Charter know-how · Weather

Weather 3: thunderstorms and squalls

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Summer thunderstorms are usually short, but they can bring sudden strong gusts, a wind shift, heavy rain and lightning. Most of the danger comes from being caught with too much sail up or in the wrong place, so the plan is simple: see it coming, and be ready early.

Signs

Tall, building cumulus clouds over the land in the afternoon, especially with an anvil-shaped top.
A dark, low roll of cloud approaching, sometimes with a line of white water beneath it: the gust front.
Thunder or lightning in the distance, and a sudden drop in temperature.
Forecasts mention instability, convective showers or thunderstorms: take them seriously.

Under sail

Reef or furl early, before the first gusts arrive
Lifejackets on, everyone in the cockpit or below
Hatches closed, loose items stowed
Engine on and ready
Head for open water with room downwind, away from the shore and other boats
Note your position on the plotter in case visibility drops in the rain

At anchor

Expect a wind shift: the squall may come from a direction the anchorage is not sheltered from.
Let out more chain if there is room, start the engine and keep someone on watch until it passes.
Take the dinghy out of the water or tie it short, and close the bimini or reduce windage where you can.

Lightning

Stay below as far as possible and keep away from the mast, the shrouds and large metal fittings.
Do not swim. Keep hands off the wheel and metal rails where you can.
Unplug handheld electronics if it is convenient; keep a handheld VHF and phone in the oven or a dry bag as a backup.

Most summer squalls pass in under an hour. If the forecast shows thunderstorms, plan short hops and be in a secure harbour or anchorage by early afternoon.

General guidance for charter crews. Your charter company's briefing, the boat's own manuals and local rules always come first.

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