Spatial variations in the seasonal cycle of sea surface temperature (SST) are studied over the western North Pacific using a high-resolution climatology. In addition to monsoon, bathymetry and tidal mixing, western boundary currents and their extensions/branches are found to have a significant effect on the annual range of SST, with reduced values on the paths of warm currents and increased ones on the paths of cold currents. This is due to the asymmetric effect of ocean currents on SST in time: small in summer but large in winter when both the deepened mixed layer and increased SST gradients enhance the relative importance of ocean thermal advection to balance the heat flux to the atmosphere. Along with recent studies of decadal variability, our results reaffirm the role of ocean dynamics in climate.