A table of standard port values for cadastral purposes is available on this website - see 'Related content' below. This table is not intended to be used for the determination of cadastral or administrative boundaries.These predictions used the harmonic constituents derived from the analysis of the observations made at that port during the period given in the table on the 'Standard port periods of observation' page. As you can see on the tide chart, the highest tide of 5m will be at 4:44pm and the lowest tide of 1.6m will be at 11:08pm. The values for HAT and LAT are the highest and lowest tidal levels predicted to occur under average meteorological conditions during the period 1 January 2000 to 31 December 2018. The tide is currently rising in Devonport.The value of MSL has been derived from the analysis of tidal observations made at the port during the period given in the table on the 'Standard port periods of observation' page.There is annual variation of the tidal levels, so the variation in the ranges of the spring and neap tides over the 19-year cycle is twice that of the levels. The values for the spring and neap ranges have been deduced from the spring and neap tidal level values.This variation is in the order of up to 0.15 metres. The average annual value of tidal levels vary from year to year in a cycle of approximately 19 years. These predictions used the harmonic constituents derived from the analysis of the observations made at that port during the period given on the 'Standard port periods of observation' page. Large coefficients indicate important high and low tides major currents and movements usually take place on the sea bed. The values for the MHWS, MHWN, MLWN and MLWS tidal levels are the averages of the levels of all spring and neap tides predicted for the period 1 July 2023 to 30 June 2024. The following graph shows the progression of the tidal coefficient in the month of November of 2023.These values give us a rough idea of the tidal amplitude in Plymouth (Devonport), forecast in November.The levels, in metres, are referred to chart datum, which is the same as the zero of the tidal predictions in all cases.Changes in level due to barometric pressure seldom exceed 0.3m but, when mean sea level is raised or lowered by strong winds or by Storm Surges (wind-induced long period waves causing higher and lower-than-predicted levels to occur), this effect can be important. The water level does not, however, adjust itself immediately to a change of pressure and it responds, moreover, to the average change in pressure over a considerable area. A low barometer will tend to raise sea level and a high barometer will tend to depress it. In extreme conditions the wind can set up a storm surge, which when combined with a high spring tide can dramatically increase the height of tide actually experienced.Ĭhanges in Barometric pressure cause the sea level to rise, a difference of 34 millibars from the average can cause a difference in height of about 0.3m. Winds blowing along the coast may advance or retard the time of High Water. Onshore winds will pile the water up on the coast and offshore winds will have the opposite effect. The graph below shows the tide heights for Plymouth (Devonport) over the next seven days. Please note that predicted tidal times and heights are representative of average meteorological conditions and can differ significantly from the actual tide time and height due to the local meteorological conditions. This information includes: Predictions for high and low water for each day of the year for all Standard Ports. computed values and they are in metres above Chart Datum which is the zero point or reference plane from which the tidal heights are measured as defined above. Australian National Tide Tables (ANTT) contains information for over 80 Primary (Standard) 1 and 600 Secondary 2 ports in Australia, Papua New Guinea, Solomon Islands, Antarctica and Timor-Leste. The specific phrase "Predicted heights are in metres above chart datum" means that the tidal heights are predicted i.e. Where this gap is at its greatest, this is a Spring Tide. Where the change between high tide and low tide is at its smallest a Neap Tide has occurred. LAT is not an extreme level, as storm surges may cause considerably lower levels to occur. The graph below shows the tide heights for Plymouth (Devonport) over the next seven days. LAT is the lowest level which can be expected to be predicted under average meteorological conditions and under any combination of astronomical conditions this level will not be reached every year. In the United Kingdom, this level is normally approximately the level of Lowest Astronomical Tide (LAT). By international agreement it is defined as being a level so low that the tide will not frequently fall below it. It is also the plane below which all depths are published on a navigational chart, so that adding the tidal height to the charted depth the true depth of water is determined. Chart Datum is the plane to which all tidal heights are referred.
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