Moisture from the remnants of tropical system Nora produced moderate to heavy rainfall during the afternoon and evening hours with totals of 1 to 2 inches common and up to 3 inches in mountains, but the prolonged nature of the rain led to little if any significant flooding. However, flash flooding did occur along the Artesia Wash west of Sells where heavier rain fell in a shorter amount of time.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS TWC wrote it up.
Moisture from the remnants of tropical system Nora produced moderate to heavy rainfall during the afternoon and evening hours with totals of 1 to 2 inches common and up to 3 inches in mountains, but the prolonged nature of the rain led to little if any significant flooding. However, flash flooding did occur along the Artesia Wash west of Sells where heavier rain fell in a shorter amount of time.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Tucson, AZ wrote its last area forecast discussion before the first event at Aug 31, 10:28 AM MST, 4 hours 42 minutes earlier.
Area Forecast Discussion National Weather Service Tucson AZ 1028 AM MST Tue Aug 31 2021 .SYNOPSIS...The risk for flash flooding remains high today into Wednesday to as deep, tropical moisture filters into the area. Widespread shower and thunderstorm activity is expected. The rest of the week will remain active but become more average in terms of monsoon activity with afternoon showers and storms possible each day. && .DISCUSSION...The overall pattern is defined by a slug of deep tropical moisture moving northward through western Sonora/Gulf of California from the decaying former tropical system (Nora), and a weak upper-low spinning off the northern Baja. Things are still shaping up to be a very busy and wet 24 to 36 hours across all of Southeast Arizona. Sometimes, when we see this type of deep tropical moisture moving north into the area we can almost be too moist and dependent on heating for heavy rainfall, where instead of heavy rain, we see and clearing to quickly cloud over and we see only widespread light showers break out. However, what is different this time, and thus increases our confidence in a heavy rain event, is that the weak upper-low off the coast of the Baja will eject NE through Western AZ over the next 24 hours. As this happens, we will see not only the deep moisture and a weak mid-level disturbance embedded in it moving north into our neck of the woods, but we will also see a more significant mechanism for lifting aloft as can be observed in the H3 omega fields in the diffluent area ahead of this upper feature. This combination is favorable for widespread showers and thunderstorms, with the potential for heavy rain. The most favorable time period appears to be late this afternoon into this evening, with showers with embedded thunderstorms likely persisting overnight into Wednesday morning. Rainfall amounts will generally be 0.50" to 1.50" across the valleys, with 2"-3" inches in the mountains. This moisture remains across the area tomorrow, but will get shunted to the eastern half of the forecast area as drier air is advected in from the southwest. Normally when this type of situation occurs, we can see strong convection develop along the upper moisture discontinuity, which in this case will extend from south-central Pima county into central Graham county. However, given the residual showers and embedded thunderstorms across the region Wednesday morning, there may not be enough instability to support strong updrafts along this boundary. It should be enough though to enhance showers and thunderstorms tomorrow afternoon along this boundary...with it shifting east Wednesday evening. Given all of this, a Flash Flood Watch is in effect for all of Southeast Arizona from 11 AM this morning through 5 AM Thursday morning. && .PREV DISCUSSION...Today and Wednesday. A very interesting pattern will begin to unfold over the next 24-48 hours which we have been keeping a close eye on for the last few days. The moisture influx has already begun as seen on the 31/00z sounding measuring a PWAT of 1.65" up from 1.29" 24 hours prior. PWAT values will continue to rise today as tropical moisture associated with the remnants of what was previously tropical system Nora surge into the area in prevailing southerly flow between a ridge to our east over TX/NM and a closed low spinning off the SoCal coast. Widespread convection is expected to develop today and tonight ahead of the this low as it interacts with the high grade monsoonal moisture in place creating a high flash flood concern. Rainfall totals for the next 48 hours are forecast to be 1"-2" across much of southeast AZ with the higher elevations potentially seeing 2"-4" (locally higher amounts possible). The Flash Flood Watch looks to be in good shape and will remain in place for much of today into late tomorrow night. Initial convection today is expected early this afternoon over Santa Cruz and southern Pima counties before expanding across the remainder of the area late in the afternoon and into tonight. Overnight activity is looking more likely as trough deepens over the Pacific Northwest pulling energy associated with the low off the CA coast northeastward across Arizona. This could last all the way through Wednesday morning as the low passes over the region as an open wave dragging a sfc boundary across the area. The threat of strong to severe storms will be present throughout today and tonight with more organized storms more likely late tonight into Wednesday morning as shear increases, mid/upper levels cool, and moderate instability remains in place. If Wednesday morning is very active, it will be hard to get any substantial activity going for rest of the day with a downward trend in thunderstorms possible throughout the afternoon. High temp for Wednesday remains around 82/83 degrees for Tucson which will challenge the daily record for low maximum temperature which is currently 83 set back in 1967. Thursday through Monday. After tomorrow, active days continue but are expected to come down closer to average. Afternoon and evening showers and storms are expected each day. The ridge will remain centered to our east over the southern Plains through late this week which could open the door to easterly waves transitioning across the area. Ridge begins to shift westward going into the weekend, possibly setting up somewhere around the Four Corners region or Desert Southwest. Temps will warm through late in the week, remaining a few degrees below seasonal normals. && .AVIATION...Valid through 01/18Z. SCT-BKN clouds at 8k-12k ft MSL thru the forecast period. Isold -SHRA will be possible this morning, then SCT-NMRS SHRA/TSRA late this morning through Wednesday midday. The heaviest rainfall appears to be late this afternoon into the evening. Periods of MVFR ceilings/vsbys, mountain obscurations, and wind gusts to 45 kts possible with the stronger storms. SFC wind 12 knots or less, except when influenced by thunderstorm outflows. Aviation not updated for TAF amendments. && .FIRE WEATHER...Expect widespread showers and thunderstorms this afternoon into Wednesday with a threat of heavy rain and flash flooding. Thursday storm chances taper off some with isolated to scattered activity mainly from central Pima County eastward. A more active monsoon pattern then returns this weekend. 20-foot winds will generally be less than 15 mph when not influenced by thunderstorm gusts. Minimum RH values will remain well above critical thresholds this week. && .TWC WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from 11 AM MST this morning through late Wednesday night for AZZ501>515. && Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
More than 1.5 of rain in 3 hours caused the Artesia Wash to flow swiftly and to flood Highway 86 west of Sells.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2021Every state in 2021This day in weather historyWarnings in Arizona, August 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 983569.