Hurricane ROSA is a category four system and will weaken back to category three by the evening.  Latest satellite images show an impressive system and it is still expected into the Southwest USA after the weekend with ‘pending’ Pacific Storm Ophelia joining the show.  Read on for details.

First I will say that an increase in onshore flow this evening into tomorrow (Saturday morning) will bring widespread light rain or drizzle along the coast and somewhat inland in all areas of the forecast area.  This will also affect the viewing at times of the Miramar Air Show, as previously stated.  I do not need a short term forecast ‘alert product’ for this so this paragraph will serve as the forecast.

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The Southern California Weather Force Flood Watch (link) remains in place, issued yesterday for the eastern low deserts.  Hurricane ROSA will move into the region as a tropical storm by October 1st. Rainfall will begin out ahead of it later on Sunday the 30th in the watch area.

The increased rainfall through the 1st will bring flooding conditions in the watch area, with the CO River Valley seeing 3-5+” in a short period of time.

Imperial Valley may see 1-2″. Driving on back roads and highways is NOT recommended during the watch period.Be very advised that this is a dangerous situation and must not be taken lightly.

Premium members can check the zoom-able map to see where you reside in getting the most or least rainfall from this event by looking below.

There is a chance that I could issue the rare Tropical Storm Watch for the area when I figure out the final track the system will take.  If it goes more west than projected than I’ll have to monitor a tropical storm watch chance further west than Imperial County.  Right now I’ll keep it through Imperial County to the CO River Valley for such an alert product.

ROSA will move into the United States on Monday into Tuesday.  Really not much change from the previous article where we do have a split in dynamics with merging weather systems.  The cutoff to the west of California and ROSA in our eastern forecast area.

Rainfall Trends in the member section has been trending 85% chance of rainfall in Los Angeles (center point of records) for a good clip so confidence in rainfall is high.

The cutoff’s track will determine who gets thunderstorms with it.  Forecast a couple days ago did show the areas west of Los Angeles being at the center and this looks probable even today.  Areas in the SLO/SBA County areas surrounding Vandenberg Air Force Base are in the upper divergent section of the diving cutoff system.  Cutoffs can change trajectory so this is continuing to be watched.

Offshore flow for rising temperatures and the monitoring of the first Santa Ana Winds of the season will be by the end of this next week followed by monitoring of what will become Hurricane SERGIO forming just as ROSA makes landfall in the forecast area.  SERGIO will take the same track as ROSA in the medium term outlook.  If he becomes an issue down the line affecting our weather I’ll report on it well in advance.