A Tale of Seven Hurricanes and Their Interaction with the Monsoon: A Modeling Study

The goal of this study is to analyze how hurricanes Lane (2000), Juliette (2001), Marty (2003), Javier (2004), Henriette (2007), Odile (2014), and Norbert (2014) in the Eastern Pacific affected the monsoon season and to model the resulting devastating flash floods in Arizona during the enhanced monsoon events of 2014. The Phoenix flash flood of September 7-8th, 2014 resulting from the hurricane Norbert, and the floods associated with hurricane Odile are investigated in this Weather Research and Forecasting (WRF) modeling study. Our goal is to simulate the general features of the boundary layer in Arizona prior to and during the flash flood events and to study the related hazardous weather patterns.

Warmer than normal sea surface temperatures helped to maintain the intensity of the storms. The rainfall total during the 7-8 hours of Chandler, AZ flood was greater than the total precipitation during the months of June, July, and August 2014 (NWS 2014). According to NOAA, this was a once in 200 year period event. Our WRF modeling study supports the hypothesis that higher than usual for early September SSTs significantly enhanced the intensity of Norbert and Odile, and influenced the rainfall rates and the intensity of the flash floods. 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.

Most of the damage caused by Odile was sustained in Mexico as it moved up through the very warm waters of Baja California. As Odile approached The United States on September 16th, it is important to note Hurricane Norbert’s devastation just 8 days earlier, which already caused record-breaking rainfall totals. Arizona experienced heavy flooding from September 17th –20th, with Sierra Vista, Bisbee, and the Douglas areas each collecting over 3.00 inches of rain.

The extent to which the precipitation, atmospheric circulation patterns, and Gulf of California (GOC) surge events are influenced by the monsoon is also considered. We show that the relationship between surge strength and monsoonal precipitation in Arizona and New Mexico is not simple or linear.

Results indicate that a significant fraction of the monsoonal flash flood events in 2014 are related to hurricanes Norbert and Odile. The North American Monsoon in 2014 was enhanced by the presence of tropical storms and hurricanes in the northeast Pacific ocean.