Off northeastern Taiwan, enhancement of sea surface chlorophyll‐a (Chl‐a) concentration is frequently found after typhoon passages. From 1998 to 2013, 46 typhoon events are analyzed to examine the variations in Chl‐a concentration from satellite ocean color data. On average, Chl‐a concentration increased by 38% after a typhoon passage. Noticeably, four remarkable Chl‐a increases after typhoons coincide with pre‐existing oceanic cyclones in the study area. The Chl‐a increase is significantly anticorrelated (p < 0.01) with relative SSH, defined as the difference of SSH in the study area and in the surrounding area. To assess the impact of pre‐existing cyclones on the upper ocean response to typhoons, we conduct a series of numerical experiments to simulate the oceanic response to Typhoon Kaemi (2006) with or without a pre‐existing oceanic cyclone, and with or without strong typhoon winds. The results show that the experiment with a pre‐existing oceanic cyclone produces the largest upwelling due to cyclone intensification, mainly induced by the positive wind stress curl dipole northeast of Taiwan.

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