Missing Middle of the Monsoon

Every year in Tucson people complain about the current monsoon—not like the ones they remember. That's an accurate perception; it isn't just a matter of recalling only the spectacular days. Each monsoon has a different variety. Some years feature squall lines that roll across the metro area between 3 and 5 pm, others chaotic distributions of evening storms, others organized nocturnal systems, others breaks when the monsoon completely shuts down—each of these more frequently in some years and less in others. So judging this year is not like the others is usually justified.

It's generally recognized and understood that during the shoulder seasons of the monsoon, early July and the weeks around Labor Day, rain totals can be erratic. Erratic is even better understood for the off-seasons, late June and mid-late September. Intrusions of tropical moisture if they happen in the off-seasons are appreciated; if not, oh well. But usually over a four week period near the middle of the monsoon, the last half of July and the first half of August, one way or another the idiosyncrasies of that year's monsoon generate a rain total that meets expectations. That did not happen this year. (My house is 12 miles north of the Tucson Airport.)

2018 Period	# days	My house, inches	Airport, inches
June 15 and 16	2	1.76	0.91
July 5 to 15	11	0.98	1.77
Jul 16 to Aug 13	29	1.01	1.15
Aug 14 to Aug 25	12	1.26	2.05

Until two weeks ago this year the usual quips about the non-soon had given way to bitter comebacks, What monsoon?!, or as someone on my community's listserve wrote sarcastically on August 11, Our trees/shrubs are just loving it!! G RRRR!

Since the current official definition of the monsoon includes June 15, as well as all of September, and since September is expected to be above normal, it's likely that the official rain total for this year's monsoon will look reasonable. But no matter how much rain arrives in September, it won't wash away the reality of a missing (less than 0.04 inch per day) middle of the monsoon this year.

Elusive Effects of El Niño

Seems only yesterday, but it's been three years since everyone was talking about expectations for the then upcoming 2015-2016 winter. That summer of 2015 the Oceanic Niño Index (ONI, defined and calculated by the Climate Prediction Center [CPC]) had already run past plus one, and was expected to (and did) exceed plus two during the winter of 2015-2016. This year the latest Diagnostic Discussion by the CPC places the odds for El Niño at 60% this fall, and 70% during the upcoming winter. The CPC's consensus of forecasts takes the ONI to around 0.6 by this October and to about 1.0 during the winter.

This time three years ago I thought that the chatter about the upcoming effects of El Niño was excessive. This summer on the contrary it seems that excessive reticence has replaced overconfidence. Three years ago in an initial rant about the chatter, I posted a scatterplot of the previous 65 years of precipitation at Tucson airport, totaled for September combined with October, versus October ONI. Here are the final numbers for the last three years—an additional three points that can now be added to that scatterplot for fall.^*

Year	October ONI	September plus October Rain, inches
2015	+2.4	4.65
2016	-0.7	1.70
2017	-0.7	0.03

I won't rehash my old rants about fall; they can be read from three years ago here, and two years ago here. The point about expectations for this fall is that to the extent that an increased level of concern about the kind of thing that can happen in the fall because El Niño was justified three years ago, that level of concern is equally justified this year.

There will be a separate post for winter, including a fresh scatterplot^* for that season, as well as wonderings about why the scatter for that season is what it is. But that post can wait for a month or two.

* The plots three years ago were made with the previous version (v4) of the CPC's ONI's SST anomalies. The current version (v5) mostly differs by no more than 0.1 ONI (degree C), but in some cases the difference is 0.2 or even 0.3. Notably: October 1983 is now -0.8 (previous -0.6); and January 2010, which previously at +1.3 was right in the middle of the "moderate" El Niño category, now at +1.5 edges into the strong category.