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Hilary: NWS Got ‘Hurricane Capable’ in SoCal Just in Time

“Unusual would be an understatement,” said Los Angeles County Meteorologist John Dumas. “Obviously there’s no correlation between the earthquake and the storm, but just the odds of one and then the other are pretty out there.”

August 20,2023: A high Los Angeles River rushes under Sepulveda Boulevard during remnants of Hurricane Hilary.
Shutterstock/Sam the Leigh
What’s amazing about the recent hurricane in Southern California is that it was the first time the area had a tropical system hit since 1939. The rainfall amounts too were staggering, but luckily the wind wasn’t much more than a typical Santa Ana wind the area sees. Oh, and don’t forget the magnitude 5.1 earthquake that competed with Hilary for people’s attention.

Also, as luck would have it, the National Weather Service (NWS) had in June just deployed its new Hurricane Analysis and Forecast System (HAFS) in Los Angeles and San Diego counties.

“Unusual would be an understatement,” said Los Angeles County NWS Meteorologist John Dumas. “Obviously there’s no correlation between the earthquake and the storm, but just the odds of one and then the other are pretty out there.”

He added that, “just by pure luck this year the Weather Service made the San Diego office and the Los Angeles office fully hurricane capable.”

Without the new system, it would have been an extremely arduous task to synthesize all the information that goes into forecasting what a storm like Hilary will do and thus difficult to inform local emergency managers and media of what to expect and how to prepare people.

So what it means is that Los Angeles and San Diego, for the first time, had the tools that are used to forecast hurricanes in the Gulf and the Atlantic, which gave them the ability to issue a hurricane warning. “How fortunate were we that for something this rare we had gotten through all the ‘buttonology’ and talked about this just two months ago.”

There are many pieces of information that go into producing a hurricane forecast, including the rain forecast, which comes from a center in Maryland; the wind forecast, which is based on a model sent by the hurricane itself; and the storm surge unit that comes from the National Hurricane Center. All of that is entered into the computer.

“Then we run through the procedures that originally had only been coded for East Coast or Gulf Coast, so there was a lot of work to make sure things would work out on the West Coast,” Dumas said. “It’s extremely complicated.”

One of the biggest impacts — maybe the biggest — is the storm surge, at least on the East Coast. The system, given the direction of the storm and its strength, will show where there may be “sea water surge flooding.”

“To be able to share that kind of thing with the staff ahead of time, so that when we saw this was coming we could look at those models and then communicate with our emergency manager partners, especially on the marine side and say, ‘Expect things in this area or maybe up to this height,”’ Dumas said.

Another bit of luck, perhaps, was that emergency managers already knew where to expect flooding after this past winter’s heavy rainfall, and so they were able to respond accordingly. For example, helicopters were flown over some of the dry riverbeds where homeless people congregate, and warnings were announced to be aware of flooding or to evacuate.

“The National Weather Service is pretty good about that 72-hour mark with their confidence, and so early last week when we were tracking we had a few calls and then we said, ‘Okay, it’s time for coordination calls with our county departments and city departments and special districts,’” said Emily Montanez, director of communications for the Los Angeles County Office of Emergency Management.

The county issued its Wireless Emergency Alerts, which accompanied the NWS flash flood warnings. The county also issued evacuation warnings to people on Catalina Island and to areas in the North County.

Even with heavy rainfall in some areas, the preparation and response from residents was welcome.

“I think we have to look back at our most recent winter, [which had] record rainfall,” Montanez said. “It felt like one of the days we experienced in January and February.”