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Thu, 11 Mar 2010

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SEA TEMP DIFFERENCES AROUND CT

Ever wondered why the ocean temperatures are so cold at Clifton and the Atlantic coastline beaches in summer, while at the same time the waters in False Bay are warm in comparison ?

Actually it is rather a simple explanation. During summer, the dominant wind direction is SE, i.e., the trade winds that blow from the SE towards the NW. The dominant South Easterly wind direction has two consequences :

However, let's first look at the action that the wind performs on the ocean surface. Without getting too theoretical, it is is sufficient to know that when wind blows over an ocean surface, a stress is induced on the ocean surface. In short, this means the wind "pushes" or "pulls" the surface layers of the water along with it. Hence, if we apply this to the Cape Town situation in summer the two consequences are :

FALSE BAY
The direct action of the SE wind is to pile up the warm surface waters along the Peninsula beaches such as Fish Hoek and Muizenberg. Hence water temperatures in summer approach the 22�C (72�F) mark.
ATLANTIC COASTLINE BEACHES
Just the opposite occurs here. The strong SE winds pull all the warm water AWAY from the coast. However, this water has to be replaced. In realitity the warm surface waters are replaced by very cold water from great depths along the Cape Peninsula. This water is usually in the realms of 10-14�C (50-57�F) and is known as "upwelled" water, for it has been "upwelled" from greater depths. This cold water is nutrient rich and is usually very clear and blue. So, the next time you wander off down to Clifton and the water is crystal clear, you can bet your bottom Dollar that it is going to be freezing.....If you think that this is cold, try swimming in the great Lakes of the USA in summer......

Keep in mind that the cold water is the result of the SE wind that has blown over the surface of the ocean for sometime. So whenever the SouthEaster has been howling, you can be guarenteed that the Atlantic coastline beaches are going to have freezing waters....but then the hot bods make up for that shortfall !!!!!

Click to view a larger image
showing the effect of the SE wind
on ocean temperatures

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