How do sailors know a storm is coming?

There are a number of ways sailors can learn about an approaching storm.

  • Weather forecast. With a satellite data connection, sailors have access to up-to-date weather forecasts anywhere in the world. Although forecast accuracy decreases in relation to how far into the future the forecast looks, current forecasting capabilities are quite good and can give a sailor several days’ advance notice of a coming storm. A tool like the Weathermuffin app can proactively alert sailors to upcoming adverse or uncomfortable conditions.
  • Weather fax. With some simple equipment, weather charts and satellite imagery are freely available to sailors via radio. Synoptic weather charts and forecasts depict the locations (and anticipated movement) of low pressure systems, fronts, and cyclonic storms. Satellite imagery shows fronts, cyclonic storms, and squall activity.
  • Weather router. An excellent resource is a weather router, which is often an experienced and professional meteorologist who will provide one-on-one service to help with planning, watch the weather, and alert about upcoming conditions. This may be an attractive option because not only will a sailor benefit from their expertise, but also a router typically has access to more and higher fidelity data to interpret. Ideally the weather router has sailing experience and understands how conditions affect boat operation, comfort, and safety.
  • Designated person ashore. A sailor can designate a knowledgeable and responsible person on land to help watch the weather. This requires an offshore communication setup, such as satellite data, satphone, Garmin InReach, SSB radio, etc.
  • VHF weather radio. If a sailor is within range of the VHF WX (weather) stations broadcast in the U.S., basic voice forecasts are available.
  • 500 MB. Upper air observations and forecasts—in particular for the 500 millibar pressure contour—can be used by advanced mariners to make educated guesses about storm system genesis and progress. For details see the book Heavy Weather Avoidance and Route Design by Ma-Li Chen and Lee S. Chesneau.
  • Barometric pressure. A barometer—or even better, a digital barograph—is a vital observation tool. Rapidly falling pressure can indicate a forming or approaching low pressure system.
  • Wind shifts. If the wind rapidly changes strength or especially direction, the forming or approaching of a low pressure system may be indicated. Buys-Ballot’s law may be used to estimate the bearing of the system.
  • Clouds. Learning to “read” the sky is a valuable and rewarding skill. Recognizing an approaching warm front will help a sailor prepare (especially for those followed closely by a cold front), as will sighting a row of cumulonimbus clouds on the horizon.
  • Radar. Because water droplets reflect radar, it’s a valuable tool for observing squalls, especially on dark nights.
  • Temperature. If the temperature is observed to change rapidly, it could be due to a front.
  • Change in sea state. Because ocean waves travel faster than storms, if a new swell is observed, it could indicate a strong wind or storm in the distance.

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