Heat in Arizona, September 15 to 17, 2025

Area Forecast Discussion
National Weather Service Tucson AZ
812 AM MST Mon Sep 15 2025

.SYNOPSIS...Moisture slowly moves in this week leading to
isolated to scattered showers and thunderstorms south and east of
Tucson through the middle of the week. Storm coverage increases
later in the week. Temperatures will be slightly above normal
through the middle of the week, then around normal late this week.

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.UPDATE...
Mostly clear skies this morning with some very isolated light
showers to the east of Tucson. This afternoon , 25-35% chance for
isolated showers and thunderstorms focused south and east of
Tucson. Dry air that moved into the area yesterday remains mostly
in place today. Satellite derived PWATs are around 0.5 to 1 inches
across southern Arizona this morning. Temperature will increase
slightly from yesterday with highs around 95 to 100 degrees with
Minor HeatRisk.

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.PREV DISCUSSION... /issued 244 AM MST Mon Sep 15 2025/

.DISCUSSION...High pressure is centered to the south over northern
Mexico with a small upper level low off the coast of Baja. The
placement of these two features will allow moisture to slowly
move into southeast Arizona through the work week. GOES 19 total
precipitable water is already showing this with PWATs increasing
by about 0.2" over the last few hours. Enough moisture will move
in today for isolated storms south and east of Tucson. Hi-res
guidance shows the best chances will be along the international
border in Santa Cruz and Cochise Counties. PWATs will only be
around 1" so heavy rain won't be a threat but storms will be
capable of some gusty winds. Tuesday PWAT increases to around
1.25" over most of the CWA which will lead to an increase in storm
chances and coverage. This is backed up by HREF members which
show scattered thunderstorm coverage over much of the area except
for Pinal County. The best chances will be in Santa Cruz and
Cochise Counties. With the added moisture heavy rainfall will
become a threat especially in Santa Cruz County which the 15/00Z
HREF puts under the greatest threat. Models show a slight
reduction in activity Wednesday, but still expect there to be
isolated thunderstorms especially along the international border.
The high pressure to the south will increase heights over
southern Arizona leading to temperatures a few degrees above
normal today and Tuesday.

Thursday into Friday the upper low off Baja moves northward
allowing a long fetch of southerly mid-level winds that advect
tropical moisture into southern California and southern Arizona.
This brings PWATs to 25-75 percent above normal with the most
anomalous moisture west of Tucson. This will lead to an uptick in
storm activity Thursday mainly from Tucson south and westward
then expand to encompass all of southeast Arizona Friday. Still
some uncertainty with how far east the low will end up as it moves
north. The further east it ends up then the further east the
anomalous moisture will be, which would increase PoPs and the
heavy rainfall threat. The added moisture will also bring
temperatures down to around normal Wednesday into the weekend.

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.AVIATION...Valid through 16/12Z.
SCT-BKN clouds 6k-10k ft AGL through the period with greatest
coverage along the international border. Isold TSRA will be
possible this afternoon over Santa Cruz and Cochise Counties. Wind
gusts 30-40 kts possible near thunderstorms. Otherwise Sfc winds
west to northwest 5-10 kts this afternoon and evening and
variable less than 8 kts at other times. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Minimum RH values in the 15-30 percent range
today, then 20-35 percent thereafter. Isolated thunderstorms
possible today in Santa Cruz and Cochise Counties with greater
coverage and chances Tuesday afternoon. Storm chances decrease
some Wednesday then increase Thursday and Friday as more moisture
moves in. 20-foot winds will be 8-12 mph with some afternoon/early
evening gusts to around 20 mph over the next week.

&&

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.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&

Malarkey

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