Thunderstorms, squalls and lightning
Emergencies · Power & sail
Thunderstorms and squalls bring sudden violent gusts, wind shifts, lightning, blinding rain and sometimes waterspouts. The best defense is not being out in them: watch the forecast and the sky, head for shelter early, and know what to do if one catches you.
Safety first
- Gusts of 34 kt or more, the Special Marine Warning level, are often strong enough to capsize small boats, especially when they arrive without warning.
- A lightning strike can be catastrophic, starting a fire or knocking out electronics. After a strike, check everyone aboard and look for fire.
- Squalls can cut visibility to almost nothing in seconds. Slow down before the rain arrives.
Before and while you're out
- If thunderstorms are forecast, the NWS advice is simply not to go out. They form quickly, and a boat may not be able to reach port in time.
- There are no specific warnings for lightning, but every thunderstorm produces it. Special Marine Warnings cover storm winds of 34 kt or more, large hail and waterspouts; keep NOAA Weather Radio on.
- Watch the sky: tall clouds with anvil-shaped tops, dark threatening clouds, and squall lines ahead of cold fronts. A steady rise in wind or seas is another warning sign.
- Count from flash to thunder: every five seconds is about a mile. If you can hear thunder you are likely within striking distance, and lightning can strike miles ahead of a storm and after it seems to have passed.
When a storm is coming
- Head for port or shelter early, well ahead of the storm. Thunderstorms are usually brief, so waiting one out ashore beats riding it out.
- Get everyone into life jackets. Secure loose gear, hatches and ports, fix your position and work out the best course to shelter, and keep a sharp lookout for other boats and obstructions.
- Take the first, heaviest gusts on the bow rather than on the beam; heading into the wind is the most seaworthy attitude for most small boats. Meet the waves at about 45 degrees.
- On a sailboat, reef or take sail down before the squall arrives; the first gusts are usually the strongest.
- If you can't reach shelter, the NWS suggests anchoring if you can and getting as low as possible.
- Heavy rain counts as restricted visibility under the Rules: slow down, show your lights and sound fog signals (Rule 35).
Lightning aboard
- Most lightning deaths and injuries on boats happen on small open boats. Larger boats with cabins, especially with a properly installed lightning protection system, are relatively safe if you stay inside.
- Stay inside the cabin, in the center if you can, and away from metal and electrical equipment. In an open boat, stay low and keep arms and legs out of the water. Don't touch two grounded objects at once.
- The NWS and BoatUS advise unplugging electronics, including radios, during the storm, and lowering or tying down antennas that are not part of a lightning protection system. Decide beforehand how you would call for help while the VHF is disconnected.
- Wait 30 minutes after the last thunder before going back to normal activity on deck.
Waterspouts
- A waterspout is in effect a tornado over water. Never go closer to look. The NWS office in Melbourne, Florida advises moving away at a right angle to its apparent direction of travel.
Sources (9)
weather.gov · weather.gov · weather.gov · weather.gov · boatus.org · weather.gov · weather.gov · navcen.uscg.gov · rya.org.uk
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.