The NWS-defined "Monsoon Season" runs from June 15th through September 30th and has now come to an end. The old NWS dewpoint-based definition (three consecutive days with average Td of 54 F or higher defined the onset of the monsoon - ending was ambiguous and subjectively determined by NWS staff over the years) was replaced with the generic seasonal approach a number of years. The seasonal approach means that any rainfall occurring from June 1st through September 30th is added to the monsoon total, regardless of the synoptic pattern that produced the precipitation event. I think that this approach is vague, sloppy, and meteorologically inhomogeneous, but it clearly is easy to apply.
However, it is still useful to examine the average daily dewpoint temperature at the TUS observation site (above from NWS for 2017 monsoon season). The longest period during which the daily Td was above average, and also above ave Td of 54 F, extended from July 10th through August 5th. During the period July 10th through 22nd the bulk of monsoon precipitation fell - 5.46 inches or 72% of the season total (I'm using rainfall recorded here at house). One significant event occurred on August 12/13 when 1.16" fell within a westerly flow synoptic regime, and that was essentially the end of the precipitation for the season (87% of the seasonal total - which occurred on 9 precipitation days). There were also only 9 days during the monsoon season (a 107 day period) with 0.25" of rainfall or more - four of these days had rain amounts here of over an inch. We are in the Sonoran Desert and extreme variability is certainly the norm.
My records start in 1999, and this just-ended September was the driest of my short period of precipitation data. The period from August 15th through September 30th was also the driest in my records. However, the very wet July period and the one August event made this the 7th wettest June through September period here at the house.
The results for TUS observations are very similar, as shown by Mike Crimmins comprehensive summary diagrams below. Better legibility at:
https://cals.arizona.edu/climate/misc/monsoon/monsoon_summaries.html
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