hPa

hPa, or hectopascal, is the standard unit used on marine weather charts and forecasts to express atmospheric pressure; 1 hPa equals 1 millibar. For boaters, it describes the weight of air over the sea surface and helps identify highs, lows, ridges and troughs that drive wind and weather.

Monitoring hPa trends is often more useful than a single reading. A rapid fall can warn of an approaching low, front, stronger wind or deteriorating sea state, while a steady rise often suggests more settled conditions. Pressure changes should be read alongside Wind Speed, Wind Direction and Sea State when choosing a route, reefing plan or anchorage.

PredictWind displays pressure fields in forecasts and GRIB data so you can compare models such as ECMWF, GFS and ICON, spot pressure gradients, and plan around developing systems. In Weather Routing and Departure Planning, hPa patterns help explain why the recommended route avoids certain lows or targets a more favourable window.