Tropical cyclone climatology and variability in Taiwan and Philippine Region during 1979-2018

Taiwan and Philippine (TWPH) (117 129 degrees E, 5 26 degrees N) is a region with most frequent and intense tropical cyclone (TC) influence in the world. This paper documents the climatology and variability of TWPH TC activity with specific attention to the difference in the TCs formed over the western North Pacific (WNP) and over the South China Sea (SCS). The spatial characteristics of TWPH TCs are analyzed based on the accumulated cyclone kinetic energy (ACE) in four sub-areas where distinctly different TC seasonality and variability is found. Different from over the broad Northwest Pacific Basin (0 60 degrees N, 100 degrees E 180 degrees) where the WNP-born TC frequency dropped sharply in late-1990s and the SCS-born TC frequency slightly increased in mid-1990s, over TWPH three distinct epochs are identified. A weak variability epoch occurred during 1979 1996, a persistent low-ACE epoch during 1997 2002, and a more variable epoch during 2003 2018. The second epoch is most noteworthy. The unusually weak TC activity during this period in particular over the Philippines was associated with anomalously strong anticyclone over the SCS and the Philippine Sea during the East Asian summer monsoon season. The strong anticyclonic circulation appeared as a descending leg of the enhanced East Asian summer monsoon during summer (July to September). During autumn and early winter (September to December) the Philippine Sea anticyclone was interpreted as the descending Rossby wave response to the suppressed convection over tropical western Pacific. The anomalous anticyclone strengthened the low-level confluent flow and convection over the SCS. The findings are useful to real-time TWPH TC activity monitoring and analysis.