A tropical storm that formed off the coast of Mexico on Wednesday is threatening Southern California and its neighbors, a rare forecast that could bring significant rainfall to Los Angeles, San Diego, Las Vegas, and beyond.
Over the next few days, Tropical Storm Hilary is expected to strengthen into a major hurricane as it moves northwest over warm waters toward Mexico’s Baja California peninsula before it weakens and impacts the Southwestern United States, according to a National Hurricane Center (NHC) post.
Though there is a lot of uncertainty in the extended outlook, including the intensity and exact track of the system, the NHC urged people to monitor the forecast and look out for effects such as large swells and strong winds heading into the weekend. The main concern for the Southwestern U.S. now appears to be rainfall.
“Confidence continues to increase on a heavy rainfall and potentially high impact event to [unfold] and focus across parts of the Southwest and California Saturday to Monday associated with a deep lead moisture plume and favorable ingredients in advance of the forecast approach of extratropically transitioning Hurricane Hilary out from the tropical east Pacific,” the National Weather Service said on Wednesday, citing the NHC.
4PM CDT Wednesday, August 16 Key Messages for Tropical Storm #Hilary. https://t.co/BGf3hweIju pic.twitter.com/jcQSEp5YvY
— NHC Eastern Pacific (@NHC_Pacific) August 16, 2023
California, as well as Nevada and Arizona, could get inundated in certain parts with local rainfall amounts varying from 1-4 inches — if not more. As with any forecast, those predicted numbers may change over time.
Tropical Cyclone Hilary will move along the Baja Peninsula this weekend bringing a big increase in moisture and rainfall activity. The heaviest rainfall at this time is expected over southwest AZ and southeast CA, where the greatest flash flood potential will be. #azwx #cawx pic.twitter.com/k4zqybN4pj
— NWS Phoenix (@NWSPhoenix) August 16, 2023
“It’s been a rather sleepy monsoon season, but that could change this weekend as tropical activity spices things up,” said the National Weather Service branch for Las Vegas. “There remains *a lot* of uncertainty in the details, but the ingredients are coming together for a wet weekend in the area. Stay tuned!”
It's been a rather sleepy monsoon season, but that could change this weekend as tropical activity spices things up. There remains *a lot* of uncertainty in the details, but the ingredients are coming together for a wet weekend in the area. Stay tuned! #nvwx #cawx #azwx pic.twitter.com/TqyiDz2m4T
— NWS Las Vegas (@NWSVegas) August 16, 2023
As explained in a Weather Underground post from last year, tropical cyclones hitting California are a rare weather phenomenon because of unfavorable conditions in the area such as cooler water and high pressure, though the state has been more commonly impacted by the remnants of such storms.
A couple systems that were tropical storm strength have rolled into Southern California over land in recent decades, but the only time on record that one made landfall there dates back to the 1930s.
“Pattern movement allows #Hilary and it’s moisture to come north towards Southern California Sunday and Monday,” Weather Channel meteorologist Jim Cantore said in a post to X. “1939 was the last tropical storm landfall so we don’t have a lot to gauge this on, but we know any high rate events like a tropical system pose a threat for FLASH FLOODING especially over burn scars and steep terrain.”