Relative contributions of environmental factors on different time scales to tropical cyclogenesis over the eastern North Pacific

Abstract The present study investigates relative contributions of large‐scale environmental factors on interannual, intraseasonal, and synoptic time scales to tropical cyclone (TC) genesis over the eastern North Pacific (ENP) during TC seasons of 1979–2013 from the perspective of TC genesis time and position. Conditional sorting displays that the synoptic component is more important in the contribution of lower‐level vorticity and mid‐level specific humidity to TC genesis compared to interannual and intraseasonal components. The convection contributes to TC genesis mainly through synoptic and intraseasonal components. Synoptic‐scale tropical disturbances mainly obtain barotropic eddy energy from climatological mean flows. TCs appear most frequently when vertical wind shear anomalies are between 0 and 3 m s−1, in which interannual and intraseasonal westerly wind anomalies make a positive contribution due to climatological easterly wind shear. When total SST exceeds 28°C, the interannual component of sea surface temperature (SST) is positive, and then it has a positive contribution to TC genesis. In addition, there are notable differences of relative contributions of different time scale components of large‐scale factors among the ENP, northern Atlantic Ocean, and western North Pacific.