Rapid intensification

Rapid intensification (RI) is any process wherein a tropical cyclone strengthens 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 (55 km/h; 35 mph) 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 (180 km/h; 110 mph).

Rapid intensification constitutes a major source of error for tropical cyclone forecasting, and its predictability is commonly cited as a key area for improvement. The specific physical mechanisms that underlie rapid intensification and the environmental conditions necessary to support rapid intensification are unclear due to the complex interactions between the environment surrounding tropical cyclones and internal processes within the storms. Rapid intensification events are typically associated with warm sea surface temperatures and the availability of moist and potentially unstable air. The effect of wind shear on tropical cyclones is highly variable and can both enable or prevent rapid intensification. Rapid intensification events are also linked to the appearance of hot towers and bursts of strong convection within the core region of tropical cyclones, but it is not known whether such convective bursts are a cause or a byproduct of rapid intensification.

The frequency of rapid intensification has increased over the last four decades globally, both over open waters and near coastlines. The increased likelihood of rapid intensification has been linked with an increased tendency for tropical cyclone environments to enable intensification as a result of climate change. These changes may arise from warming ocean waters and the influence on climate change on the thermodynamic characteristics of the troposphere.