Impacts of ENSO on Philippine Tropical Cyclone Activity

This study investigates the El Nino-Southern Oscillation (ENSO) contribution to Philippine tropical cyclone (TC) variability, for a range of quarterly TC metrics. Philippine TC activity is found to depend on both ENSO quarter and phase. TC counts during El Nino phases differ significantly from neutral phases in all quarters, whereas neutral and La Nina phases differ only in January-March and July-September. Differences in landfalls between neutral and El Nino phases are significant in January-March and October-December and in January-March for neutral and La Nina phases. El Nino and La Nina landfalls are significantly different in April-June and October-December. Philippine neutral and El Nino TC genesis cover broader longitude-latitude ranges with similar long tracks, originating farther east in the western North Pacific. In El Nino phases, the mean eastward displacement of genesis locations and more recurving TCs reduce Philippine TC frequencies. Proximity of La Nina TC genesis to the Philippines and straight-moving tracks in April-June and October-December increase TC frequencies and landfalls. Neutral and El Nino accumulated cyclone energy (ACE) values are above average, except in April-June of El Nino phases. Above-average quarterly ACE in neutral years is due to increased TC frequencies, days, and intensities, whereas above-average El Nino ACE in July-September is due to increased TC days and intensities. Below-average La Nina ACE results from fewer TCs and shorter life cycles. Longer TC durations produce slightly above-average TC days in July-September El Nino phases. Fewer TCs than neutral years, as well as shorter TC durations, imply less TC days in La Nina phases. However, above-average TC days occur in October-December as a result of higher TC frequencies.