Importance of short interval (six hour) intensity changes in understanding the rapid intensification/weakening trends of tropical cyclones

The intensity of tropical cyclones (TCs) varies at different rates throughout their life cycle. Among them, rapid intensification (RI, intensity change ≥ 30 knots/24 hr) and rapid weakening (RW, intensity change ≤ -30 knots/24 hr) of TCs are extremely difficult to predict. Despite numerous studies, the RI and RW of TC continue to cause forecasting errors. Considering the increasing frequency of RI/RW cases, studying the variations of short-period (6-hour) intensity changes occurring within RI/RW events can help us better understand RI/RW events. We used the IBTrACS global TC dataset (1981–2020) to study how variations in 6-hour intensity changes relate to trends in RI&RW events. Generally, the 24-hour RI (RW) events are built upon 6-hour intensity changes with a magnitude of 10 kt (-10 kt). In the last two decades, this magnitude has increased to 15 kt (-15 kt) and, in rarer events, up to 55 kt in 6-hours. This increase explains the rise in stronger RI/RW events. Importantly, even non-RI and non-RW events now more frequently exhibit 6-hour intensity changes of magnitude ±10 kt, thereby increasing the likelihood of TCs transitioning into RI/RW phases. As a result, the upward trends in RI and RW events measured over a 24-hour period are largely explained by the amplification of the upward trends in 6-hour intensity changes with increasing measuring interval. It is found that even minor TCs (cyclones which do not reach higher intensities during their lifetime) are also growing at an increased intensification rate at 6-hour interval, which was not observed/reported at 24-hour intensity changes. This has led to a decrease in the average duration of the intensification phase, which has decreased at a rate of 0.67-hour per year between 1981 to 2020. These findings can help forecasters identify early signs of rapid intensity changes, enabling more timely and accurate warnings in a changing climate.