Mastering the Sky: Essential Weather Tools for Every Sailor

You can always count on the weather changing. It never ceases to amaze me how many different weather patterns I sail through during a short afternoon sail or on a longer passage. A sailboat is continuously sailing to ever-changing locations. Wind shifts direction or changes velocity. Water depth gets deeper or shallower. Clouds form overhead. Wave patterns change with tidal currents.

For all these reasons and more, sailors need to be aware of the weather. Before heading out and once underway, keep an eye on the weather patterns. Early preparation and continuous observations will help prevent any weather-related problems.

Weather forecasts these days are generally reliable and updated frequently, but before satellite technology and advanced radar, sailors dealt with the weather as it arrived. Some of our old-school  weather instruments are still useful today, including the barometer.

An aneroid barometer is a simple instrument to use on a sailboat. A needle on a cylindrical dial will move as air pressure changes. A decreasing air pressure will move the needle toward “rain,” while a rising air pressure will move the needle toward “fair” weather. A barometer will give an accurate change in weather tendency over a three-hour period.

I subscribe to more modern tools online, too: PredictWind, SailFlow and Windy. Plus, I check The Weather Channel, Weather Underground (formerly Intellicast) and the National Weather Service. Often, there are subtle variations in forecasts. When there is a discrepancy, I use my best judgment based on my own experience of a location, or I try to understand the different trends.

Newspapers publish weather information that offers a good start for a day’s forecast. The National Weather Service broadcasts continuous updates on VHF radio. I smile when I think about the many hours I’ve spent sitting below at a chart table listening to weather briefings delivered by a computerized, monotone voice. I like to write down the information and compare the weather trends over several hours, with a mobile phone providing access to updated information.

In addition to all these helpful modern tools, I also listen to the old salts who hang around the waterfront and offer weather folklore. I am amazed how veteran sailors can accurately predict the weather based on decades of experience.

For example, thick morning dew on grass indicates that a strong thermal sea breeze can be expected. Or the nifty adage, “Red sky at morning, sailors take warning; red sky at night, sailor’s delight.”

Observing cloud configurations gives a clue about weather changes. Land heats up during daylight hours, and clouds will build as moisture accumulates well above the surface. During the summer months, giant cumulonimbus, anvil-shaped thunderheads indicate that squalls are developing. Sailors should take the warning seriously and prepare for intense rain and strong wind.

I have seen waterspouts form under cumulonimbus clouds. My greatest fear during thunderstorms is lightning strikes, but most of the time, storms do not last long and will bring relief from hot weather.

Cirrus clouds are high, white delicate filaments made up of ice crystals that give sailors long-range forecasts. These clouds appear ahead of approaching fronts. Wispy clouds pose little threat, but dense patches of cirrus clouds indicate rainy weather in the area.

Contrails in the wake of high-flying aircraft show the state of the upper atmosphere. When contrails are slow to disappear, it means a weather front could be approaching. Stratus clouds are relatively low and often create light rain, but not much wind.

During periods of very light wind, I head in the direction of cloud masses. Usually, wind can be found under clouds.

A word of caution to include an alternative system for monitoring the weather. If the engine or batteries were to go out, then a handheld VHF radio and GPS will be essential pieces of equipment to track weather and position. A compass, depth sounder and masthead wind indicator are vital on any sailboat.

Fog can hinder a day on the water. GPS and radar are useful tools when sailing in thick fog.  Still, it is imperative to keep a diligent lookout, and most important, listen for sounds on the water like motors, bells on buoys, foghorns and voices. Take bearings on your surroundings to understand if you need to steer clear of obstructions or other vessels. In times of uncertainly, use your VHF radio to communicate with nearby vessels about your course, speed and position.

The Beaufort Wind Scale was created in the early 1800s by a royal naval officer, Sir Francis Beaufort. The scale ranges from Force Zero (no wind) to Force 12 (hurricane-strength winds over 64 knots). Images of the waves in winds of Force Nine and higher are frightening—and a good warning for sailors if this is the forecast.

As wind strength builds, intense wave action and height will follow quickly. If the tidal current is flowing in the opposite direction of the wind, then the waves will be short and choppy. A copy of the annual tide and current tables should be included in every chart table.

Keeping track of water depth is also important. As a rule, I like to have at least 4 feet of water below my keel. Running aground is an annoyance in waters with sandy or muddy bottoms, and it’s far more serious on a rocky coast.

The U.S. Coast Guard plans to reduce the number of channel markers on the waters of the East Coast and New England. Hazards to navigation are many in areas with large tidal ranges. Weather events can cause havoc in shoaly areas because of choppy waves and hidden rocks. Be particularly diligent when the seas are rough during storms.

Cold fronts and squall lines are dangerous weather events. Winds can suddenly change direction and build within seconds. If a front is approaching, then prepare the crew to reef or roll up the sails before the weather arrives. During the initial blast, the color of the sky and water will darken, and the environment will be disorienting. With thunder and strong wind, it is difficult to hear commands. Heavy rainfall adds to the confusion on deck.

One of the great joys in sailing is when a thermal breeze arrives after period of no wind. As the land heats up, the hot air rises, creating cumulus clouds. Eventually, a cool breeze from the water fills in, creating a sea breeze. The moment of the new wind’s arrival is always a happy moment.

In fact, all kinds of weather can make for memorable experiences. On one bright afternoon on the Chesapeake Bay, I saw some intense clouds building over land. We were sailing about 4 miles from land, and it was going to be difficult to return to Annapolis harbor before the storm.

The squall was approaching fast. We had a few youngsters on board who were not sure whether they should be excited or horrified. I worked to stay calm, with the hope that the kids would be calm too.

We could see lightning bouncing off the water only 1 mile away. I headed for the lee side of an anchored ship, took the sails down and waited for the storm to pass. I kept the boat about one length from the ship. The crew waved from the bridge. I figured the lightning would strike the higher deck of the ship before hitting my mast.

About 20 minutes later, the sky cleared, a new breeze filled in from the south, and we continued our sail. The young people talked about the squall for the rest of the weekend. 

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