Our WRF modeling study supports the hypothesis that higher than usual for early September Sea Surface Temperatures (SSTs) in GC significantly enhanced the intensity of Norbert and influenced the rainfall rates and the intensity of the flash flood. In particular, the onset of the heavy rainfall occurs after the SSTs exceeded 29oC. Here we explore this idea in a modeling context using the WRF to simulate the 2014 Arizona flood. To test this hypothesis, we investigate boundary layer and the atmospheric circulation in Arizona before and during the heavy rain events. Both the boundary layer water content and CAPE over Maricopa County, and the atmospheric circulation over Arizona changed dramatically over the course of the numerical simulations. WRF ARW (Advanced Research WRF model) successfully simulated the boundary layer properties and CAPE during the flood. The simulated Norbert moisture movement triggers strong winds, damaging rain, and thunderstorms for several days across Arizona. These are serious life and aviation hazards.
After analyzing the predicted evolution of the monsoonal boundary layer properties, and the impact of Hurricane Norbert in numerous WRF simulations, a new understanding emerges as to how the lower atmosphere over the GC interacts with the remnants of hurricane moisture to enhance dramatically the monsoon rainfall. A boundary layer parameterization having high vertical resolution with an accurate treatment of physical processes appears essential for capturing accurately the flood event.