Heat and humidity are peaking yet again in Phoenix and across the Southwest after Labor Day weekend, with heat alerts in effect through the work week for some.
High pressure will shift back west from the southern Plains, sitting directly overhead of Arizona by Wednesday, Sept. 9, raising highs between 105 to 109 degrees in Phoenix. Hotter temperatures near 110 are possible in southwestern Arizona and southern California. Overnight lows are expected to range throughout the 80s, not falling much due to evening and nighttime cloud cover.
Extreme heat warnings are in effect in south-central, southwestern and western Arizona along with much of southern California. The beginning and end vary by region and the leading weather office, but in metro Phoenix,
the warning began Tuesday, Sept. 8 and lasts through Thursday, Sept. 10.
These warnings may not seem warranted after a summer with 39 days at or above 110 degrees, but the real killer this time is the humidity. Dew points in south-central/southwestern Arizona and southern California are reaching the mid-70s in cities from Phoenix to Los Angeles. It’ll make the region’s heat indices feel hotter than Miami during some afternoons.
As seasonal temperatures slowly cool off of summer’s worst heat, the thresholds for extreme heat change as well. During the first two weeks of September, the normal high in Phoenix falls from 104 to 101 degrees. So while it may not be uncommon to have temperatures near 110, that level of heat and humidity are riskier during this time of the season.
During the hot part of the week, rain chances are near-zero in the Valley, but scattered chances exist in the high terrain of eastern and southeastern Arizona. As the high pressure’s strength weakens on Thursday, Sept. 10, outflows have a better chance of making it to lower deserts and spawning some thunderstorms. The best odds are on Friday evening, Sept. 11.
Meteorologist Tevian Whitehurst covers extreme weather and climate for The Arizona Republic and azcentral.com. Follow him at @TevianWX on Instagram and Facebook (Meteorologist Tevian Whitehurst).
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This article originally appeared on Arizona Republic: Extreme heat warnings come with tropical-like weather in the Southwest
