James Trelawney
Why the old ways still hold true
Coastal sailing around the British Isles has always demanded a keen eye on the sky. Official forecasts are invaluable, but they cover large sea areas and are issued hours apart. Between updates, the weather can shift dramatically – a sea breeze kicks in, a squall line races across the bay, or fog rolls in from the Channel. Long before shipping forecasts were broadcast, fishermen, ferrymen and yachtsmen read the clouds, the wind and the glass to decide whether to put to sea. That heritage of observation is not folklore. It is practical seamanship, and it remains the best local forecast you will ever get.
Learning to interpret natural signs takes time, but it sharpens every trip. You begin to notice patterns that a blanket forecast cannot capture: the way the wind backs before rain, the sudden stillness that precedes a gust, or the greasy look of the sea when a swell is building. This article is a gentle guide to the signs I trust most before casting off from a harbour or mooring.
Cloud patterns that warn of change
Clouds are the sky’s handwriting. A few minutes studying them can tell you more about the next six hours than a glance at a phone screen.
- Mackerel sky – rippled, dappled altocumulus. Often a sign of a warm front approaching. The old rhyme says, “Mackerel sky, mackerel sky, never long wet, never long dry.” Expect a change within 12 to 24 hours, frequently rain and freshening wind.
- Inky cumulonimbus – towering anvils with dark, flat bases. These bring squalls, hail and violent gusts. If you see one building upwind, reef early or stay put.
- Cirrus thickening – wispy hooks high up, spreading into a veil. This is the leading edge of a warm front. The barometer will start to fall, and wind will back and strengthen. You have perhaps six to twelve hours before rain arrives.
- Fog banks – low, soft-edged cloud over the sea, often with a hazy horizon. In spring and early summer, warm air over cold water can produce sea fog in minutes. If the horizon loses its sharp line, expect visibility to drop.
Look also at the colour of the sky at dawn and dusk. A red sky at night really can mean high pressure and fine weather to come, especially if the horizon is clear. A red sky in the morning often means a front has passed and unsettled weather is on its way.
Wind shifts and the coastal breeze
Along the coast, wind is rarely steady. It bends around headlands, funnels through estuaries and reverses with the daily heating of the land. The classic sea breeze is a gift and a warning. On a warm summer day, the land heats faster than the sea, drawing cooler air inland. By late morning, a gentle onshore breeze may build to force 3 or 4. It can turn a flat calm into a pleasant sail, but it also brings a sharp chop and can oppose an ebbing tide, making a nasty sea at harbour mouths.
Watch for catspaws – dark, ruffled patches racing across the water. They show where gusts are hitting. If the catspaws change direction, the wind is shifting. A backing wind (anti-clockwise, e.g. from south-west to south) often precedes foul weather. A veering wind (clockwise) usually follows a front and brings clearer conditions. Feel the wind on your neck, check a burgee or telltale, and note the direction every half hour. A sudden drop in wind strength, then a quick flick in the opposite direction, means a squall is on you.
The barometer’s slow counsel
A barometer is the sailor’s most honest instrument. It does not shout, but it never lies. What matters is not the absolute reading but the rate of change. A steady glass around 1015–1025 hPa means settled weather. A slow fall over several hours warns of an approaching depression – usually with wind and rain. A rapid fall of more than 3 hPa in three hours is a serious signal: batten down, reef deeply, or stay in port.
A rising glass after a storm indicates clearing weather, though the wind may veer and blow hard for a while. If the glass rises quickly after a deep low, expect squally, showery conditions. Tap the barometer gently and note the trend. Combine that with the feel of the air: a sudden drop in temperature or a rise in humidity often precedes rain by an hour or two. The old saying “when the glass falls, look to your mooring” is sound advice.
A pre-departure ritual
Before any coastal trip, I follow a simple routine that blends modern forecasts with natural signs. It takes five minutes and has saved me more than once.
- Check the official forecast for your area, but treat it as a starting point, not gospel.
- Read the barometer and note the trend over the last three hours. Write it down if you keep a log.
- Step outside and look up. Identify cloud types, estimate cover, and watch for thickening or towering.
- Feel the wind on both cheeks. Is it steady or gusty? Does it match the forecast direction? Check a flag, tree or moored boat.
- Look at the sea. Is there a swell running? Are there whitecaps beyond the shelter of the harbour wall? Is the horizon sharp or hazy?
- Listen and smell. A sudden stillness, a drop in bird activity, or the smell of rain on the wind are all clues.
If the signs disagree with the forecast, trust your senses – they are local, immediate and specific to your patch of coast.
The sailor’s balance
Reading weather signs is not about abandoning forecasts. It is about layering your own observations on top of them. Every harbour has its own microclimate: the way wind accelerates around a headland, the fog that creeps up an estuary, the sea breeze that arrives like clockwork at 11am. Learning those patterns is part of the heritage of coastal sailing, passed down from generations who had no radio and no internet. Keep a notebook, note what you see, and compare it with what happens. Over a season, you will develop an instinct that no app can replace. Then, when the glass starts to fall and the cirrus thickens, you will know exactly what to do – reef early, shorten sail, or simply enjoy a perfect afternoon on the water, confident that you read the signs correctly.
