On August 18, 2023, Hurricane Hilary, a powerful Category 4 storm with winds of 130 mph, was heading…

On August 18, 2023, Hurricane Hilary, a powerful Category 4 storm with winds of 130 mph, was heading towards Southern California and the Southwest U.S. This storm, although expected to weaken as it moves north, had the potential to become the third-ever tropical system to make landfall in California.[0] The last time a tropical storm made landfall in California was in 1939, and it could remain a tropical depression as far north as Oregon.[1]

According to current models, Hilary was expected to weaken to a Category 1 hurricane before making landfall in Baja California, Mexico.[2] By the time it reached San Diego County on Sunday or Monday, it would likely be a powerful tropical storm.[3] The National Weather Service predicted that Hilary would track northwest and then north, potentially making landfall as a tropical storm somewhere between Los Angeles and just east of San Diego, or it could come ashore in Baja California before entering Southern California.[4]

The National Weather Service Weather Prediction Center issued a “high” risk outlook for excessive rainfall leading to flash flooding in parts of Southern California. This included the far Southern California desert, where three to six inches of rain was expected, with isolated higher amounts of up to 10 inches in mountainous areas.[4] The forecast warned of 1-in-100-year rainfall amounts, with the potential for 3-inch amounts in an hour.[4] Some guidance even showed local amounts of 7 inches or more, which would be extremely rare for the region from a tropical cyclone.[4]

Flood watches were already in effect for southwestern Arizona and southeastern California from Saturday morning through Monday morning.[5] The NWS also issued flood watches for Los Angeles County, Orange County, Ventura County, and Mojave National Preserve. These areas were at risk of excessive runoff and flooding in rivers, creeks, streams, and low-lying locations.

In response to Hurricane Hilary, Joshua Tree National Park and Mojave National Preserve announced that they would be fully closed to visitors.[6] The park closures were due to concerns about potential debris flow and flooding.

While tropical storms are rare in Southern California, they are not unheard of.[7] The region is protected by relatively cool ocean waters, making it unlikely for hurricanes to make landfall.[8] However, climate change may make these storms more frequent in the future.[3]

Drivers were advised to never drive through a flooded roadway if they could not see the pavement.[9] Even a few inches of water running at the right velocity could sweep a car off the road.[9] Residents in unincorporated areas were provided with free bags and sand at fire stations to help protect their properties from flooding.

Hilary's showers were also expected to raise winds across large parts of the Bay Area and Central Coast.[10] Although the winds over the ocean surface were expected to be at tropical storm force, winds over land blowing downslope through the mountains could reach hurricane strength.

Overall, Hurricane Hilary posed a significant threat to Southern California and the Southwest U.S., with heavy rainfall and the potential for flash flooding. Residents and authorities were urged to take precautions and stay updated on the latest weather forecasts and warnings.

0. “Hurricane Hilary could bring flooding, high winds to California” The Washington Post, 18 Aug. 2023, https://www.washingtonpost.com/weather/2023/08/18/hurricane-hilary-southern-california-rain-forecast/

1. “Hurricane Hilary could bring heavy rain, powerful winds locally” VC Star, 18 Aug. 2023, https://www.vcstar.com/story/news/2023/08/18/hurricane-hilary-could-bring-heavy-rain-powerful-winds-locally/70614820007/

2. “Airlines Issue Travel Waivers Ahead of Hurricane Hilary” TravelPulse, 18 Aug. 2023, https://www.travelpulse.com/news/impacting-travel/airlines-issue-travel-waivers-ahead-of-hurricane-hilary

3. “When was the last time a hurricane hit San Diego County?” NBC San Diego, 19 Aug. 2023, https://www.nbcsandiego.com/news/local/when-was-the-last-time-a-hurricane-hit-san-diego-county/3287670

4. “California's first Tropical Storm Watch on record as Hurricane Hilary heads for Baja » Yale Climate Connections” Yale Climate Connections, 18 Aug. 2023, https://yaleclimateconnections.org/2023/08/californias-first-tropical-storm-watch-on-record-as-hurricane-hilary-heads-for-baja

5. “Hurricane Hilary updates: Live coverage as storm hits AZ, CA” The Arizona Republic, 19 Aug. 2023, https://www.azcentral.com/story/news/local/arizona-weather/2023/08/18/hurricane-hilary-rain-storm-updates-arizona/70623192007/

6. “Hurricane Hilary live updates: How the Palm Springs area is preparing” Desert Sun, 18 Aug. 2023, https://www.desertsun.com/story/weather/2023/08/18/palm-springs-area-under-tropical-storm-watch-as-hurricane-hilary-nears/70620451007/

7. “KABC’s Dallas Raines on How Hurricane Hilary Could Bring Floods, Even Tornadoes to Southern California” Variety, 19 Aug. 2023, https://variety.com/2023/tv/news/hurricane-hilary-dallas-raines-floods-tornadoes-impact-southern-california-1235700233/

8. “Hurricane Hilary could bring rainfall and cooler temps to the Valley” Axios, 18 Aug. 2023, https://www.axios.com/local/phoenix/2023/08/18/hurricane-hilary-phoenix-arizona-rain-cool-temperatures

9. “Storm Coming: Driving Tips and Where to Get Sandbags” countynewscenter.com, 17 Aug. 2023, https://www.countynewscenter.com/storm-coming-driving-tips-and-where-to-get-sandbags

10. “How Hurricane Hilary could impact the Bay Area this weekend” San Francisco Chronicle, 18 Aug. 2023, https://www.sfchronicle.com/weather-forecast/article/bay-area-hurricane-hilary-18300696.php

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