August 18, 2023 at 7:51 am

FINAL FORECAST: Tropical Storm Hilary Will Hit Southern California and Vegas Starting This Weekend; Details and Maps

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Major Hurricane Hilary will hit Southern California as a Tropical Storm starting tomorrow (Saturday) east of Los Angeles and then affecting everyone equally with Sunday into Monday morning being the main part so read on for details along with me upgrading the Low Desert, including the Coachella Valley from Extreme into the rare Emergency Risk per the Southern California Weather Force Risk Assessment Model.  Please note that although this is a long forecast, the details are to be read word for word as locations will matter.

Hurricane Hilary is a category four system.  This system has finally made the northwest turn and will solidify hitting Southern California and Las Vegas head on.  The confidence has been extremely high for this to happen due to the left over upper-level low of Eugene, which affected us well over a week ago.  This upper-level low retrograded west of Vandenberg and is the one fully responsible for pulling and maintaining a south to north flow from the tropics to the Desert Southwest.

THUNDERSTORMS:  Storm activity will start in the low deserts (Imperial/Desert Center/Needles/Las Vegas as early as today.  Increasing tropical moisture will move into the areas west of Los Angeles’ latitude on Saturday.  This will bring some instability with it, so I do think we have the chance of thunderstorms ahead of the main system from the Inland Empire, High/Low Desert, and San Bernardino, Riverside, and San Diego County Mountains.  I will consider updating everyone on those thunderstorms I expect with a Thunderstorm Watch, which will label the focus areas when the time comes.  You can expect that this this evening (Friday) but here is a map on the thunderstorm zones for today and tomorrow.


As Sunday rolls around, more tropical moisture will be introduced along with upper-level divergence on the north side of Hilary’s broad circulation.  This is when Los Angeles, Ventura, Santa Barbara, San Luis Obispo, and Kern County see the swath of precipitation, lasting into Sunday night, and moving out over the day on Monday.

Now, understand something.  This system will have what I call whiners of weather forecasts where you will be in a dryslot on Saturday and wonder “Where the heck is this system?”  You will say that only to understand that the main event for the majority of the Southern California Metro Population Zones will be Sunday into Monday.

Because of the prolonged rainfall across the Low Deserts, the upgrade via the Southern California Weather Force Risk Assessment Model is at Emergency Risk, the dark blue shade on the article image within this write-up.

Use the zoom-in images below for your sector of Southern California to know what rainfall amount is forecast.  Remember, this is in a short period of time, and anything in the magenta or dark blue would be considered a major flood and erosion event, especially in the local mountains and all desert zones where I think the Coachella Valley will see anywhere from 7 to 10″ of rain.

Master General Meteorologist – Raiden Storm

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