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Numerical experiments are carried out to explore the impacts of local and remote forcing on the interannual variability of tropical cyclone (TC) frequency. The first two groups of experiments focus on the regional simulations of Atlantic TCs, and the lateral boundary conditions and sea surface temperature (SST) are specified to investigate the relative importance of remote and local forcing. The results suggest that remote processes outside the North Atlantic, particularly extratropical processes, play an important role in modulating Atlantic TC frequency and that the remote impacts may exceed the impacts of local SST in some years. The total TC frequency in the northern tropics is explored in the third group of experiments. In contrast to the North Atlantic, tropical SST plays a dominant role in modulating the total TC frequency in the northern tropics. The difference may help to explain the uncertainties in the projections of future Atlantic TC frequency.

Plain Language Summary Skillful seasonal prediction of tropical cyclones (TCs) can help storm preparedness and mitigate their destructive impacts and is thus of profound socio-economic value. TC activity on the seasonal time scale is subject to local forcing associated with variability in tropical sea surface temperature (SST) and remote extratropical influence. Numerical model experiments are carried out to explore the impacts of local and remote forcing on the interannual variability of TC frequency. The experiments suggest that the remote forcing, in particular, extratropical processes, plays an important role in modulating Atlantic TC frequency and tropospheric variability and that the influence may even exceed that of local SST in some years. In contrast to the Atlantic basin, tropical SST plays a dominant role in modulating the total TC frequency over the northern tropics. The sensitivity of Atlantic TCs to extratropical processes may help explain the uncertainties in the projections of future Atlantic TC frequency.