Monsoon winds are seasonal changes in the direction of the prevailing winds of specific regions. They are caused by the unequal heating rates of oceans and continents.
These winds blow from cold to warm areas. Summer monsoons, accompanied by torrential rains, cause the rainy season in the tropics, especially around the Indian Ocean.
Winter monsoons bring dry cooler air from China and Mongolia. However, this air flow is reduced by the Himalaya Mountains, keeping southern India and Sri Lanka warm year-round. Winter monsoons may be associated with drought.
The North American monsoon happens once a year, in summer. When warm, moist air from the Gulf of California meets warm, moist air from the Gulf of Mexico, rain falls on the Sierra Madre in central Mexico.
Nearby desert regions get moisture from this system, which can aid firefighters as they combat wildfires in Arizona, where summer temperatures regularly reach 38 degrees Celsius.