September 2010 Climate Summary

Drought– Much of southeastern Arizona and southern New Mexico remain drought-free where abundant monsoon rains were observed. Drought conditions continue to worsen across northwest Arizona, where overall monsoon season precipitation has been spotty and generally below average.

Temperature– Temperatures during the last 30 days generally have been 0–4 degrees F warmer than average. Since the water year began on October 1, conditions have remained cooler than average in the Southwest.

Precipitation– The monsoon season is winding down. Precipitation in the last 30 days has been drier than average except in a few locations, including southeastern Arizona.

ENSO– A La Niña Advisory remains in effect, meaning that La Niña conditions are present across the equatorial Pacific Ocean. These conditions are expected to persist and possibly strengthen through the upcoming fall and winter seasons.

Climate Forecasts– Drier-than-average and warmer-than-average conditions are forecasted for all of Arizona and New Mexico through the winter. The ongoing and strengthening La Niña event heavily influences these outlooks.

The Bottom Line– The monsoon season shaped up to be near average in most parts of the Southwest but was unique nevertheless. High humidity, warmer-than-average nighttime temperatures, and a brief wet period between mid-July and mid-August defined this summer. In the past 30 days, drier- and hotter-than-average conditions covered most of the Southwest. Drought conditions, however, remained similar to last month, but may expand soon. The current La Niña event is moderate to strong, which portends drier-than-average winter conditions and is reflected in the most recent seasonal climate forecasts. Temperatures are also expected to be warmer than average, reflecting both the La Niña event and the warming trend observed in recent decades.