Variability of Tropical Cyclone Rapid Weakening on a Global Scale

Rapid intensity changes of tropical cyclones (TCs) are known to negatively impact intensity forecasts, an issue that has slowed improvements in the 24-48 h forecast time frame. While many studies have focused on improving the identification and predictability of rapid intensification events (a 30-kt [15.4 m s^-1] increase in 1-minute sustained winds in 24 h), less work has been done on rapid weakening (RW), defined as a minimum 30-kt decrease in 1-minute sustained winds in 24 h while the TC is over open ocean.

This research expands on previous work by evaluating RW events in all tropical basins. RW is defined from National Hurricane Center and Joint Typhoon Warning Center best tracks due to their 1-minute sustained wind speed measure of intensity. To focus on over-water weakening, only 24-h periods during which the TC center remained at least 250 km from land are included. The frequency of over-water RW is much greater in the eastern North Pacific (ENP) and western South Pacific (WSP) compared to the North Atlantic (NAL) due to both more land and a larger extent of conducive SSTs in the NAL. ERA-Interim reanalysis data show consistent dry air intrusions during RW, with stronger decreases in mid-level humidity occurring in the ENP and WSP compared to the NAL and western North Pacific. The potential application of these and other fields to intensity prediction is explored, and future work will investigate near-coastal (< 250 km) RW events due to the impacts of these rapid intensity changes on hazard preparation.