Weather for a charter week

On a charter, the weather decides more than anything else: where you go, when you leave and where you spend the night. This lesson shows how to read a forecast, where to find one, and which local winds to watch for in our sailing areas. And it shows when the right answer is to stay put.

A forecast gives the wind direction, its strength and the gusts. The direction is where the wind blows from, so a northerly blows from the north towards the south. Strength comes in knots, or as a force on the Beaufort scale. Force four is eleven to sixteen knots, a pleasant sailing breeze, and force six is twenty-two to twenty-seven, a strong breeze with white crests everywhere. Force eight, from thirty-four to forty knots, is a gale. Gusts can be a third or more above the mean, and much more off high land, so reef for the gusts, not the average.

Check at least two sources, morning and evening. The national weather service gives the official forecast for the coast, often in Beaufort forces. Apps show the computer models in knots, hour by hour, but they smooth out the gusts and the local effects. Marinas pin the forecast on the noticeboard, and the charter base briefs you before you leave. On the radio, coast stations read forecasts and warnings at set times, announced on channel sixteen of the VHF.

In settled summer weather, the wind follows a daily pattern. Mornings are often calm, with a light breeze off the land. As the land heats up, a sea breeze sets in from late morning, blowing onshore, and builds through the afternoon, often to force three to five. It dies away around sunset, and the night is usually quiet. In Croatia this afternoon breeze is the maestral, and in the Ionian it is the maistro, both from the north-west. So plan the longer legs for the breeze, and the night in a bay that is sheltered from it.

In the Aegean, the summer wind is the meltemi, a northerly that blows from about June to September, strongest in July and August. It often blows force four to six, sometimes seven or more, for days at a time under clear blue skies. It is usually strongest in the afternoon and can ease at night, but not always. It kicks up a short, steep sea, and sends a swell into harbours and bays that face north. The Saronic Gulf, near Athens, is partly sheltered from it, which is why it suits a first charter.

In the Adriatic, two winds change plans. The bora is a cold north-easterly that falls off the mountains, and it can arrive suddenly, even under a clear sky. Its gusts are violent, far above the mean, so when a bora is forecast, stay in a safe harbour or a bay sheltered from the north-east. A cap of cloud along the mountain tops often comes first. The jugo is the opposite: a warm, humid south-easterly that builds slowly over a day or two. It brings cloud and rain, and a long, heavy sea that rolls into harbours open to the south.

The mistral is a cold, dry north-westerly that blows down the Rhône valley into the Gulf of Lion. It reaches Corsica and Sardinia, where the Sardinians call it the maestrale, and it can blow force six or more for several days. It funnels through the Strait of Bonifacio, between the two islands, often a force or two stronger than out at sea. When it is forecast, stay in a good harbour such as Calvi or Ajaccio, or on the sheltered side of the islands.

In the Caribbean, the trade wind blows from the east almost all year, usually fifteen to twenty knots. Around Christmas it often blows harder for days, and short rain squalls bring gusts well above the mean. The hurricane season runs from June to November, and charter companies have their own rules for it. In the Seychelles, the south-east trade wind blows from May to October, and the north-west monsoon from December to March, with calmer months between. In Thailand, the dry north-east monsoon from November to April is the sailing season, and the south-west monsoon brings rain and swell for the rest of the year. So the season you book decides the wind you get.

The best charter skippers are the ones who know when not to go. Read the whole forecast: the wind, the gusts, the direction, and how it changes tonight and tomorrow. Then ask what the worst is, when it comes, and where you will be at the time. If the forecast is beyond your crew or the boat, stay in harbour, or make a short hop downwind to somewhere safer. Check the night's shelter against tonight's wind, not this morning's. A day ashore is part of the holiday, but a rough passage with a frightened crew is not. Next, the plotter, the apps and the week's plan.