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Old December 6th 18, 01:23 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance

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Old December 6th 18, 01:39 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

On Thursday, December 6, 2018 at 1:23:28 PM UTC, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


Just spotted, potential for the surf height to reach 35' at Gwenver, which is effectively the totally exposed end of Sennen.

Red Bull storm chasers conditions
https://www.youtube.com/watch?v=ExEYrg0r6zw

They really should stay between flags.

Graham
Penzance
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Old December 6th 18, 02:42 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

On 06/12/2018 13:23, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


NWW3 gives 15m sig wave height maximum under the low, mid-Atlantic on
Saturday, heading for the UK.
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Old December 6th 18, 03:28 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

On Thursday, December 6, 2018 at 2:41:24 PM UTC, N_Cook wrote:
On 06/12/2018 13:23, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


NWW3 gives 15m sig wave height maximum under the low, mid-Atlantic on
Saturday, heading for the UK.


The biggest average swell height, for any month, anywhere in the world, is in the N Atlantic, WSW of Ireland, in January.

That may surprise people, but the N Atlantic is a good shape for a long great circle route. The stormiest weather might be in thee southern hemisphere, but Antarctica rather gets in the way of swells on a great circle route.

Graham
Penzance
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Old December 6th 18, 04:41 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

Graham Easterling wrote:

On Thursday, December 6, 2018 at 2:41:24 PM UTC, N_Cook wrote:
On 06/12/2018 13:23, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to
arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge,
11m has a return period of 5 years. However, it is set to be not
only the biggest swell so far, but also has a long period -
making it powerful and able to refract into normally sheltered
spots, and will be associated with a fairly big tide & strong to
gale onshore winds. The 1st really destructive swell to hit the
north coast since last winter. The sand levels on most north
coast beaches are generally quite high at the moment, certainly
for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


NWW3 gives 15m sig wave height maximum under the low, mid-Atlantic
on Saturday, heading for the UK.


The biggest average swell height, for any month, anywhere in the
world, is in the N Atlantic, WSW of Ireland, in January.

That may surprise people, but the N Atlantic is a good shape for a
long great circle route. The stormiest weather might be in thee
southern hemisphere, but Antarctica rather gets in the way of swells
on a great circle route.

Graham
Penzance


I recall enormously high and long swells at Ocean Station "Juliette"
(52.5N 20.0W). In the deep ocean water a swell with a period of 18
seconds has a crest to crest wavelength of just over 500m. Very
impressive when viewed from a ship just under 80m in length :-)

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
twitter: @TideswellWeathr


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Old December 8th 18, 10:01 AM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

On Thursday, December 6, 2018 at 1:23:28 PM UTC, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


Up to 6m at Sevenstones yesterday, dropped back a bit now, for a while. 11m reached at M6 to the west of Ireland.

It was very rough yesterday, with the big swell and an onshore wind gusting 60mph at places like Lands End & The Island, St Ives, already quite a bit of sand removed from the top of Sennen beach.

For anyone interested, this is the MetO page linking to marine observations
https://www.metoffice.gov.uk/public/...e/observations

For some reason Sevenstones is listed under south coast. I would have though west coast or offshore, but there you are.

Lull in the swell currently, but still thoroughly unpleasant conditions
Currently low tide - you certainly wouldn't think so
https://magicseaweed.com/Live-Sennen-Webcam/65/
Surges going well up the beach with the big sets.

Graham
Penzance
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Old December 8th 18, 10:46 AM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

On 08/12/2018 10:01, Graham Easterling wrote:
On Thursday, December 6, 2018 at 1:23:28 PM UTC, Graham Easterling wrote:
The biggest swell of the Autumn/Winter is now almost certain to arrive on Sunday.

Forecast to peak at around 8m at Sevenstones. This is not huge, 11m has a return period of 5 years. However, it is set to be not only the biggest swell so far, but also has a long period - making it powerful and able to refract into normally sheltered spots, and will be associated with a fairly big tide & strong to gale onshore winds. The 1st really destructive swell to hit the north coast since last winter. The sand levels on most north coast beaches are generally quite high at the moment, certainly for winter. I expect to see some significant drops.

