Coastal weather in the summer

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  • Children playing on the beach. Photo: Anthony Devlin/PA Wire

    Braving the elements at Broadstairs, Kent. Photo: Gareth Fuller/PA Wire

    Barrafundle beach, Pembrokeshire. Photo: David Davies/PA Wire

    Weston-super-mare, Somerset. Photo: Tim Ireland/PA Wire

  • Coastal weather in the summer
    30.07.2011 15:38

    With the summer holidays having recently started, many people in Britain will be thinking of taking a trip to the beach. The weather in coastal areas in the UK can differ quite markedly at times from that experienced further inland and this is particularly the case during spring and summer.

    The most significant and obvious feature of coastal weather at this time of year is the sea breeze. This forms during the day when there is a fair amount of sunshine. As the land warms quicker than the sea, the resultant difference in temperature results in the air over the sea becoming colder and denser than that of the land. Consequently, there will be an increasing likelihood of this cool and dense air overriding the warmer and lighter air inland. 

    The resultant change in wind direction is known as the sea breeze. It can occur from around mid morning to late afternoon, but is generally around its strongest in mid afternoon. The sea breeze does not always form. If the weather is cloudy, then there will be little difference in temperature between the land and the sea and hence the sea breeze will not form. If the prevailing wind is a brisk offshore wind, then although the sea breeze will still usually form, the prevailing wind will prevent it from reaching land. Very occasionally, in exceptionally warm conditions, the air in the lower levels of the atmosphere is so warm, even over the sea, that there is not the temperature differential to generate the sea breeze.

    The next most obvious feature of coastal weather is there is generally more sunshine than further inland. This is because the air over the sea in summer is much more stable than that inland, which makes it less conducive to cloud formation. So if the wind is onshore, then the weather along the coast may be sunny, but there may be a fairly substantial build up of cloud inland. For the same reason, this means that coastal areas are also more likely to escape showers during the summer. 

    The sunniest places in the UK are (in order) found in the Channel Isles, the Isle of Wight and a long stretch of coastline from around Dorset eastwards to Kent and Essex. Here, sunshine totals generally average more than 7 hours a day through the summer months and are near 8 hours a day in places. This all adds to the attraction of going to the coast. It may be cooler than inland, but if there is more sun, then there will be more opportunity for some sunbathing. 

    The other main feature of coastal weather is fog and low cloud. This is caused by a warm airmass crossing the sea. As the air cools, it may cool to the appoint at which it becomes saturated. When this happens then fog or low cloud can form. Although this can spread a long way inland overnight, it usually quickly burns back to the coast during the morning. However, the fog and low cloud can prove remarkably stubborn even in summer to fully disappear and it is on these occasions that coastal areas can be very disappointing. An excellent example is from July 1983. This was an exceptionally warm month over much of the UK. However, the east coast of England was plagued by several days of low cloud while coastal areas elsewhere were baked in warm sunshine.

    The east coast is generally not the best place to go for very high temperatures in summer. This is because when the wind is westerly and thus offshore, the air mass is often relatively cool as it has come from the Atlantic. This will also result in bands of cloud and rain moving eastwards at times. Hot days can occur along the east coast but they tend to be only occasional and usually one off days ahead of an approaching front. However, with the right weather situation, coastal areas in the south and west can experience consecutive days of very warm or hot weather. The months of July 1983 and August 1995 were dominated by high pressure and hence were very settled. But the wind direction was usually from the east or northeast, coming off a warm continent. Thus some coastal areas along English Channel and Irish Sea coasts had a remarkably warm month, with maximum temperatures around 5-6C warmer than usual, giving these areas a taste of the Mediterranean!

    By: Tony Conlan