Flash Flood Warning 171, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
235 PM MST Sun Aug 30 2026

.SYNOPSIS...Expect daily thunderstorms through at least Monday
with storms capable of strong to severe wind gusts and heavy
rainfall. After Monday storm chances begin to decrease. High
temperature will be below normal to start the week then near
normal Wednesday into next weekend.

&&

.DISCUSSION...Type IV Monsoon pattern in place today with the
upper high well to our east and an upper level trof along the
California coast. This pattern usually brings an increased
threat of severe storms, flash flooding, and nocturnal storms.

Storms a little slower to get going this afternoon, which was not
overly unexpected with some overnight activity and morning cloud
cover leading to the delay. PWATs across the area this afternoon
ranged from near 1" along the AZ/NM border to 1.70" across western
Pima county. Once storms get going, the main concern will be strong
to near severe winds, heavy rain with potential rainfall rates with
some of the stronger cores being 1-2"/hr leading to flash flooding,
especially west of Tucson, which was hit rather hard last evening.
Flash flood watch remains in effect until 5 am Monday for Pinal,
Pima and Santa Cruz counties.

Water vapor satellite imagery this afternoon showed a weak upper
level short-wave trof along central-CA coast. This feature will
continue to move east over the next 24 hours and extend from ern NV
south to SW AZ. Dynamics from this feature may produce some storms
around sunrise west of Tucson otherwise looking for another day of
scattered showers and thunderstorms, with main threats being heavy
rain and flash flooding, especially west of Tucson. In
anticipation of heavy rains across the Tohono O'odham nation
tonight and again on Monday aftn/eve, decided to extend the
flash flood watch for the nation through 10 pm Monday.

Tuesday and Thursday: Low-grade monsoon days as the monsoon
calendar turns to September and possible tropical influences
during the month.

Speaking of the tropics, NHC is monitoring a tropical wave with
disorganized showers and thunderstorms well south of SW Mexico. This
may become the next named eastern Pacific tropical storm late this
week with some model guidance (30/12z GFS) indicating that the
potential track will be further east than where current Tropical
storm Karina is at, and possibly closer to Baja by the end this week
into next weekend. Confidence low this far out on how much tropical
moisture would be advected across the area but something to keep an
eye on.

Temperature wise, below normal highs to start the week then near
normal highs Wednesday into next weekend.

&&

.AVIATION...Valid through 01/00Z.
SCT -SHRA/-TSRA thru 31/06z, bcmg ISOLD btwn 30/06z and 30/12z.
Chance of storms returning to the area aft 31/20z. Outflow SFC winds
nr TSRA 35-45 kts otrw SFC winds mostly less than 10 kts and terrain
driven. Clouds thru much of valid pd, SCT-BKN 8k-12k ft AGL.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Expect scattered afternoon and evening showers
and thunderstorms through Monday (30 to 70 percent daily
thunderstorm chances). There is also a chance storms continue
overnight Monday. Storms will be capable of strong to severe wind
gusts and heavy rainfall. After Monday storm chances and coverage
decrease with activity mainly from Tucson south and eastward.
Temperatures will be around normal today through the coming work
week. Minimum relative humidity values mainly 20 to 45 percent in
the valleys and 30 to 60 percent in the mountains over the next
week. Winds will generally remain less than 15 mph and terrain
driven through the week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
 Flood Watch through late tonight for AZZ503>507-513>515.
 Flood Watch through Monday evening for AZZ502.

&&

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