An area of high pressure centered over the northern Baja Peninsula allowed for temperatures to climb nearly 10 degrees above seasonal normals. Two direct heat fatalities were reported by the Maricopa County Department of Public Health.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 PSR wrote it up.
An area of high pressure centered over the northern Baja Peninsula allowed for temperatures to climb nearly 10 degrees above seasonal normals. Two direct heat fatalities were reported by the Maricopa County Department of Public Health.
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 Phoenix, AZ wrote its last area forecast discussion before the first event at Sep 27, 3:10 AM MST, 6 hours 50 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 310 AM MST Thu Sep 27 2018 .SYNOPSIS... Warm and overall dry conditions will last into the weekend as temperatures continue to run well above average each day. A Pacific low pressure system and remnants from a tropical cyclone will bring widespread rain chances across the Desert Southwest early next week while significantly lowering temperatures. && .DISCUSSION... For the next few days, the weather pattern over the desert southwest will be very quiet; the only issue will be the continued hot temperatures reaching nearly 10 degrees above seasonal normals under sunny skies. After that, BIG changes are coming as TS Rosa moves into the state. But before we get into that... Currently high pressure aloft remains situated over the desert southwest with 500mb heights around 590dm per the latest plot data. Dry northwest flow aloft is in place across the area and the 1 am surface dewpoints were running mostly in the 40s. IR imagery showed generally clear skies area-wide. Model guidance remains consistent that the ridge will continue to build slightly today and then shift east Friday with 500mb heights peaking around 592dm. This will result in two more hot days, with Phoenix reaching around 105 each day and hottest western deserts climbing to around 107. Normal high in Phoenix is now 96 so highs will be nearly 10 degrees above normal; despite the hot conditions heat risk guidance keeps most of the deserts in the moderate risk of excessive heat category so we will not be issuing an excessive heat watch at this time. Messaging the continued early fall heat will be our approach. Slightly cooler conditions are expected Saturday as the high begins to weaken; look for highs around 101 in Phoenix. Saturday may well be the last day we see triple digits in Phoenix as much cooler conditions will be developing Sunday into next week as moisture from hurricane Rosa moves into the area. Starting on Sunday, we can expect a major pattern shift as the high pressure system over the desert southwest weakens and starts moving off to the east while a deep upper trof moves into position off the California coast. As this occurs, hurricane Rosa, currently well to the southwest off the tip of Baja California, moves north off Baja and then takes a sharp right turn and begins to head for Arizona. Tropical moisture and thick cloud cover will begin to spread north and into Arizona Sunday and light showers will begin to develop during the day, although dynamics will still be rather weak. At this point there is excellent consistency between pretty much all operational models as well as the various ensembles with regard to the main forecast narrative - a major precipitation event with potential flooding over Arizona - looks to be a VERY good bet for sometime early next week, probably in the Monday night thru Tuesday night time frame. Most of the experimental hurricane tracks from ESRL track TS Rosa northeast and into Arizona early next week with the center moving through somewhere between Phoenix and Yuma. GEFS plumes data suggests rainfall in Phoenix between 1 and 4 inches in Phoenix with this event, with similar amounts forecast over the western deserts including Yuma. WPC rainfall estimates suggest storm total precip in PHoenix around 2 inches. At this time it appears that it's not so much a matter of "will it rain" but "how much will it rain" and "exactly when will the heaviest rain fall". The biggest issue at this time is timing; the current GFS is much faster bringing the remnants of Rosa into Arizona - it pushes the main wave thru the Phoenix area by 12z Tuesday. The operational ECMWF is much slower; at 12Z Tuesday it keeps Rosa's remnants off the northern Baja coast and eventually moves it into central Arizona during the day on Tuesday. Similar timing issues exist with the various ensemble systems such as GEFS ensemble members. So, for now we cannot really pinpoint the 6 hour period of heaviest rainfall with Rosa and we will simply be showing increasing POP trends starting Monday and continuing through Tuesday night. Right now we feel the GFS is likely too fast, while the ECMWF is a bit slow. We will base our timing on a blend between the two, with highest POPs over the lower central deserts running around the 06z to 18z period on Tuesday. Forecast storm total QPF in Phoenix is running near 2 inches. Current MRA MOS numbers focus on the Monday night period, and have 100 percent readings for many of our stations. There are a couple of issues that will help to increase rain chances as well as rain totals. First is the presence of the deep trof just to our west. Of course there will be considerable dynamics associated with the system; strong QG forcing as well as being in a favorable right-read quadrant of a strong upper jet. Strong low level southerly flow ahead of Rosa will bring orographics into the mix, espect rain totals to be enhanced in the favored upslope areas north and east of Phoenix especially Monday night into Tuesday. We don't really expect wind to be a major issue with Rosa but breezy to windy conditions are a good bet as Rosa's remnants move through the area. Also, instability does not look to be excessive so we will limit thunderstorm wording to just slight chances; for example "showers likely with a slight chance for thunderstorms". Most likely the POPs will continue to climb and by later this weekend we will probably have categorical numbers approaching 100 percent for a good chunk of the CWA, for at least one 6 hour forecast period. Given the heavy rain forecast, flooding will likely be a concern; at this time it is too early and there is too much uncertainty to merit issuing a flash flood watch but we will likely have to issue one as the event grows closer. Finally, we can expect MUCH cooler high temperatures early next week; Phoenix should drop into the upper 80s to around 90 next MOnday and Tuesday with little change thru midweek. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL; Southeast California/Southwest Arizona including KIPL and KBLH: High pressure and a dry airmass to keep skies mainly CLR through the TAF period. Light diurnal winds under 10 kt can be expected at all TAF sites, with no aviation weather concerns expected. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Saturday through Wednesday: Temperatures will begin the weekend a few degrees above normal before a dramatic cooldown amidst a significant pattern change. The remnants of Hurricane Rosa will move into the Southwest early next week, prompting a substantial increase in moisture. Scattered showers and thunderstorms may develop as early as Sunday afternoon, becoming more widespread Monday and Tuesday. Many areas may receive over one inch of rainfall. Humidities will also increase, bottoming out near 40 percent both on Monday and Tuesday. The increase in humidity and rainfall potential should alleviate any short-term rainfall concerns by early next week. Winds will generally remain less than 10 kt throughout the period, outside of typical diurnal wind gusts on Saturday and Sunday. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...CB AVIATION...Percha/Rogers FIRE WEATHER...Rogers
The national radar mosaic for the moment the first event began.
2 heat. Local standard time, as filed.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Heat, Central Phoenix | 2018-09-27 | Unknown | Direct | ||
| Heat, East Valley | 2018-09-27 | Unknown | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, September 2018
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: 867319, 867320.