Shear lines trigger heavy rainfalls in the Philippines during the winter monsoon

Heavy rainfall events (HREs) occur almost throughout the year in the Philippines, with relatively limited research during the winter monsoon. This study analyzes the 20-year (2003–2022) daily precipitation from 55 rain gauges and Integrated Multi-satellitE Retrievals for GPM (IMERG) from November to February. HREs are classified into three clusters by employing a cluster analysis on the most pertinent principal modes extracted from the principal component analysis. Each cluster exhibits a distinct heavy rainfall spatial pattern, mostly showing more than 50 mm/day of rainfall in the eastern part of the country. We noted that heavy rainfall in the Philippines during the winter monsoon occurs during a strong East Asian Winter Monsoon and caused by the interaction of shear line and low-level cyclonic vortex. The different location of rainfall maxima in each HRE cluster is a result of the variation of locations of the shear line and cyclonic vortex.