Surf forecast well 25' for Sennen, with an onshore gale
https://magicseaweed.com/Sennen-Surf-Report/4/

Graham
Penzance


Up to 6m at Sevenstones yesterday, dropped back a bit now, for a while. 11m reached at M6 to the west of Ireland.

It was very rough yesterday, with the big swell and an onshore wind gusting 60mph at places like Lands End & The Island, St Ives, already quite a bit of sand removed from the top of Sennen beach.

For anyone interested, this is the MetO page linking to marine observations
https://www.metoffice.gov.uk/public/...e/observations

For some reason Sevenstones is listed under south coast. I would have though west coast or offshore, but there you are.

Lull in the swell currently, but still thoroughly unpleasant conditions
Currently low tide - you certainly wouldn't think so
https://magicseaweed.com/Live-Sennen-Webcam/65/
Surges going well up the beach with the big sets.

Graham
Penzance


For the time of my awareness and monitoring NOAA NWW3 wave model outputs
I don't remember seeing it push anything more than 4m sig wave heights
into the Eng channel beyond the Brest-Newlyn line.
But for midnight tonight gives 5.5m to the Cherbourg Peninsular and 6m
for 06:00 tomorrow.

I was not aware of that MetO site

https://www.metoffice.gov.uk/public/...e/observations

too much bloatware (Waiting for .... ) or something for my 2 browsers
but I could pick up individual pages to go to, eg

https://www.metoffice.gov.uk/public/...vations/162103

seemingly MetO dumming down CLV to channel lightship

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Old December 8th 18, 12:28 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter



For the time of my awareness and monitoring NOAA NWW3 wave model outputs
I don't remember seeing it push anything more than 4m sig wave heights
into the Eng channel beyond the Brest-Newlyn line.


You've missed quite a bit then!

I would say 6m occurs every winter at some time off the Lizard (which is east of Newlyn)

11m has a return period of 5 years just off Lands End at Sevenstones, so I should think the 5 year return period in open sea to the south of Mount's Bay (off Newlyn) is around 10m. Norman is the expert on return periods.

I've been across Mounts Bay in a RIB, when the swell was certainly over 4m, on a fine summers day. Surfers were being towed out from Porthcurno on jet skis to catch a rare summer big wave.

I should add that the 7-8m forecasts for Seventones tomorrow is a typical winter storm height, it just happens to coincide with a directly onshore gale (for the N coast) & biggish tides. A combination of factors could make it damaging. It got me interested as there's been nothing of note on the N coast this Autumn winter, it's the south coast that's been more affected so far.

It was twice that height in March 2014.
A Picture from then. The lightouse is 35m, the helipad is higher. Local opinion is the the biggest sets at Longships were 20m on that day.
http://www.sennen-cove.com/ts1.htm
and
http://www.sennen-cove.com/10mar31.htm

2016 (my photos) about 11m off Lands End (38' peak sig wave height at Sevenstones)
http://www.turnstone-cottage.co.uk/StormImogen2016.pdf

Graham
Penzance
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Old December 8th 18, 04:15 PM posted to uk.sci.weather
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Default Cornish N coast - 1st damaging swell of the Autumn Winter

Graham Easterling wrote:



For the time of my awareness and monitoring NOAA NWW3 wave model
outputs I don't remember seeing it push anything more than 4m sig
wave heights into the Eng channel beyond the Brest-Newlyn line.


You've missed quite a bit then!

I would say 6m occurs every winter at some time off the Lizard (which
is east of Newlyn)

11m has a return period of 5 years just off Lands End at Sevenstones,
so I should think the 5 year return period in open sea to the south
of Mount's Bay (off Newlyn) is around 10m. Norman is the expert on
return periods.


The once in 50-years Hsig in the open sea south of Mount's Bay is
13-14m so I reckon you estimate of 10m for the 5-year return probably
isn't too far from the mark. Even up at Channel Light Vessel the
50-year return Hsig is of the order of 10-11m so I would think they'll
get up to 6m in most winters.


--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
twitter: @TideswellWeathr


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