Tropical Storm Hilary, the first tropical storm to impact Southern California in 84 years, brought heavy rain and significant flooding to Ventura and Los Angeles counties. 50 to 5 inches of rainfall.
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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 LOX wrote it up.
Tropical Storm Hilary, the first tropical storm to impact Southern California in 84 years, brought heavy rain and significant flooding to Ventura and Los Angeles counties. Rainfall totals were very impressive with mountain areas receiving 3 to 9 inches of rainfall while coastal and valley areas received 2.50 to 5 inches of rainfall. Rainfall rates were also very impressive with rates around 1 inch in less than an hour reported at times. With such heavy rainfall, numerous reports of flash flooding as well as mud and debris flows were received. As for winds, most areas reported gusts in the 30 to 50 MPH with local gusts in excess of 80 MPH in some mountains locations in Los Angeles county.
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 Los Angeles, CA wrote its last area forecast discussion before the first event at Aug 20, 4:49 AM PST, 2 hours 51 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 549 AM PDT Sun Aug 20 2023 .SYNOPSIS...20/237 AM. Showers and thunderstorms will spread into Los Angeles County this morning. Later today widespread rain and scattered thunderstorms will increase as Hurricane Hilary approaches. The peak of this dangerous storm will be from late this afternoon through the pre dawn hours Monday Morning. Significant flooding and wind threats exist, especially over Los Angeles and Ventura Counties. Rain will decrease during the day on Monday. More typical conditions will return on Tuesday, with a chance of afternoon thunderstorms in the mountains. && .SHORT TERM (TDY-TUE)...20/549 AM. ...TROPICAL STORM WARNING WITH A THREAT OF DANGEROUS FLOODING AND STRONG WINDS FOR MUCH OF LOS ANGELES AND VENTURA COUNTIES, WILL OCCUR LATER THIS AFTERNOON AND OVERNIGHT INTO EARLY MONDAY MORNING... Please visit the National Hurricane Center's web page: www.nhc.noaa.gov/refresh/graphics_ep4+shtml/061248.shtml?cone#contents For the latest position and forecast track of Hurricane (soon to become Tropical Storm) Hilary. For further information on Hilary and its impacts on southwestern CA please see the latest Hurricane Local Statement (LAXHLSLOX). There is good confidence in the track of Hilary as most all ensembles from multiple mdls show little deviation from each other. Unfortunately even a 25 mile departure from this forecast track will have major implications for the forecast esp VTA county. A track to the west will be much wetter and windier while a more eastward track would bring less rain and wind. It is strongly advised that people keep a close eye on the movement of this system. Hilary is beginning to accelerate and now its major effects will occur a little earlier than Saturday's Thinking. The peak of the storm will likely occur between 4pm today and 4am Monday. This is a major and very dangerous storm with rainfall and flooding the preeminent threat. This is especially true for the LA/VTA county mtns and the Antelope Valley, where significant and dangerous flash flooding is the most likely due to orographically enhanced heavy rain on the north slopes of the eastern San Gabriel mtns. Rainfall total estimates have not changed. Record amounts of rainfall will be likely as optimal synoptic forcing interacts with deep tropical moisture (peak PWATs near 2.50 inches) Forecasted rainfall through Monday is 1.5-3 inches for most coastal/valley areas in LA/Ventura counties, with 3 to 7 inches possible in the LA county mountains and Antelope Valley. For Santa Barbara and San Luis Obispo counties, estimated rainfall projections are expected to range between 0.1 and 0.50 inches, except 1-2 inches possible in the mountains and interior. Peak rainfall rates are generally expected range between 0.50 and 1.00 inches per hour, but over the north facing slopes where strong upslope enhancement is likely rates up to 1.5 inches per hour are possible. Citizens need to be aware that this system will bring life threatening flooding of small streams, creeks, arroyos, and ditches. Large debris flows will be possible along with the threat of rock and mudslides. Significant roadway flooding is likely. Hilary will bring strong and gusty winds to the area There is now high confidence that heavy rain and gusty winds to tropical storm force (40-50 mph with gusts over 60 mph possible in the mtns) will affect the Warning area. Because the wind direction is the same as a Santa Ana wind event, the areas typically affected by northeast