Coastal Skipper and Yachtmaster Quiz · Meteorology
Measure the gap between the two isobars and lay it on the geostrophic wind scale from its left-hand end. What wind speed does it give?
Part of a weather chart with two isobars, 1008 and 1012, and a gold arrow marking the gap between them. Below is a geostrophic wind scale drawn to the same size as the chart, with a heavy mark at its left-hand end labelled measure from this end. Reading from left to right, the scale is marked 60, 40, 30, 20, 15 and 10 knots, the marks getting further apart.
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30 knots. The geostrophic scale printed on a weather chart turns isobar spacing into wind speed: the closer the isobars, the stronger the wind, which is why the high speeds are at the short end of the scale. Here the gap reaches the 30 knot mark. The wind at the sea surface is usually a little less than the scale gives and backed from the line of the isobars.
