Rainfall Rate

A measure of rainfall intensity calculating the amount of rain that would fall over a given time interval. Rainfall can be categorized as light (< 2.5 mm/h), medium (2.5-7.6 mm/h), heavy (> 7.6 mm/h), or violent (> 50 mm/h).

Trade winds carry moist ocean air from the northwest, bringing moderate showers on windward coasts that increase in intensity, frequency, and persistence as they climb mountain slopes. Leeward (westward) areas receive occasional light trade-wind showers that may drift over from the mountains. Storm episodes usually occur when the trade winds have died down, making winter the rainy season. Mount Waiʻaleʻale on the island of Kauaʻi averages more than 460 inches (11.7 m) of rain per year with a planet-wide record of 683 inches (17.3 m) in 1982. In contrast, the rest of the state averages 70 inches (1.8 m) per year and the ocean surrounding Hawaiʻi averages only 25 inches (0.6 m).