offshore winds will be most vulnerable. The strong winds will have the potential to bring downed trees and power lines as well as power outages. The system is now expected to move out pretty quickly after dawn on Monday leaving clearing skies and a residual threat of TSTMs across the interior. Winds will subside quickly as well. Max temps will mostly be in the mid 70s to mid 80s or about 6 to 12 degrees blo normals. Long wave troffing will cover the west coast on Tuesday. Skies will be partly cloudy at worst. There may be some build ups in the afternoon over the mtns but there is not enough moisture to produce a threat of TSTMs. Lots of sunshine and drier air will allow for 4 to 8 degree warm up over most of the area. .LONG TERM (WED-SAT)...20/324 AM. The GFS and EC deterministic as well as the GEFS and EPS ensembles are all in good agreement for the xtnd forecast. And all in all it will be 4 days of benign weather. A large upper high will expand and push into the state from the east on Wed and Thu. Then on Friday another long wave trof pushed in from the west and lower hgts. The marine layer will slowly reestablish itself and there will be areas of night through morning low clouds and fog across the coasts (hgts will be high enough to prevent the clouds from getting into the vlys) Max temps rise on Wednesday but then only change a few degrees up or down each day Fri thru Sat. Max temps will remain below normals through the period. && .AVIATION...20/1206Z. At 12Z at KLAX, There was no marine layer. There was a sfc based inversion with a top of 2300 and a temps of 24 C. Low confidence in TAFs, especially after 18Z. Rain and isolated to scattered thunderstorms will build into the region through 18-00Z, with periods of heavy rain focused between 20Z and 03Z focused across LA County, possibly extending into Ventura County TAFs. An abrupt wind shift is likely sometime between 22Z and 06Z as Tropical Storm passes just east of the area. Low confidence in potential shower timing and intensity along the periphery of the storm for TAFs KSBA and north. KLAX...Fairly good confidence in TAF through 16Z then moderate confidence. Cig, vis, wind speed and direction will likely change frequently as TS Hilary moves by. Moderate confidence that there will be an extended period of an east wind component greater than 8 kt from 16Z to 22Z. Less confidence in the cross wind fcst in the afternoon which has a 30 percent chc of not developing. KBUR....Fairly good confidence in TAF through 16Z then moderate confidence. Cig, vis, wind speed and direction will likely change frequently as TS Hilary moves by. Fair confidence that Cig/Vis will be predominately MVFR through at least 00Z. && .MARINE...20/351 AM. High confidence in deteriorating conditions focused south of Point Conception this afternoon and evening with gradual improvement tonight and especially into Monday. A Tropical Storm Warning continues south of a line from the Channel Islands to Point Mugu where there is a 40-70 percent chance of gusts in excess of 40 kts, most likely along and south of a line from Long Beach to San Nicolas Island. A Small Craft Advisory has been issued for all other waters, in effect from this afternoon into this evening. Only moderate confidence on timing and coverage and may need to be adjusted depending on Hilary's eventual track. Isolated to scattered thunderstorms today into tonight, focused across southern waters could support frequent lightning, gusty winds and steep choppy seas, and a waterspout. Marine interests in the southern California waters are urged to continue monitoring the latest information from the National Weather Service. && .BEACHES...20/348 AM. Hurricane (soon to be tropical storm) Hilary will continue to move in a northerly direction off the Baja coast early this morning while weakening. This system will bring a long-period southeasterly swell across the coastal waters which will generate elevated to high surf today and Monday. There is a 50 percent chance that surf conditions could reach high surf advisory levels. Along with the surf, strong and dangerous rip currents are expected. Additionally, the southeast swell may generate hazardous conditions at east and southeast facing harbor entrances. && PUBLIC...Rorke AVIATION...Munroe MARINE...Munroe BEACHES...30 SYNOPSIS...RK weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox
The Los Angeles radar (KVTX), 63 km away, was scanning. The volume nearest the first event began at 15:41 UTC.
32 flash flood, 1 funnel cloud. Local standard time, as filed.
Heavy rain generated flash flooding near the community of Santa Clarita. Significant flooding closed the truck bypass lanes on Interstate 5 and Highway 14.
