The North American Monsoon is a seasonal pattern of increased rainfall that occurs in the southwestern United States and northwest Mexico during the summer months. This phenomenon is primarily driven by the shift in wind patterns and the influx of moisture from the Gulf of California and the Gulf of Mexico. The North American Monsoon typically begins in late June or early July and lasts until September, bringing much-needed precipitation to the typically arid regions of the southwest. Scientists study the North American Monsoon to better understand its variability, predictability, and impacts on water resources, agriculture, and ecosystems in the region.