Isobars are lines on a weather map connecting points of equal atmospheric pressure, typically measured in millibars (mb). They are essential for sailors to predict wind speed and direction: closely spaced lines indicate steep pressure gradients, strong winds, and unstable weather, while widely spaced lines suggest light, calm conditions.

Key Sailing Insights from Isobars
Wind Strength: The closer the isobars, the stronger the wind. Far apart means light winds.

Wind Direction: Wind tends to blow almost parallel to isobars, circulating clockwise around Highs and counter-clockwise around Lows in the Northern Hemisphere.

High-Pressure Areas: Resemble mountain systems with clear, stable weather.

Low-Pressure Areas: Resemble valleys, often bringing clouds and stormy weather.