Millibar

A millibar (mb) is a unit of atmospheric pressure used on marine weather charts and forecasts. At sea, it describes the weight of the air above the ocean surface, usually plotted as sea-level pressure to show highs, lows, ridges, and troughs that drive wind and weather.

For boaters, millibar trends are often more useful than a single reading. A rapid fall can signal an approaching low, stronger Wind Speed, rain, and deteriorating Sea State; a steady rise usually indicates improving conditions. Monitoring Pressure helps with reefing decisions, departure timing, anchorage choice, and offshore watchkeeping.

Millibars are closely related to hPa and are numerically identical, so 1013 mb equals 1013 hPa. PredictWind forecasts, GRIB downloads, weather maps, Weather Routing, and Departure Planning use pressure fields from leading models to help identify safe windows and avoid developing systems.