Some mechanism, perhaps a coastal current or solar heating, causes the warmest water to migrate up the coast, beginning in late May or June. As the tongue of warm water moves up the coast at a rate of 800 miles a month, it appears to steer the prevailing winds southwest to southeast. In July, the winds are aligned with sea surface temperature gradients, picking up the maximum amount of moisture from the warmest water, and blowing parallel to the coast up the Gulf of California. Surface winds and low pressure may draw the moisture-laden air inland, where it explodes in thunderstorms over the deserts of northern Mexico and the U.S. Southwest. From this picture, they theorize the temperature and strength of the coastal current may regulate atmospheric processes, which in turn may determine the strength of the monsoon season.
Wind blowing over warmer water picks up more moisture, contributing to stronger thunderstorms.
Mitchell and Brown's theory about the Mexican monsoon has piqued the interest of other scientists, including those researching drought conditions in the U.S. Midwest. Our approach is broader, looking at how air, sea and land interact. Donations to DRI's Annual Fund campaign helped sponsor their initial research. Now the pair hopes national scientific agencies will fund proposals to further pursue their unique approach. If those funds come through, it may mean that one day, people in Arizona and northwestern Mexico will look to the warm pool off southern Mexico for rainfall predictions instead of the Farmer's Almanac.