Sailors in coastal waters say that when the tide changes, more often than not the wind direction changes too. What links these two events, one of which is astronomical and the other meteorological?
鈥� There may be an easy explanation for the observations.
There are many places around the UK and elsewhere with fast-flowing tidal currents, which also have a large population of sailing vessels.
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Consider the impact of the tide on airflow measured on board a vessel bobbing in such areas. When the tide is going out at 3 knots, for example, and the there is a 3-knot wind moving in the same direction, there will be no wind felt on deck. But if the tide changes direction and the wind does not, you will then feel a 6-knot breeze on the deck.
The wind has not changed in relation to the land and seabed but, as far as the sailing boats are concerned, the wind has indeed been influenced by the tide.
Graham Cox
鈥� There are several reasons why sailors think the winds change with the tides. When the wind blows against the direction of the tide, it can make waves steeper than when air and water are moving the same way. This slows the yacht down. So a change in tide makes it seem as if the wind strength has altered, even when the change in apparent wind is small.
Tidal changes may often occur in the morning or evening and so coincide with the onset of a 鈥渟ea breeze鈥� or a 鈥渓and breeze鈥�, caused by the warming and cooling of the land on sunny days. Sailors, who are often longing for a wind shift, may associate this weather phenomenon with the tide.
Max Wilkinson, Dedham, Essex, UK
鈥� As a sailor of coastal waters for some 40 years, I have to tell your questioner that their scepticism is correct 鈥� there is no connection between tide and wind direction. Tidal direction changes four times over an approximately 24.5 hour cycle, but the wind does not. What one can say with absolute certainty is that if the wind direction changes, the tide will have changed at some point in the previous 6.5 hours.
Beware that sailors are also likely to tell you about mermaids, and refuse to wear green while at sea.
Vincent Lugthart, London, UK