Waves, Wind, And Wisdom: A Sailor's Guide To Weather Forecasting

Choosing when to set sail and when to stay put is a crucial part of having an enjoyable time out on the water. And with a slew of modern weather devices, apps, and state-of-the-art weather forecasts, you might assume that surprises at sea are a thing of the past.


However, the reality is that even the most sophisticated technology has its limitations. No matter how technologically advanced and up-to-date weather forecasts and all your wind and wave apps are, there are instances of localized weather systems that are just not shown or caught on any weather prediction devices, or when those pesky technological gremlins strike and leave your apps and radar systems useless. No matter what the case for being left in the dark with the weather, there are always ways to determine your immediate weather.


Complementing your weather prediction technology with fundamental weather-reading skills will help to give you a holistic view of your local weather. Here is a look at some fundamental weather wisdom that every sailor worth their salt should know.


Under Pressure 

One of the oldest- and still one of the most reliable- indicators of imminent weather changes is barometric pressure: A falling barometer signals approaching storms, while a rising one hints at fair weather ahead.


Generally, pleasant weather will always be in an area with high pressure, and stormy weather will be in an area with low pressure. Air always wants to go from a high-pressure area to a low-pressure area, and because of this, areas that sit between high and low-pressure regions are often very windy. The faster this change happens, the more winds will likely accompany the change.


Combining the barometer's readings with visual cues, such as dark clouds and increasing wind, provides a comprehensive understanding of the immediate weather outlook. If falling barometric pressure is accompanied by the sighting of dark clouds or an increase in wind, you know that you should start dropping the sails and grabbing a rain jacket.


In a world dominated by apps and gadgets, you might ask yourself why you would still want such a low-tech device invented almost 400 years ago. Well, for precisely that reason, its low-tech simplicity and reliability make it a timeless tool for predicting imminent weather changes- it will not be impacted by internet outages, water damage, not being charged or updates not installed, or payments not being received – you hang it on a bulkhead and forget about it.


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Reading The Skies 

All the fundamentals of what to expect from your localized weather can be found by looking to the skies. The shape of a cloud, its speed, and its position in the sky are all hints of what the weather will be doing soon.


For instance, cumulus clouds signify fair weather, while towering cumulonimbus clouds warn of storms. Familiarize yourself with the ten main cloud types, such as cirrus, cirrocumulus, and cirrostratus, as each type provides valuable insights into atmospheric conditions, helping you anticipate local weather fronts.


Clouds rarely tell the whole story on their own. Combine cloud observations with other indicators such as wind direction, barometric pressure, and sea state to comprehensively understand local weather. Different regions will also have their own unique cloud behaviors. Engage with local sailors, listen to their stories, and learn from their experiences about how clouds predict weather patterns in those specific areas.


We highly recommend investing in a book or app tailored to understanding different cloud types, like the Centre for Science Education's 'Field Guide To Clouds.' 


Halos and Coronas

Celestial objects like the sun, moon, and stars can highlight moisture in the air that the naked eye cannot see. This feature makes them excellent weather predictors. An old rhyme says: "Ring around the moon, rain before noon. Ring around the sun; rain before the day is done."


When you see a halo around the sun, that indicates moisture is high in the atmosphere. If the halo is followed by high, thin, wispy cirrus clouds, a storm system is approaching you - typically 24 to 48 hours away.


Whether the air is cloudy, hazy, or clear, these rings reflect moisture-laden ice crystals in the atmosphere. Large rings are called haloes, and small ones are called lunar or solar coronas. The tighter the ring is to the edge of the celestial body, the more time you have before a rainstorm. Large, loose rings are more predictive of rain within a few hours or less. The ring's strength is often correlated to the strength of the coming rain.


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Wind Patterns

Always be aware of the prevalent wind directions in your sailing region. A shift in direction means a change in weather. Most prevailing winds in the Northern Hemisphere go from west to east. A persistent wind blowing due north or south may have a robust system connected to it, and it may be worth listening to the VHF for a forecast or checking your weather radar for approaching weather.


Remember that winds can mean either an approach of good or bad weather, so watch for other signs to determine the direction that it is likely headed. This includes the changes in cloud types and barometric pressure.


Localized changing wind patterns and their meaning can also be interpreted correctly by listening to local knowledge.


Local Knowledge And Lore

Indigenous knowledge of weather patterns is invaluable for navigating specific waters and ensuring you're well-prepared for any surprises, as different regions can have other localized weather systems and typical weather patterns at sea.


If you have ever sailed in the Mediterranean, you will be aware of Katabatic winds that can wreak havoc on your plans as nightfall approaches the western Mediterranean or the intense and unpredictable Bora winds in Croatia.


Accessing local lore becomes particularly crucial when navigating unfamiliar waters. Take a walk around the marina and ask the local fishermen, or buy a couple of drinks at the local bar to pick up some local advice on what to watch out for weather-wise.


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Modern Technology at Your Fingertips

Apps like Windy, Predict Wind, or NOAA Weather provide up-to-date forecasts, satellite imagery, and real-time weather data. It lets you see approaching precipitation, lightning, isobars (lines of barometric pressure), wave heights, sea surface temperatures, etc. All perfectly laid out on your chart plotter.


It is one thing to look at some bad weather coming across the sea. It is another to see the severe weather and be able to go around it or through it. When used with your own visual interpretation of the weather, this technology enhances decision-making and allows for strategic navigation.


Remember that you should never mindlessly rely on just one source of weather information; always use your line of sight, local knowledge, weather apps, wind speed, cloud formations, and any other sources available to you to get a comprehensive insight into maritime weather systems.


Tradition And Technology

From understanding the nuances of cloud formations to harnessing the power of modern forecasting tools, the ability to foresee weather patterns is a skill that transforms uncertainty into a navigational advantage. By combining traditional forecasting techniques with modern technology and state-of-the-art features onboard, you're well on your way to confidently navigating the seas regardless of the weather.


Fair winds and smooth sailing!

Hanrie Bosch