As July kicks off, the annual Southwest monsoon season is gearing up to bring heavy rain to the region. Recent downpours have already been observed in parts of New Mexico. A shift in weather patterns is expected across the western U.S. in the coming days, with the Northwest experiencing a brief heat wave that will gradually subside. Concurrently, a weak low-pressure system will move towards the Pacific Southwest, ushering in increased moisture flow next week.
Additional moisture is anticipated to come from the tropics, with a tropical system likely forming south of Mexico over the weekend and into the following week. While some details remain uncertain, computer models suggest this system will approach Baja California with a substantial amount of moisture.
The Southwest monsoon is characterized by a seasonal shift in wind direction, rather than individual thunderstorms. This wind change, from westerly to southerly, facilitates the influx of moisture from the Eastern Pacific and Gulf during the summer wet phase. The onset of the monsoon varies annually, typically starting on June 15 but intensifying in late June or July. Thunderstorm activity fluctuates in intensity from day to day throughout August and September.
The monsoon is a crucial source of rainfall for the Southwest, providing over half of the annual precipitation in northwestern Mexico and the southwestern U.S. However, it also brings challenges such as dust storms, flooding, and lightning. Dust storms, or haboobs, can reduce visibility and impact air quality, while flash floods can occur in canyons and arroyos even during dry conditions. Lightning strikes can ignite fires until the ground becomes saturated.
Periodically, hurricanes can enhance monsoonal moisture levels by drawing in remnants from former Eastern Pacific tropical storms or hurricanes. Notably, Hurricanes Kay in 2022 and Hilary in 2023 triggered flooding in California. Jonathan Belles, a digital meteorologist with weather.com for 9 years, is passionate about tropical weather and covering high-impact events, including winter storms. He holds degrees from Florida State University and St. Petersburg College.
