Abstract
Tropical Cyclone (TC) RAI (2021) made a devastating landfall in the Siargao-Dinagat Islands of the southeastern Philippines on December 16, 2021, causing about USD 1.05B in damage, 405 reported dead and 52 missing. This TC reached a maximum sustained wind speed (MSW) of 105 kts (194.5 kph) and 915 hPa mean sea level pressure (MSLP) according to the WMO-IBTrACS. When compared with Philippine landfalling TCs from 1979 to 2020, this TC, among super typhoons (STYs), ranked second in terms of MSW and translational speed. Moreover, the TC had an unusual westward movement, faster translational speed, larger radius, and greater intensity when compared to seven other TCs that made landfall in the same month and region. The environmental factors along the path of TC RAI that may have contributed to its intensification include, but are not limited to, the above normal SST (+ 0.5 to 1.5°C) and ocean heat content, high low-level relative humidity (RH), and high specific humidity. These factors resulted in strong convergence and intensification until landfall. Composite analysis of and comparison with the seven TCs reveal that the atmospheric conditions during TC RAI had a consistently higher near-surface RH850hPa − 500hPa, which helped sustain its movement across the central Philippines. Moisture from the Philippine Sea was also drawn into central Philippines, which received at least 125–150 mm of rainfall. The extension of the western North Pacific Subtropical High along 20°N and strong easterly flow may have facilitated the TC’s unusual straight and westward movement.