The weather plays a crucial role for all sailors, whether yachtsmen or professionals. Predicting weather conditions at sea requires a good understanding of atmospheric phenomena and the tools available to us. In this article, we explore the essential concepts related to marine weather, while deciphering the essential technical terms.
Barometric pressure and its role in the weather
Barometric pressure is one of the key elements for analyzing weather conditions. It corresponds to the force exerted by the atmosphere on a given surface, measured in hectopascals (hPa) or millibars (mb). Standard pressure at sea level is 1013 hPa.
Pressure variations can be used to locate areas of low pressure (often associated with bad weather) or high pressure (synonymous with calm, sunny weather). These pressure changes are represented by isobars, lines on a weather map linking points of similar atmospheric pressure.
Pass, barometric swamp, talweg and ridge: concepts you need to know
When studying weather maps, several specific terms are often used:
- Collar this zone lies between two lows. Relatively calm, it is characterized by light and variable winds.
- Barometric swamp a region where isobars are widely spaced and disorganized. Here, winds are light, weather is often unstable, and average pressure is around 1013 hPa.
- Talweg a low-pressure protrusion in the shape of a "V" on the isobars. It's a zone of inward pressure decrease, often associated with shifting winds and cold fronts.
- Back the opposite of a trough, this outgrowth of a high-pressure system resembles an inverted "U". Pressure rises inwards, and the weather is generally fine and stable.
Meteorological tools: barometer, anemometer and thermometer
To observe and analyze these phenomena, several instruments are essential:
- Barometer atmospheric pressure gauges are used to measure atmospheric pressure. The most accurate models are mercury-based, but modern electronic versions are also used.
- Anemometer this device measures wind speed, expressed in metres per second (m/s) or knots.
- Thermometer : Used to measure air temperature, it is essential for completing weather surveys.
Buys-Ballot's law and winds
Buys-Ballot's law helps to determine areas of high and low pressure according to wind direction. In the Northern Hemisphere, if you're facing into the wind, low pressure will be at the back of your right hand, while high pressure will be at the front of your left.
Why is this essential for browsers?
To sail safely, it is crucial to know how to interpret weather charts and associated phenomena:
- Forecasting weather fronts: Identifying a trough or ridge of high pressure allows you to anticipate conditions at sea.
- Adapt your sailing: In the event of a low-pressure system or barometric swamp, it is often preferable to delay your departure.
- Read local weather trends: The barometer is a valuable ally for monitoring pressure variations and adjusting your itinerary.
In a nutshell
Understanding marine weather gives you the means to sail serenely and adapt to conditions at sea. Mastering concepts such as passes, talwegs and barometric marshes, and using tools such as barometers and anemometers, are essential for safe navigation.
To deepen your knowledge, don't hesitate to consult specialized training courses or explore online teaching resources. You'll soon know all there is to know about the weather!
