Summer 2023 ended as the hottest on record in Phoenix, and now the 2023 monsoon season will end as the driest.
During a summer of unprecedented and prolonged heat in metro Phoenix, many people had eagerly waited for the monsoon season to begin and fend off the scorching temperatures. But aside from a few storms that offered temporary reprieves, monsoon precipitation was weeks delayed and below average.
The monsoon season officially ends on Saturday having produced fewer storms overall than previous years, especially in central and southeastern Arizona.
Although parts of the state depend on the monsoon for much of their annual rainfall, lack of precipitation during this season will not endanger water supplies, especially following a wet winter and the strengthening of El Niño conditions.
Here’s some of what to know about the monsoon:
How much rainfall did Arizona get during the 2023 monsoon?
Phoenix posted its driest monsoon ever, with just 0.15 of an inch of rainfall at Sky Harbor International Airport, compared to a 2.28-inch average. While rain gauges in other parts of metro Phoenix recorded higher totals, the airport reports the official figure.
Statewide, the 2023 monsoon was hotter and drier than previous years. While season totals have not yet been released, based on figures from June, July and August, it was the 20th-warmest and 10th-driest season. (The monsoon season starts June 15 and ends Sept. 30, while meteorological summer covers June, July and August.)
Although residents of central and southeastern counties experienced an exceptionally arid monsoon, precipitation in the north and west offset the drier areas.
“Fortunately, this monsoon season was dry but not the driest. The 2020 ‘nonsoon’ season remains the precipitation loser,” said Erinanne Saffell, director of the Arizona State Climate Office and the state climatologist, regarding 2020’s status as the driest monsoon.
Tucson and Flagstaff also recorded below-average precipitation. As of Sept 26, Tucson fared the best with 4.73 inches of rain compared to a 5.39 average between 1991 and 2020. Flagstaff had 4.24 inches of precipitation compared to a 7.2-inch average.
The monsoon typically accounts for about half the yearly rainfall in the central and northern regions and roughly two-thirds to three-fourths of annual precipitation in southern Arizona.
Northern and western counties saw more rain than usual, particularly Yuma, Mohave and Coconino counties. Remnants of Tropical Storm Harold (which originated in the Atlantic Ocean) and Hurricane Hilary (which developed in the Pacific) played a role in bringing more precipitation to these areas.
Why was Arizona’s monsoon delayed?
It took weeks for monsoon thunderstorms to develop, which is a key reason why some areas saw less rain. The Arizona monsoon season begins on June 15, but storms did not arrive in central and southern counties until mid-to-late July.
Monsoon storms need two key elements to occur: a northward wind shift that brings in summertime moisture from the Pacific and the Gulf of Mexico, and high daytime temperatures. Together, intense surface heating and increased moisture produce monsoon thunderstorms during the summer.
The first storms generally require three consecutive days with a dew point higher than 55 degrees and temperatures between 100 and 108 degrees to develop. Typically, temperatures over 100 degrees in June help build a high pressure, subtropical ridge that summons moisture from the south. Arizona’s abnormally cool June delayed the onset of the monsoon by about six weeks.
This hot high-pressure ridge settled over central Arizona instead of the Four Corners, where it typically stays during the monsoon, bringing moisture through the state.
“When you’re underneath that bubble of heat, there’s really not much moisture, and the opportunity for thunderstorms is limited,” said Michael Crimmins, a climatologist from the University of Arizona. “When the monsoon doesn’t behave correctly, we can get into these really nasty heat spells.”
And yes, the lack of monsoon storms contributed to the 31-day streak of high temperatures at or over 110 degrees in Phoenix. Monsoon showers typically offset the heat in July, and the record-breaking heat wave finally came to an end on July 31 following storm activity.
Because the high-pressure system stalled over central Arizona, western and northern areas around the edges of the system saw some precipitation. Along with tropical storm activity, this subtropical system spurred more rainfall in the north and west.
Despite a lackluster monsoon, the state overall is on track for an average water year. The water year spans from October 1 to September 30, coinciding with the end of the monsoon, and tracks statewide precipitation during that time.
Based on data collected from 1896 to 2022, the average annual precipitation in Arizona is 12.26 inches. Between October 2022 and August 2023, the state had 11.43 inches of rainfall, and experts hope September’s precipitation will bring numbers even closer to the annual average.
Does below-average monsoon rainfall affect water levels?
While every drop counts during Arizona’s ongoing 23-year drought, the state does not rely on the monsoon to replenish its rivers and reservoirs. Watershed from snowmelt is the backbone of the Colorado, Salt and Verde river systems.
During the 2023 monsoon, Salt River Project’s watershed had its second-driest season. As of Sept. 17, SRP reported a combined watershed rainfall of 3.45 inches, 61% of the average precipitation.
SRP’s reserves are still high following winter storms that brought above-average snowmelt to Arizona. The SRP system is at 86% of capacity, compared to 65% during the same time last year.
“It’s not operationally something that we are concerned about, especially given that it was on the heels of an incredibly productive and wet winter, which completely filled our reservoir system,” SRP meteorologist Jesus Haro said.
Precipitation from the monsoon helps alleviate downstream demand from water sources and can affect releases from lakes and reservoirs. For example, the Bureau of Reclamation temporarily increased the minimum amount of water released hourly from Glen Canyon Dam on Sept. 14 to improve boater safety in the absence of monsoon showers.
You thought AZ’s summer was extreme?A ‘strong’ El Niño could supercharge winter
Did El Niño play a role in the monsoon?
In June, scientists from the National Weather Service declared an El Niño Advisory, saying they observed El Niño weather conditions and expected them to strengthen through 2023 and into 2024.
El Niño is a climate phenomenon that creates above-average sea surface temperatures in the Pacific Ocean near the equator. It usually occurs every three to five years and lasts for nine to 12 months. While it is difficult to predict the exact weather implications, El Niño events can impact weather patterns that trigger heavy rainfall and droughts around the world.
Experts say it is hard to determine El Niño’s impact on summer weather, but it may contribute to higher summer temperatures and delay the monsoon because it can weaken and reposition the subtropical ridge that summons moisture from the south.
While this summer was drier than normal, climatologists are hopeful for another wet winter. Out of the nine El Niño events since 1994, seven brought above-average precipitation in Arizona during the winter.
“Statistically, we tend to get more precipitation in the winter when we have an El Niño event,” Saffell said. “How much? We don’t know how much is going to come out of the sky, but we’re all crossing our fingers.”
