HotRIBS - The online RIB Magazine
 
 
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  #034
04. Reading The Isobars
All extracts courtesy of the MarineCall Guide
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  Wind direction

The direction of the wind is determined by the fact that the wind blows around a depression leaving it to the left and will avoid an anticyclone leaving it to the right (Northern Hemisphere).

If the centre of the depression passes to the north of an observer, the wind veers from the south to south-west, then to the north west.

If the centre of a depression passes to the south of an observer they will notice the wind backing from south-east to east to north-east.

Many weather maps have a scale in one corner called the 'Geostrophic Scale'. Using a pair of dividers, take the distance between adjacent isobars over the area of interest and read off the wind speed for the appropriate latitude on the Geostrophic Scale.

It is important to appreciate that for a given isobar spacing, the wind is much stronger in low latitudes compared to high latitudes.