Hilary And Rain In Southern California

August 20, 2023

Overcast and humid this near-noon Sunday here in California’s Central Valley — we’re awaiting the impact from former Hurricane Hillary, now categorized a tropical storm, in the maybe form of rain and wind. Although the biggest Hilary splash will be south and east of us (southern Cal, and Nevada), there’s an unknown mystery to all our weather nowadays due to excessive heating and easy shit might turn out to be a horrible, nasty turd.
Climate change creates chaos —  understand the reality.

Under the cloud layer already, however:

Despite supposedly it ‘never rains in Southern California,’ it’s raining in southern California — except it’s less than anticipated. From the LA Times a short while ago:

Hilary may be coming in a little faster than initially expected. Tropical-storm-force winds — sustained winds of at least 39 mph — were forecast to arrive in San Diego County as early as Sunday morning.

Across Southern California, officials are particularly concerned about Sunday afternoon and evening.

Hilary’s track has shifted slightly eastward. The risk for coastal flooding in L.A. County has perhaps dropped, but flooding risks inland still remain significant, and especially dangerous in the deserts and mountains.


Hilary is a big storm, roughly the size of the state of Arizona. As expected, on Sunday morning, Hilary weakened from a hurricane to a tropical storm, but still had powerful maximum sustained winds of 70 mph and still represented a significant flooding threat.

Rain and flooding is the biggest risk from Hilary, with particular risk in the deserts and mountains. Already, roads have turned into rivers in Baja California, forecasters said, and the storm is expected to have similar impacts in some places here.


Some rain rates could exceed one inch per hour, even up to 1.5 inches per hour. A couple of projections show up to 2 inches per hour, forecasters said. Rain rates of 1.5 inches per hour is torrential rain, which can result in catastrophic flooding over a desert, mountain or valley.

A year ago, Death Valley saw 1.7 inches of rain during “unprecedented rains” — what was the rainiest day on record — causing major floods and forcing the closure of all roads in the park, according to the National Park Service.

Some desert areas in Southern California could see a year’s worth of rain in as little as a 24-hour period. The rain won’t be constant, but could involve several rounds of heavy rainfall.

And even strange as it might seem, a little twister material, too:

Another brick-in-the-wall for climate change:

Via Inside Climate News yesterday:

But a lack of research and data about the rare tropical cyclones in the region will leave many continuing to wonder about how often they’ll face such storms as the Eastern Pacific warms.

National Weather Service forecasters on Friday issued the first-ever tropical storm watch for Southern California, and said the “serious and unusual situation” includes the threat of a tropical cyclone moving up into Southern California on Sunday and Monday, with widespread flooding possible and the potential for tropical storm-force wind gusts above 50 mph. National Hurricane Center forecasters anticipated that Hilary’s winds could be at 100 mph as it approaches the Southern California coast.

“I’m watching very carefully to see what track it’ll take, because the information we have so far is, there will be impacts,” said Kim Wood, an atmospheric scientist at the University of Arizona who studies tropical cyclones in the East Pacific. “It’s still uncertain if the impacts will be from a direct hit or if the storm center will stay offshore.” Either way, she added, the system will bring wind and a big surge of moisture to the deserts of southern California, Nevada and Arizona.

“Hilary is already really big, and storms don’t tend to shrink quickly once they get to that size,” she said. “If it undergoes something called an eyewall replacement cycle, it might get weaker, but it’ll get bigger. And the bigger it gets, the more likely it is to maintain its structure.” That means even when it moves over cooler water near California, the storm is still likely to reach farther inland, she added. The storm, however, will weaken to below hurricane strength before making landfall, likely as a tropical storm, she said.

East Pacific hurricanes generally form off the coast of Mexico and often head west, away from land, losing strength as they curve northward over cooler water. But depending on seasonal weather patterns, some curve back toward the east, making often-damaging landfalls along the west coast of Mexico.

But having a major hurricane barreling due north toward California is exceedingly rare, and the tropical storm watch issued for Southern California, is a “historic first for CA,” climate scientist Daniel Swain posted on social media, adding that rainfall amounts in the deserts of southeastern California could be equally historic, with one to two years worth of rain falling in the next few days. Rainfall of 3 to 6 inches, and up to 10 inches in spots, is expected across portions of southern California and southern Nevada, “which would lead to significant and rare impacts,” according to the National Weather Service.


One thing that may increase the risk is the steady rise of sea surface temperatures. For now, the ocean off the coast of Southern California is often below 79 degrees Fahrenheit, which is the minimum needed to sustain a tropical system. But, as in other areas, the ocean in the region is heating up quickly, and if it starts to stay above that temperature, it could drive storms longer on a northward track.

“If we look at the last 60 years or so, the trend is definitely positive,” Wood said of the increasing water temperatures in the region. “We’re looking at a half-degree Fahrenheit every 10 years. We still have that quick change in sea surface temperatures in that area, but sea surface temperatures are going up, and there’s kind of an impressive blob of warming right off the coast of Baja California.”

And to finish this essay on Hilary of the future against history’s hype:

Tornado, flooding, or both, so once again here we are…

(Illustration out front: ‘The Blue Umbrella,” (1914), color woodcut on paper, by Helen Hyde, and found here.)


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