Rapid intensification (RI) is any process wherein a tropical cyclone strengthens very dramatically in a short period of time. Tropical cyclone forecasting agencies utilize differing thresholds for designating rapid intensification events, though the most widely used definition stipulates an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots in a 24-hour period. However, periods of rapid intensification often last longer than a day. About 20–30% of all tropical cyclones undergo rapid intensification, including a majority of tropical cyclones with peak wind speeds exceeding 51 m/s.