NWC REU 1998



Relationship Between Easterly Waves and Surges Over the Gulf of California During the Mexican Monsoon

Ryan D. Fuller and David Stensrud



Steady increasing concerns have prompted need for improved weather forecasting over the Southwest United States in recent years. With factors including increasing population and economic demands, monsoonal climates affect more people than ever before. In just three months, the main convective weather system of the region, the Mexican Monsoon, produces approximately 30-50% of all rainfall over the southwestern United States and as much as 70% over Mexico. In past years, forecasters have found difficulties predicting surge events that lead to the formations of heavy rains and severe weather outbreaks caused by the monsoonal conditions. The use of Mesoscale models (e.g.Eta) display the lowest accuracy over this region and too few surface observation mount to the difficulties.

In past studies, it was believed that the Gulf of Mexico and the Caribbean were the sources of moisture leading to the monsoon, see Jurwitz (1953). In the1970's Hales (1972), concluded that the Gulf of California was the likely source, but could not explain the mechanisms involved. The Stensrud et al. (1997) study showed that there is a relationship between easterly waves leading to surges found propagating north from the Gulf of California on at least one event. This most current study examined a 13 year period to see if that relationship is sound. Relationships among three features are examined over southwest Arizona. Those include surge passages over Yuma, 850 hPa meridional wind speed, and 200 hPa meridional wind speed.. With high accuracy, results conclude that approximately 2 days after easterly waves occur drastic changes occur signaling surge events. Without easterly waves, significant surge events did not occur with high frequency.

Paper available upon request.