Through August 25^th, only 0.70" of rain has fallen at Phoenix Sky Harbor Airport this monsoon season. The new Phoenix Rainfall Index (PRI) has measured 0.43" so far this monsoon season. The table below shows the PRI since 1999 for June 15^th through August 25^th and how it compares to observed rainfall at Phoenix Sky Harbor.

During the past 30 years (1979-2008), the average precipitation during that same period, June 15^th through August 25^th, was 1.87". The wettest monsoon season through August 25^th was in 1911 when 7.47" was measured while the driest was in 1914 and 1993 when 0.22" of rain fell (see Top 10 tables below). The chart toward the bottom shows how, at Sky Harbor, 2009 compares to average and the wettest/driest year on record.

From all of these datasets, we can easily see that the monsoon season of 2009 remains slow to get going. With much of the season behind, the likelihood of significant rainfall is diminishing. However, that can quickly change during September due to the increased climatological possibility of precipitation enhancement from Eastern Pacific tropical systems. That probability is slightly enhanced this fall due to the El Niño conditions in the Pacific.