On Tuesday, September 22, 2020 at 11:46:24 AM UTC+1, N_Cook wrote:
On 22/09/2020 11:28, Graham Easterling wrote:
On Tuesday, September 22, 2020 at 11:20:01 AM UTC+1, Norman Lynagh wrote:
Graham Easterling wrote:

The weekend saw the highest astronomical tide of the year. However,
it was even higher than predicted, and still is running above
predictions.

https://www.ntslf.org/data/realtime?port=Newlyn

This is despite all the weather and sea conditions suggesting it
should be below predictions. The local weather light winds (basically
calm yesterday), fairly high barometric pressure. Local sea
conditions, flat in Mount's Bay. Atlantic swell very small, so no
wave setup surges. In fact, all the factors which increase tidal
height were absent, all the normal factors which reduce it were
present. I'd expected it to be 0.3-0.5m below predictions.

I was down at the Battery Rocks for a swim yesterday, and got
chatting to a chap who had been a year long swimmer there most of his
life. He'd never seen the tide so high in totally benign conditions.

No I'm baffled, as was the chap I spoke to, & I respect the opinion
of people with his sort of observational experience. Mind you the sea
is a mysterious thing.

Graham
Penzance

Sea level rise? Perhaps only apparent in calm conditions.

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

I don't think it's the whole story, experience has shown me that under recent conditions the actual tide is normally below predictions.

Mind you, over recent decades there has been a rise at Newlyn, which is supposed to be a stable site. (Though Scilly is sinking)

A study on sea level at Newlyn here
https://www.tandfonline.com/doi/full...ean%20w aters.

I can only assume that some weather event elsewhere in the north Atlantic has caused a 'dome' of water which has proved persistent.

Graham
Penzance


Although NTSLF uses supercomputer oceanographic processing of the first
pass MetO data, there are problems with it by the time it is output , if
not before.
Notoriously , www presentation so of no significance the likes of 07:60
instead of 08:00 for timings on their outputs.
Of more significance , if you look carefully at the archives, assuming
the same for Newlyn as for Southampton.
Coincident with change-over times of BST/GMT, over the week before and
after, there is a vertical "DC" offset in the mean sea level of about
0.15m, there until the next clocks change.
Unfortunately al loceanographic major processing uses Fortran still and
the people who developed the NTSLF tide predictor SW have retired, so mo
one to rectify its failings.
For Southampton it regularly fails to predict surges from the SSW, ie
wind that goes behind the Brest Peninsular and wind-stresses the water
betweem St Brieuc and IoW, worst case failing to predict about 0.8m surge..



--
Global sea level rise to 2100 from curve-fitted existing altimetry data
http://diverse.4mg.com/slr.htm

As I mentioned on UK Weather and Climate group, the unusual high tides, above astronomcal, timed at spring tide are probably a bit of extra swell. Maybe from the rather numerous Atantic hurricanes. The forecast models don't cope well with rogue waves nevermind rogue swells. Non linear interactions, unusual wave trains and all that. Notice the amplitudes are the same as astronomical.

Len
Wembury