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While some studies related the enhanced tropical cyclone (TC) formation to the ongoing global warming,some studies attributed it to the warm phase of the Atlantic multidecadal oscillation (AMO).The study identifies the influences of the Atlantic multidecadal oscillation (AMO) and global warming on TC formation in the North Atlantic basin,respectively.Two leading patterns are identified in the climate change of TC formation on time scales longer than interannual.The first pattern is associated with AMO and its spatial pattern shows the basin-scale enhancement of TC formation during the AMO positive phase.The second pattern is associated with global warming,showing enhanced TC formation in the east tropical Atlantic (5°-20°N,15°-40°W) and reduced TC formation from the southeast coast of the United States extending southward to the Caribbean Sea.In the warm AMO phase,the basin-wide decrease in vertical wind shear and increases in mid-level relative humidity and maximum potential intensity (MPI) favor the basin-wide enhancement of TC formation.Global warming suppresses TC formation from the southeast coast of the United States extending 2 southward to the Caribbean Sea through enhancing vertical wind shear and reducing mid-level relative humidity and MPI.The enhanced TC formation in the east tropical Atlantic is due mainly to local increase in MPI or sea surface temperature (SST),leading to a close relationship between the Atlantic SST and TC activity over the past decades.