September 2018 was the hottest September on record in Tucson, according to the National Weather Service.

Fall is already here, but summer went out swinging.

Last month was the warmest September on record in Tucson, according to the National Weather Service, marking 24 straight months of above-average monthly temperatures.

The monthly average temperature in September was 84.9 degrees, 3.3 degrees above average. The previous high was set in September 2000, when the monthly temperature reached 84.8 degrees.

For 11 straight days, between the 8th and the 18th, the high at Tucson International Airport, the NWS official recording station, was 100 degrees or hotter. The monthly high was 105 on the 14th and 15th.

“In the middle of the month, we were under the influence of a high-pressure system,” said Aaron Hardin, meteorologist at NSW Tucson, which can happen as the monsoon transitions out. “”It’s not a favorable pattern and scours out moisture and keeps us hot.”

The monsoon season ended Sunday. The remnants of Hurricane Rosa brought Monday’s rain.

The 11-day heat streak fell only one day short of surpassing the 1955 record for the most triple-digit highs in September. None of the other record-holding, triple-digit streaks have trended so late in the month.

Every day was above 90 degrees except for two, the 19th and 20th, after a spat of rain caused by a tropical storm temporarily cooled things off.

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Looking at October, a low-pressure system should keep things cool in the first part of the month, Hardin said.

But fall temperatures overall could trend slightly above average, according to the Climate Prediction Center, so we should enjoy the cool weather while it’s here.

And in case you’re wondering, 2018 is, so far, the warmest year on record for Tucson, coming in at 75.4 degrees.

Contact Mikayla Mace at mmace@tucson.com or 573-4158.