Possible Storm Surge Tuesday

Hydrozoan said:
But dennyjc has calculated ~5.3 maximum this time, and has posted data showing ~5.6m in December (and I confirm both figures).

That's a difference of about 0.3m between now and then, rather than the difference of about 0.65m pvb got from the Environment Agency data.

Does anyone know how that difference arises, I ask (again)?
Click to expand...

Hello,
My first graph is just a prediction
It uses a tidal prediction and adds a surge prediction so please don't hold it up to too close a scrutiny
Already the surge prediction has been modified (since the data I used)
and suggests the ultimate height of water will be a bit less than originally feared

But we'll not know until after the event
 
dennyjc said:
Hello,
My first graph is just a prediction
It uses a tidal prediction and adds a surge prediction so please don't hold it up to too close a scrutiny
Already the surge prediction has been modified (since the data I used)
and suggests the ultimate height of water will be a bit less than originally feared

But we'll not know until after the event
Click to expand...

Thanks. Yes, I understand that your first graph is just a prediction. I did essentially the same calculation, from the same data sources, and agree with you. (I also remembered - all too well! - the nail biting last December and how it came up to the eventual height of 5.6m which you had then highlighted as the level of concern at Shotley.)

But what puzzles me is set out in my post #46. I pointed out there that the difference between (1) the predicted maximum height today that you and I have estimated and (2) that obtained from the Environment Agency data which sailorman and pvb were discussing (posts #36 and #39) could not be entirely explained by differences in the predicted surge and by the Felixstowe-Harwich CD difference.

It seems to me that both sets of calculations have been made correctly, but a difference of about 0.35m remains, and I continue to wonder why.

(I don’t think it alters the fact that this time looks, so far anyway, less serious in the Harwich area than last December - because the peak surge and HW are less in sync - but the difference between the two approaches still puzzles me.)

Added for clarification. The Environment Agency says that: "We are expecting high tide levels due to a combination of a tidal surge and high winds. We are expecting to issue this alert again for Wednesday morning's tide. The forecast high water is due at Harwich at 11:30pm on 21st October 2014. The predicted astronomical tide level is 1.89 m AODN. The forecast surge height is 0.91 m. The forecast tide level is 2.8 m AODN. The forecast wind direction is West North West. The forecast wind strength is force 7. mAODN is a standard measure used across the UK for height above average sea level. It is different to Chart Datum. We will continue to monitor levels closely and update this message as necessary. 11:25 on 21 Oct 2014"

Adding about 2m for the Harwich (-2.02m) or Felixstowe (1.95m) CD/ODN difference (as pvb suggested in #39) takes the 'forecast tide level' to about 4.8m, quite a bit less than 5.3m despite the surge forecast at 0.91m being similar to that (~1m) forecast for HW Felixstowe by the NTSLF.
 
Last edited:
dennyjc said:
Hello,
My first graph is just a prediction
It uses a tidal prediction and adds a surge prediction so please don't hold it up to too close a scrutiny
Already the surge prediction has been modified (since the data I used)
and suggests the ultimate height of water will be a bit less than originally feared

But we'll not know until after the event
Click to expand...

Nice work Colin :encouragement:
 
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