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   MMBFC Home      Weather & Tides      Tide Information

Weather Front Animation:
 Click the graphic to run the animation
This Flash animation relates how precipitation and clouds form along cold and warm fronts. For the cold front, cooler air advances upon warmer air, forcing the less dense warm air upward. Clouds and precipitation form along the front. The warm front is characterized by warm air advancing upon a wedge of denser, cooler air. High level and then increasingly lower level clouds portend the arrival of the warm front. It should be noted that the towering cumulonimbus clouds pictured in this animation usually don't form in the winter due to insufficient temperature contrasts within the atmosphere. The animation can be paused and rewound to stress important points
Tidal Considerations
It is very important to ensure that your plans for fishing, boat or shore, fit with the tidal predictions for the day of your trip. Most beaches, slipways and launch sites are tidal. Check the times of high and low water and assess how they will affect your trip when you launch and later head for home. If the tide turns to a wind-against tide direction, the sea may become much rougher. Check whether it will be a neap or spring tide. Beware of harbour entrances where tidal currents can be quite severe. For a comprehensive tidal prediction service for Swansea visit Easy Tide link below. Tide tables are also available on this website.


Tidal Variations

It is helpful, but not essential, to understand the reason why the tides vary in height and time on different days. Twice daily, the tide comes in, and each day it will be approximately 50 minutes later than the previous day. Astronomically, this is because as the Earth moves around on its axis every 24 hours, the Moon during the day and night moves through one-thirtieth of its orbit around the Earth. This means that it will be approximately one-thirtieth in a different position 24 hours later.
This, of course, influences the tides because of the importance of its gravitational pull on the world's oceans and seas. The water pull is best visualised as a horizontal movement, not as a vertical up and down movement as viewed from the shore. There is a considerable variation in the height of the tide from week to week.
 Because of its nearness to the Earth, the gravitational pull of the Moon is the stronger influence than that of the Sun. As the Moon orbits around the Earth it exerts its gravitational pull as illustrated
  • Highest Spring Tides - Moon and Sun in conjunction, with combined gravitational pull producing the highest tides. High tides on the opposite side are due to the centrifugal force of the Earth's rotation.
    The highest tides in England occur about two days after the New and Full Moon.
  • Neap Tides - Moon's orbit moves towards 90° to that of the Sun, when they are at quadrature, and their relative pulls, about 7 to 3 in favour of the Moon, result in Neap tides, with smaller variations.Neap tides occur 2 days after the first and third quarter of the moon,when there is least difference between high and low water.
  • Spring Tides - Moon and Sun in opposition, with combined gravitational pull.
  • Neap Tides - Moon's orbit moves toward the quadrature.
The highest spring tides of the year occur after the equinoxes in March and September. However, the weather may not be so good, and rain and gales are frequent. The Tide Tables cannot be relied on for precise highs and lows of the tides. A storm surge out in the Atlantic can put at a metre on a high tide in exceptional circumstances, and the wind can also prevent the tide from receding as much as it should.
It is interesting to note that high spring tides occur at approximately the same time of the day every year in each location on the coast. This means that high springs occur at dawn and dusk in around Mumbles and Swansea.
The configuration of the shore has a large bearing on tide heights and range, tending to increase in bays and funnel-shape inlets like the Bristol Channel.
Bristol Channel Tides
The Bristol Channel has the second largest tide range in the world (Avonmouth 12.3m mean spring tide) there are several factors that have an effect on the tides: The shape of the land, the mass of water to the west (Atlantic Ocean, topography of the land and influential permanent and semi permanent pressure systems.
The shape of the land
The Bristol Channel is shaped like a funnel. As the earth rotates and the area makes its twice daily passages through the tidal bulges (semidiurnal) the mass of water is squashed causing it to increase in both range and rate.
The Atlantic Ocean
The greater the mass of water that influences the area then the greater the tidal range.  As the Atlantic Ocean is directly west of the Bristol Channel it has a great effect not only on the tides but also our weather and climate, the effect on the tide is to increase the range.
Topography of the land
The high ground to the south of the Bristol Channel (Exmoor) and the mountains in south Wales have the effect of a funnelling the prevailing Westerly winds and increasing the speed, as the wind moves across the Sea surface the wind speed increases slightly due to the reduced friction causing another increase in wind speed. Waves are formed and a mass of water will be moved up the Channel causing an increase in tidal range.
Pressure systems
During the summer the most influential pressure system is the Azores high, once established this high pressure system is relatively constant and the high pressure influence will have the result of a decrease in tidal range.  When the Azores high pressure subsides (Autumn) the main influence is from the Atlantic and Polar frontal depressions that track from West to East across the Atlantic having the dual effect of reducing air pressure (increasing tidal range) and moving a body of water eastwards (storm surges) causing an increase in tidal range.
Tidal rates
Spring tide rates of 6 knots can be experienced in the region of Laverock Point and the Rannie Shoal.  The funnelling effect of the land causes the mass of water to accelerate as it travels up the Bristol Channel.  At Lavernock the tide splits (main channel and up to Cardiff Bay) as a result the ebb currents also rejoin at this point, squeezing the body of west going water causing an acceleration and the high flow rates.
Counter currents
The entrance to Barry experiences strong currents at 90 degrees to the entrance to the harbour.  There is a counter current close in the entrance and that has the effect of a SW'ly flow even during NE'ly flow further out (flood tide).  This counter current is a narrower band but stronger during spring tides. The approaches to and the Wrach Channel itself experience strong counter currents, (SW flow) starting as early a 2 hours before High Water.
Tide Prediction Links
UK Hydrographic Office (Fast Tide Predictions for Mumbles)
The world's oceans are in constant flux. Winds and currents move the surface water causing waves. Ocean levels fluctuate daily as the sun, moon and earth interact. As the moon travels around the earth and as they, together, travel around the sun, the combined gravitational forces cause the world's oceans to rise and fall.

Imagine the earth covered completely by water. As the earth spins, this water is balanced evenly on all sides by centrifugal force. The moon has a gravitational pull on this layer of water as it orbits the earth. This pull causes the water to bulge toward the moon. Because the earth is spinning there will be a bulge on the opposite side of the earth as well.
As the earth rotates on its axis, each location on the earth will experience both tidal bulges. The areas of high water levels are high tides and the areas of low levels are low tides. Since the earth and the moon rotate around the sun, there is an added modifying factor.
When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season.
When the sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides.
Tides vary from day to day. As the earth, moon, and sun orbit, their positions constantly shift, causing slightly different gravitational effects.
This causes the tides to occur at slightly different times. Tides also vary from place to place and geographical position determines the level of tide.