Malcolm wrote:
In article , Norman
writes
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.
I notice that the forecast of the sea state for my local inshore water, Mull
of Kintyre to Ardnamuchan Point, is:
"Very rough or high, becoming very high, occasionally phenomenal later in
west."
How high is "phenomenal"?
"Phenomenal" is defined as a significant height of more than 14 metres. This
implies occasional individual waves up to 22-25 metres (70-80 feet).
Not a good time to be at sea though I have to admit that I enjoyed a really
good storm when I worked on the Ocean Weather Ships :-)
--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org