The hot, dry weather dominating Arizona and the Southwest during the last week had a direct effect on the historic rain and flooding in Texas from what was Hurricane Harvey.
“There were two high-pressure systems, one to the east of the hurricane and one to the west,” said Nancy Selover, Arizona state climatologist, in a statement. “Those and the low-pressure trough between (them) sort of trapped Harvey, keeping it in place.”
“Typically, hurricanes fall apart within hours, because they get cut off from energy source once over land,” said Michael Crimmins, University of Arizona associate professor of global change and soil, water and environmental science.
But Harvey stalled and continuously drew in huge amounts of warm water onto land. The storm even moved back into the Gulf of Mexico to gather more steam as it began its path to the northeast.
More than 50 inches of rain — historic totals — fell in some places in and around Houston.
All the while, Tucson saw below-average rainfall — only 0.13 of an inch — and somewhat higher than average temperatures during the last week. Since Saturday, Tucson has seen highs of about 5 to 6 degrees above normal for this time of year, according to the National Weather Service.
Our weather system also had another impact — keeping out of Harvey’s rainy reach.
“The high pressure to the west was over us, and is keeping most of Harvey’s moisture from getting to Arizona,” Selover said.
This configuration of high-pressure systems had a specific effect in keeping Harvey stalled over the Houston area as opposed to what typically might have happened.
“Had the subtropical high over the Southwest been stretched across all the southern United States — it can sometimes have this configuration — Harvey would have blasted west into Texas and decayed rather quickly over the mountains of Mexico,” Mark O’Malley, meteorologist at the National Weather Service in Phoenix, said in a statement.
As the high-pressure system in the eastern United States let up, Harvey moved over Louisiana, and began weakening in its path across Mississippi, Tennessee and Kentucky. By Thursday morning, Harvey was a tropical depression and was expected to move across the Ohio valley by Saturday as a post-tropical low, according to the National Hurricane Center.
In Tucson, “we turn our attention now to (Tropical Storm) Lidia at the Gulf of California,” Crimmins said, which might break the dry spell and bring moisture next week.
“Monsoon’s not over,” he said. “It’s getting close but there’s one or two surprises left.”
It will remain warm through next week in Tucson with highs in the low 100s on Saturday and Sunday and near 100 Monday through much of next week, according to the NWS. The chance of rain was at 10 percent for the weekend.
Our monsoon season officially ends Sept. 30.