Graham Easterling wrote:

On Tuesday, December 9, 2014 7:21:02 PM UTC, Norman wrote:
Graham Easterling wrote:

On Tuesday, December 9, 2014 6:09:21 PM UTC, Togless wrote:
"Malcolm" wrote (quoting the Daily Express, I think):

"The deepest and most powerful low pressure system for A CENTURY
is currently hurtling towards the west coast where mammoth 50-ft
waves threaten mayhem."

Are they claiming that it's already the deepest and most powerful low
pressure system for a century (which should be easy enough to verify or
refute), or just that they expect it to be?

It certainly looks quite lively out there in the Atlantic...

Whilst 50' waves are very large, they occur in the north Atlantic every
winter. In fact 60' waves have been surfed in Ireland & Portugal.


It depends, of course, on whether we're talking about significant wave
height (which is the usual way to describe the sea state) or the maximum
wave height.

Down the more exposed parts of the west coast of the British Isles the once
in 50 year extreme significant wave height is around 16 metres (about 52
feet) so this would be a rare occurrence . West Cornwall is a little lower
with 14 metres (about 46 feet). However, with a significant wave height of
16 metres the highest occasional individual waves would be 27-30 metres
(around 90-100 feet).

So, if we are talking about 50 feet as a significant wave height around the
west coast of the British Isles this would be a rare and very notable
occurrence but if we are talking about a maximum wave height then it would
not be a notable occurrence.


--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org

I assumed from the wording, rightly or wrongly, that it was the maximum wave
height that was being referred to.

Dramatic Video of recent 60' reef break surfing in Portugal
https://www.youtube.com/watch?v=lFyp1o9CAvs (You can skip the Ad)

Move the decimal point to the left, and 6' is still big as far as I'm
concerned, these men are clearly mad!

Graham



The highest measured wave height I have seen so far is 15.9 metres (52 ft)
significant height at 0700z from the buoy at 59.1N 11.7W. It has decreased a
little since then and at 1300z it was 14.0m. The once in 50 year extreme
significant wave height for that location is of the order of 18-19 metres so,
for that location at least, it's a fair bit short of a once in 50 year event,
never mind a once in 100 year event.

At 53.2N 15.7W the highest reported so far is 14.1 metres significant height at
0600z. The once in 50 year event for that location is also around 18-19 metres.


--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org