Have a good look at the picture above. I took it during a night walk along the Brighton seafront.
If I was planning to set sail the following morning, what clues and signs should I take note of in this scene?
I’m sure you spotted the mares’ tails. These sharply curved cirrus clouds indicate moisture in the upper troposphere and wind shear; two things we see before a front goes through. They are a sign of bad weather on the way.
But did you spy the sliver of a very young moon low in the sky?
It is very unusual to spot a moon this young in a city. It is common sight in deserts and oceans, far from light pollution, but it was a rare treat to see it above the bright lights of the buzzing pier.
This moon is not even 48 hours old. It can be used to navigate, although the method is less reliable when the crescent is this low.
But this moon is a cast iron clue to one thing: big tides.
The crescent is in the western sky and bright on its western side, which tells us that it is a waxing moon. A waxing crescent this thin means that we are in spring tides, the largest tidal range.
Spring tides bring the biggest ranges in tidal height – the sea goes up and down its maximum amount at these times – but it also leads to maximum horizontal flows, ie. fast currents or streams.
Storm force winds and fast moving water: a nasty combination for any boat!
Sailors of old would have taken one look at the scene above and prayed for another day in port.
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