Heavy rain generated flash flooding near the community of El Monte. Significant flooding impacted Interstate 10, stranding numerous vehicles.
Heavy rain generated flash flooding near the community of Valencia. Significant flooding was reported on Interstate 5 near Magic Mountain Parkway.
Heavy rain generated flash flooding in the community of Sherman Oaks. On Interstate 405, numerous vehicles were stranded on the flooded roadway.
Heavy rain generated flash flooding near the community of Castaic. Significant flooding was reported on the Old Road at Hillcrest Parkway.
Heavy rain generated flash flooding in the community of Culver City. On Interstate 10, numerous vehicles were stranded in the flooded roadway. Also, small streams overflowed their banks, flooding several backyards.
Heavy rain generated flash flooding in the community of San Fernando. On Interstate 405, numerous vehicles were stranded in the flooded roadway.
Heavy rain generated flash flooding in the community of Moorpark. On Moorpark Road, significant mud and debris flows were reported.
Heavy rain generated flash flooding in the community of Palmdale. At the intersection of Highway 114 and Avenue S, significant debris flows were reported.
Heavy rain generated flash flooding near the community of Diamond Bar. Significant flooding was reported on Highway 57.
Heavy rain generated flash flooding near the community of Fillmore. Significant flooding was reported on Highway 126.
Heavy rain generated flash flooding near the community of Newbury Park. Significant flooding was reported on Highway 101 near Ventu Park Road.
Heavy rain generated flash flooding near the community of Somis. Significant flooding was reported on Highway 118, near Aggen Road.
Heavy rain generated flash flooding near the community of Lake Los Angeles. Significant flooding was reported on Avenue P-8.
Heavy rain generated flash flooding near the community of Quartz Hill. Significant flooding was reported on Highway 14 near Avenue M.
Heavy rain generated flash flooding near the community of Camarillo. Several vehicles were stuck in mud near the intersection of Trueno Road and Center School Road.
Heavy rain generated flash flooding near the community of Lake Hughes. Several cars were stuck in mud on Pine Canyon Road.
Heavy rain generated flash flooding near the community of Burbank. Northbound lanes of Highway 170 were flooded.
Near the community of Fillmore, the swift water rescue team initiated several rescues from the Santa Clara River.
Heavy rain generated flash flooding near the community of Palmdale. Several parked vehicles were completely submerged in water.
Heavy rain generated flash flooding near the community of Ojai. Numerous rocks were reported across Highway 33.
Heavy rain generated flash flooding near the community of Castaic. Significant flooding was reported on Interstate 5 near Halsey Canyon Road.
Heavy rain generated flash flooding near the community of Burbank. Several vehicles were stuck in flood waters on Interstate 5 near Lankershim Boulevard.
Near the community of Saticoy, the swift water rescue team initiated several rescues from the Santa Clara River.
Heavy rain generated flash flooding near Point Mugu Naval Base. On Highway 1, several rocks fell on a vehicle.
Near the community of Palmdale, several homes reported significant flood damage.
Heavy rain generated flash flooding near the community of Westlake Village. Significant flooding was reported on the Westlake Boulevard onramp on Highway 101.
Heavy rain produced flash flooding near the community of Agoura Hills. At the intersection of Highway 101 and Kanan Road, several vehicles were stuck in flood waters.
Near the community of San Fernando, five feet of mud covered several lanes of Interstate 5.
Near the community of Azusa, a couple feet of mud covered the lanes of Highway 39.
Near the community of Alhambra, flooding was reported at the connector of Interstate 10 and Interstate 710.
Mud and debris flows were reported on Piuma Road near Malibu Canyon Road.
A funnel cloud was observed west of the community of Cuyama.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, August 2023
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: 1136159, 1136161, 1136166, 1136152, 1136164, 1136148, 1136146, 1136151, 1136156, 1136163, 1136165, 1136168, 1136170, 1136171, 1136172, 1136175, 1136176, 1136177, 1138222, 1136180, 1136179, 1136181, 1136183, 1138223, 1136185, 1138227, 1136186, 1138221, 1138224, 1138226, 1138228, 1138229, 1138231.