On Monday September 8th, the Phoenix Metro area experienced unprecedented flooding rains with widespread 3-4 inches and locally more than 6 inches of rain falling within about 6 hours. Since the normal rainfall for Phoenix is only a little over 7 inches in a year, it is evident what an extreme event this was. The culprit was a large influx of tropical air that was pushed northward into Arizona around the dying circulation of former Hurricane Norbert off the west coast of Baja California.
While the circulation of Norbert never came close to Arizona its influence was significant.
Below is a visible satellite photo taken at 9 am Tuesday clearly showing the remnants of Norbert spinning well off Baja.
Dr. Jim Steenburgh of the University of Utah in his blog provides an excellent discussion on the Phoenix flood event of September 8 2014.
Tuesday, September 9, 2014
Intense excitement prevailed yesterday as heavy rains brought flooding to locales such as Palm Springs (CA), Las Vegas (NV), the Virgin River Gorge (UT), and Phoenix (AZ). Given the large spatial contrasts that exist in monsoon precipitation, the event was about as widespread as a monsoon precipitation event can get.
Phoenix has gotten a great deal of attention and for good reason. The Phoenix Airport recorded 3.29″ of rain for the day, all falling in about 7 hours. Accumulations of over 2 inches covered a large portion of the metropolitan area with some locations reporting more than 5 inches.
The time series of accumulated average (brown line) and actual (green line) precipitation since the start of the water year (October 1, 2013) shows the feast or famine nature of the Arizona climate. Average looks nice and smooth, but in any given year, a few storms produce most of the precipitation. Indeed, you can see three major cool season events, a couple of small monsoon events in August, and then yesterday’s whopper add up to an “above average” water year at this location.