Severe Thunderstorm Warning 288, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
1220 PM MST Thu Sep 24 2026

.SYNOPSIS...The chance of showers and thunderstorms continues today,
with the stronger thunderstorms producing heavy rainfall and an
isolated threat of flash flooding. Drier air then overspreads
southeast Arizona Friday and Saturday. Moisture moves back into the
area late in the weekend and early next week, for a return of the
chance of showers and thunderstorms. High temperatures will be a
couple of degrees below normal today, warming to slightly above
normal over the weekend and then lowering several degrees below
normal early to mid next week.

&&

.DISCUSSION...The large scale pattern has a baggy trough to our west
and high pressure aloft centered along the far eastern Texas Gulf
Coast. A storm system will move across the northern tier of states
Friday and Saturday, flattening the upper high and shifting it over
the Gulf. A low pressure system and associated trough will then move
across central California and the Great Basin early next week as
Hurricane Polo moves northwestward to along the Baja Mexico coast.

The showers and thunderstorms earlier today across central/western
Pima County were in response to a mid level disturbance now parked
over far southwest Arizona. The models lift this disturbance slowly
north/northeast across Arizona later today. PWATs hold steady in the
1.0 to 1.3 inch range today, with isolated to scattered showers and
thunderstorms developing during the afternoon hours mainly east of a
Nogales to Sells line. The high res models then lift these showers
and thunderstorms to the northeast across the eastern portion of the
forecast area through the evening hours tonight. The stronger
thunderstorms will be capable of producing heavy rainfall and an
isolated threat of flash flooding.

Drier air begins to overspread southeast Arizona from the west on
Friday, as the flow turns southwest/west in response to the system
tracking east across the northern tier of states. There will still
be a slight chance of showers and thunderstorms on Friday across far
eastern areas along the New Mexico state line. However by Saturday,
PWATs lower down into the 0.60 to 0.80 inch range and shut down
convection chances across southeast Arizona.

Sunday into early next week, the combination of an upper low/trough
moving into the West Coast and Hurricane Polo moving northward along
the Mexico coast will help spread moisture back across southeast
Arizona from the south. This moisture begins to move back into the
area on Sunday, with deeper moisture moving in Monday and Tuesday
and a chance of showers and thunderstorms across all of southeast
Arizona. The NHC official track for Hurricane Polo now shows Polo
moving west of the Baja Peninsula tip late Sunday and then curving
eastward into central Gulf of California south of the Baja Spur by 6
AM Tuesday. While Polo will help push moisture northward through
Mexico as it tracks north, this track/timing will have little direct
impact on southeast Arizona as most ensembles continue to curve Polo
eastward into central Sonora to the south of Hermosillo. The current
NHC track/timing would put Polo on the back side of the trough axis
swinging through the region, which would then shunt Polo remnants
northeast across northern Mexico and into New Mexico and west Texas.
While there is still some uncertainty in the exact track/timing of
Polo, what may be a bigger player in our weather early next week
(than the Polo remnants) will be sharp trough dynamics interacting
with the moisture in place across southeast Arizona as this system
moves across the region.

Behind the trough, there will be a slight chance of showers and
thunderstorms along the International Border/New Mexico state line
on Wednesday of next week. High pressure aloft then builds over the
eastern Pacific Ocean and southeast Arizona dries out significantly
under westerly flow for the end of next week. Both the calendar date
(October) and moisture profile reflect the end of Monsoon 2026.

Overall, high temperatures will be a couple of degrees below normal
today, warming to slightly above normal over the weekend and then
lowering several degrees below normal early to mid next week.

&&

.AVIATION...Valid through 26/00Z.
SCT-BKN clouds at 6k-9k ft AGL. ISOLD-SCT -TSRA/-SHRA thru 25/04Z
then a slight chance of -TSRA/-SHRA east of a KALK to KSAD line
again aft 25/18Z. Gusty winds to 40 kts, heavy rain with low
visibility and mountain obscurations possible with the -TSRA. SFC
wind SELY/SLY thru 25/18Z, with a SWLY to NWLY in direction aft
25/18Z. Outside of any -TSRA, SFC wind less than 12 kts thru the
valid period. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A chance of showers and thunderstorms continues
into tonight, with the stronger thunderstorms producing heavy
rainfall and an isolated threat of flash flooding. Drier air then
overspreads southeast Arizona Friday and Saturday. Moisture moves
back into the area late in the weekend and early next week, for a
return of the chance of showers and thunderstorms. High temperatures
will be a couple of degrees below normal today, warming to slightly
above normal over the weekend and then lowering several degrees
below normal early to mid next week. Minimum RH values will be in
the 17-30 percent range from Tucson westward through the middle of
next week, with values in the 27-40 percent range east of Tucson
(even higher in the mountains). 20-foot winds will be less than 15
mph into early next week. Gusty and erratic winds will be possible
with any thunderstorm.

&&

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

&&

Zell

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