by John Simpson
October was cool and wet for southern Arizona. Most areas in Vail reported 2-3 inches of rain for the month. I recorded 2.59,” which is the wettest October at my place so far this decade. In fact, 4 of the last 8 Octobers, I recorded no rain. Therefore, this month was well above my 8-year October average of 0.79.” The Tucson airport recorded 2.87” which is the 5th wettest October since the 1880s and well above its 30-year average of 0.89.”
On the temperature side, October was cooler than average, aided by tropical storms, Pacific storms, and cold fronts. In fact, the daily high temperatures at the airport was at or below average from the 1st to the 19th. This was the first time in over 10 years the airport had a streak of high temperatures that did not go above average for nearly three straight weeks. In addition, only 1 day, the 28th, had a high 90 degrees or higher. This was the least amount of 90 degree plus days for October since 1984. Last year the airport had 25 days of 90 or better and 2016 had 26 days. Since October was very cool, 2018 to date has now slipped from the first to the third hottest year on record for Tucson. October 2018 also ended a record 24 consecutive months of above normal monthly temperatures at the airport.
Why was October so wet and cool? Two main reasons, tropical influence and Pacific storms. The remnants of Hurricane Rosa brought widespread rain from September 30th to October 2nd, mainly west of Tucson. This aided in both Ajo (5.77”) and Phoenix (5.35”) recording their wettest Octobers ever. Next, moisture from Hurricane Sergio brought several rounds of rain during the middle of the month. Sergio came in advance of a Pacific system that also brought rain and a strong weather system impacted the area on the 21st and 23rd. Lastly, a dry cold front cooled the area down for Halloween. I can remember many Octobers where no tropical systems, Pacific storms, or cold fronts ever arrived. These weather systems caused October 2018 to be cool and wet.
