Monsoon Summary

The monsoon season is winding down  and officially ends on September 30 in Arizona. During the last month, hotter and drier-than-average conditions characterized many regions in the Southwest (see this month’s feature article). Most areas received less than 70 percent of average precipitation, with the exception of southeast Arizona, where copious rainfall around the mountains dropped between 150 and 200 percent of average. Reviewing the season’s precipitation totals reveals that most activity occurred during a four-week window between mid-July and mid-August. Despite a late start and drier-than-average end to the season, the three-month totals between June 16 and September 13 reflect near-average monsoon rainfall conditions for many parts of Arizona and New Mexico (Figures 8a–c). Since September 13, moisture incursions from the Gulf of California have produced typical isolated thunderstorms, but have not generally increased precipitation totals .  Between June 15 and September 16, rainfall totals in southeast Arizona have been near average, tallying 5.44 inches in Tucson, 8.15 inches in Nogales, 11.17 inches in Sierra Vista, and 7.00 inches in Wilcox.

The monsoon season was also characterized by warmer-than-average temperatures during the day and night. The daily low temperatures, which reflect night conditions, were on average 3 degrees F warmer than average in both states during June through August; Phoenix nighttime temperatures in July were around 4 degrees F warmer than average. Long gaps in monsoon storms and the general summer warming trend likely account for these conditions, according to the National Weather Service in Phoenix.