Pressure and wind map from XCWeather

Met Office Charts

Met Office Latest Observations (Text)

Back to Map

This page uses the publically available tidal data from POL (Proudman Oceanographic laboratory) and presents it in graphical form. It is most useful for trying to understand how the tides move around Britain and the presence and movement of surges.

Note that this data has not been error corrected. This site comes with no guarantees! It simply tries to present the available data in an understandable way - but if you need data for any serious purpose then you should go directly to POL and other such organisations.

The levels on the POL site are measured every 15 minutes and may be 30 minutes out of date. It is reasonable to wonder how from that this site is updated every 5 minutes! The answer is that POL also provide the predicted curve - so having found the most recent measurement and the predicted level at that time - that gives a surge figure which can then be applied to the predicted figure at the current time - yielding the most accurate up to date figure possible. However it should be born in mind that the surge figures may well be 30 minutes out of date. Because of this method of updating there is a problem around midnight which remains as an issue to be solved ...

Because of the time delays this is not a suitable site for indicating or observing tsunami.

On the map next to the coast is a scarlet or green line representing the current surge at this point. Outside this may be a blue line - this represents the tidal state at this moment (NOT THE HEIGHT). ie the thickest line represents High Water (regardless of at what height that is) and no line at all represents Low Water. NB to avoid a very misleading view Port Ellen with its unusual low range of tides does not have a blue line at all.

In the three day graphs for each section the level is indicated by a line which will be red for positive surge and green for negative surge. If red the top of the thickness of the line is the actual measured level and the bottom is the predicted level. If green the top is the predicted level and the bottom is the measured level. The surge is thus shown by the thickness of the line. Any missing data will be shown by a yellow line which should indicate the predicted level - however errors may result in anomalous results which should be obvious. (If you think you have detected a tsunami the chances are you have found an error!)

The POL Surge prediction links will ask for your email address and password the first time you click - register if you have not done so already (free) - after that you will be taken straight to the graph required.

The tidal 'clocks' on the map indicate the expected situation according to tidetables. They run clockwise: High water at '12 o'clock'; half tide, falling at 3 o'clock; Low Water at 6 o'clock; half tide rising at 9 o'clock. Red for rising tide, green for falling tide. Note that the general movement of the tide around Great Britain is clockwise with the exceptions of the South Coast of England and the South Coast of Wales.

DESCRIPTION: THE TIDES OF GREAT BRITAIN

Tides appear to circle around points of zero tide (amphidromic points), anti-clockwise in the northern hemisphere, and the heights are more or less proportional to the distances from that point.


The major North Atlantic amphidromic point is about two thirds of the way towards America going west from Cornwall. The semidiurnal tidal wave from the tip of South Africa comes north up the west coast of Africa and joins with the eastern side of the North Atlantic circulation. It passes the tip of west Africa and two hours later it reaches the south of Spain and an hour after that passes the north of Spain. About an hour after that it first reaches St Mary's and Newlyn on the South west tip of Britain. It has been building in height and at the Uk is some three times higher than when it first reached the tip of west Africa.

The 'wedge' of Cornwall divides the wave. It continues east along the south coast. However in the Northern hemisphere waves tend to the right resulting in much lower tides on the English coast and much higher on the French coast. In the centre of the South coast is a minor amphidromic point where the tide 'breaks away' from the coast, resulting in the much lower range 'double tide' section from Weymouth to Portsmouth. This section marks the furthest point influenced also by the tide which has come down the North Sea which is the Atlantic tide (as at St Mary's) delayed by about two and a half wavelengths. The South coast tide is about a half wavelength from west to east and therefore at the meeting point more or less at Dover the two tides which have come by two different tidal routes are roughly in phase. The area of meeting of the two tides stretches from the Isle of Wight right round to the coast of Suffolk where its last influence is seen at Lowestoft.

The tide along the North Cornwall Coast, keeping right, is much higher and it swings into the Severn Estuary, building as it goes until it becomes the highest tide of British shores and almost in the world. It sometimes results in the Severn bore.

As it runs into the Severn estuary it also comes east along the South coast of Wales. Note therefore that the tides of Great Britain all run clockwise with the two exceptions of the South Coast from St Mary's to Dover and the South Coast of Wales from Milford Haven to Avonmouth.

The tide runs north into the Irish Sea, past the west coast of Wales, swinging right to give a high range of tide at Liverpool. The tides on the Irish coast of the North Sea are much lower in height. At the exit of the Irish sea to the north the tide is effectively blocked not just by the narrowness of the channel but also because it is well out of phase with the Atlantic tidal wave coming north of Ireland. It will be seen the the tide at Port Ellen is very small and frequently unstable.

The Atlantic tide reaches Tobermory on the west coast of Scotland. It sweeps around the north of Scotland and breaking away from the Atlantic circulation, keeping right turns south and comes down the east coast. By the time it reaches Dover it meets the direct tide from the south coast. The wave form at Dover sometimes shows the 'stress' that is caused by the merging of these two waves with differing phases. The time from Low to High Water is at times only half what it is from High water to Low water.

The amphidromic points significant to Great Britain are therefore:
The major North Atlantic circulation;
The minor amphidromic point near the New Forest in the centre of the South Coast of England;
The minor amphidromic point in the narrow channel between Ireland and Scotland;
The amphidromic point on the south western coast of Norway around which the tides of the northern part of the North Sea revolve;
The amphidromic point in the centre of the North Sea;
And the amphidromic point in the Southern North Sea.


In the Southern North Sea the tide coming down the east Coast meets the tide coming past Dover which helps to 'turn it' across the channel so that it proceeds north up the Belgian and Dutch Coasts before swinging across towards Cromer to reinforce the next tide coming down the east coast.