Monsoon 2018 was drier than usual in Phoenix

With the aftereffects of Hurricane Rosa dominating the Phoenix weather scene, it’s easy to forget about the justended 2018 Arizona monsoon season.

The monsoon ended Sunday with a little more rain courtesy of Rosa. Remnants of the storm wouldn’t be considered classic monsoon moisture, but any rain that falls from June 15 to Sept. 30 counts.

Phoenix saw 2.63 inches of rain for the monsoon (defined by the National Weather Service as June 15-Sept. 30

since 2008). That’s 0.08 of an inch below normal for that period. The record wettest monsoon saw 9.56 inches in 1984, while the driest was 0.35 of an inch in 1924.

While Phoenix was a bit below normal, Flagstaff, Kingman and Tucson were all on the wetter side.

Flagstaff saw 9.97 inches of rain for the monsoon, 1.66 inches above normal. Kingman recorded 3.07 inches for the season (2.82 inches is normal) and Tucson picked up 7.02 inches, compared with the normal of 6.08 inches.

Yuma was also below normal, with 0.89 of an inch compared to that city’s normal total of 1.29 inches.

Elsewhere in the Southwest, Albuquerque (4.83 inches vs. 4.61) and Palm Springs (0.95 of an inch vs. 0.65) were a bit above normal for the season while Las Vegas (0.87 vs. 1.01) and El Paso (4.04 vs. 5.14) came up a little short.

Monsoon rains could start to ease some of the short-term (surface) drought conditions that have ratcheted up in the past year.

University of Arizona climate scientist Mike Crimmins explained that it would take a while to make that determination.

“I think we’re now at the point where we’ll start to re-evaluate the current drought status around central Arizona,” said Crimmins, who also works with the U.S. Drought Monitor. “The parts of Arizona that had such good, solid monsoons and are now under the track of Rosa are going to start to see improvements in the short-term drought conditions. The far northeast part of the state, it’s going to take a little longer because it didn’t have much of a monsoon.”

With the possibility of El Niño conditions developing in the eastern Pacific Ocean, there may be more storms like Rosa that could impact Arizona’s fall weather.

El Niño conditions mean there are warmer-than-normal waters in that part of the Pacific Ocean. Storms thrive in those warmer waters.

“(The Climate Prediction Center) was expecting an above-average (hurricane) season and that’s certainly what happened,” Crimmins said. “Now that we’re in the transition from the summer monsoon into fall, that area is still very warm and kicking off storms about once a week. It’s possible, at least into the first few weeks of October, to have another event like that occur.”

Sergio, a tropical storm as of Monday afternoon, could develop hurricane strength. Its current path isn’t predicted to impact Arizona, but that could change.

“It’s a little early to see if that will happen,” Crimmins said. “But it could follow a similar path to Rosa and we could see another slug of moisture like we’re seeing now.”

Through the end of September, Phoenix is well behind the pace for total rainfall for the year, at 3.40 inches.

Normal for the first nine months is 5.92 inches.