Abstract
Extreme Rapid Intensification (ERI) of a tropical cyclone is defined here as a 60+ knot increase in the maximum surface winds over a 24-hour period, or double the intensification rate of the typical definition of rapid intensification (RI). This work examines ERI events to determine if there are any observable indicators that an ERI event is commencing in a tropical cyclone. Over 41 years, extending from 1980 to 2020, a general geographical climatology was developed for ERI episodes in the North American basins. ERI episodes occur most frequently in the Eastern Pacific warm pool and the Western Caribbean. To identify how the convective structure of a tropical cyclone evolved during the onset of ERI, the brightness temperature along the radius of maximum wind was analyzed in polar coordinates during a 12-hour period around when ERI commenced. Three recent ERI cases were chosen for this analysis due to their reliable radius of maximum wind estimates from frequent in situ observations by Air Force and NOAA reconnaissance aircraft: Hurricane Matthew (2016), Hurricane Maria (2017), and Hurricane Delta (2020). Our analysis of these cases reveals that their ERI events were commenced by an intense convective burst during the afternoon that rapidly axisymmetrized about the center of circulation. Storms that underwent ERI in the Eastern Pacific and Atlantic basins had their ERI episodes commenced by convective bursts that initiated most frequently during the afternoon hours, between 12 pm and 6 pm local time. Furthermore, a contraction of the radius of maximum winds preceded the onset of ERI in the three cases analyzed, with a similar trend being noted in ERI cases occurring in the Atlantic from 1992 to 2020.