensity has been decreased to 70 kt, which is

consistent with various decay models. Only gradual weakening is

expected during the next 48 hours.

The initial motion estimate is 060/45 kt. Gonzalo has turned toward

the east-northeast, and that general motion is expected for the next

24-36 hours, after which the cyclone is forecast to slow down

considerably and turn northward and be absorbed by a larger low

pressure system north of the British Isles by 72 hours. The NHC

track forecast is close to a blend of the GFS and ECMWF models, and

is near the latest forecast guidance provided by the NOAA Ocean

Prediction Center.

This is the last NHC advisory on Gonzalo. Additional information on

this system can be found in High Seas Forecasts issued by the

National Weather Service...under AWIPS header NFDHSFAT1 and WMO

header FZNT01 KWBC.

FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 51.6N 41.8W 70 KT 80 MPH...POST-TROP/EXTRATROP

12H 20/0600Z 53.6N 31.5W 65 KT 75 MPH...POST-TROP/EXTRATROP

24H 20/1800Z 56.5N 15.0W 50 KT 60 MPH...POST-TROP/EXTRATROP

36H 21/0600Z 58.5N 1.0W 50 KT 60 MPH...POST-TROP/EXTRATROP

48H 21/1800Z 64.5N 1.0W 50 KT 60 MPH...POST-TROP/EXTRATROP

72H 22/1800Z...ABSORBED

$$

Forecaster Stewart

[Steve C]

http://en.wikipedia.org/wiki/Hurricane_Debbie_(1961)

 

Only 10 minute sustained winds though, i think it's 1 minute nowadays.

 

I've wondered about that with regards to our weather too. I always thought that a 'gale day' definition was based on an average ten minute windspeed being >= 39 mph at some point during the day. Should it be 1 minute too?

 

Does it also mean that Americans would classify a 'marginal' hurricane as such, whereas the Japanese would only consider the same system as a strong tropical storm, due to the inevitable higher figure for 1 minute peak winds (IIRC the Japanese use 10 minutes still) 

Edited October 20, 2014 by Steve C