The Record‐Breaking 2015 Hurricane Season in the Eastern North Pacific: An Analysis of Environmental Conditions

Abstract

The presence of a near‐record El Niño and a positive Pacific Meridional Mode provided an extraordinarily warm background state that fueled the 2015 eastern North Pacific hurricane season to near‐record levels. We find that the western portion of the eastern North Pacific, referred to as the Western Development Region (WDR; 10°–20°N, 116°W–180°), set records for named storms, hurricane days, and Accumulated Cyclone Energy in 2015. When analyzing large‐scale environmental conditions, we show that record warm sea surface temperatures, high midlevel relative humidity, high low‐level relative vorticity, and record low vertical wind shear were among the environmental forcing factors contributing to the observed tropical cyclone activity. We assess how intraseasonal atmospheric variability may have contributed to active and inactive periods observed during the 2015 hurricane season. We document that, historically, active seasons are associated with May–June El Niño conditions, potentially allowing for predictability of future active WDR seasons