After a relatively stagnant hot pattern throughout much of September, we are going to experience a major weather shift the next 5-7 days.
The computer models are ALL over the place and are having a very difficult time with the precise details, so I would suggest everyone focuses on the overall pattern changes ahead. The specific timing is going to be difficult to predict, but the screaming message is we have the potential for a variety of weather between Sunday and Wednesday, including:
Much Cooler Temps
WHAT IS RESPONSIBLE FOR THIS IMPENDING STORMY WEATHER?
A complex weather pattern is setting up. Several factors are coming together that are typically very difficult to forecast with precision.
First, a cold low pressure system, one of the first of the fall season, is expected to strengthen off the coast of California, and move slowly to the southeast toward our area. This system will contain some dynamics and unstable air.
Second, powerful hurricane Rosa is located southwest of Baja California. This system is expected to start moving north toward northern Baja over the weekend.
As the colder low pressure system moves closer to California, the circulation around this system will absorb hurricane Rosa into its wind patterns, allowing the hurricane to be directed toward northern Baja. The incredibly moist tropical airmass will move north into Southern California, Southern Nevada, and much of Arizona starting Sunday afternoon and continuing into Monday. This will likely bring higher humidity (sorry, but not for long!) and some gusty southeast winds and haze to the Coachella Valley.
The hurricane will lose much of its strength as it approaches Baja south of Ensenada. However, it may still produce winds of 45 mph and be a significant Tropical Storm. It’s relatively rare for a landfalling tropical system this close to our area.
The second phase of the storm is expected on Tuesday, possibly a little longer. The low pressure system off the coast will move over our area, bringing scattered showers and thunderstorms. Rainfall amounts will likely be highly variable, with the potential for locally heavy rains in some areas, and dry weather in others.
I would caution anyone from getting hung up on the exact details at this point, since a lot of uncertainty still exists. However, there is a good chance that some areas of the deserts and nearby mountains could see 0.5 - 1 inch of rain, with scattered amounts of 1 - 3 inches or more. It is possible the heavy thunderstorms could dump even more than that in localized areas, if they occur. Some areas may see much less rain. It’s possible some areas will see nothing.
However, it is important that people remain cautious between late Sunday and Tuesday, for the possibility of flash flooding, localized heavy rain and storms. It appears the heaviest rain is likely over Arizona, so anyone traveling to the east Sunday - Tuesday should be alert for any weather warnings or flash flood warnings.
This weather setup has the potential to cause significant problems. Any recent burn areas, like those near Idyllwild, or in the burn areas Orange County, should be alert to the potential for flash floods and mudslides if heavy rain develops.
This system is expected to finally break our hot weather pattern, with high temperatures falling into the 80s and 90s next week. Overnight lows are likely to drop Ito the 60s several days as well. I can’t speak for anyone else, but I am done with the nagging heat this season. Bring on the cooler weather! If you see someone doing cartwheels next week, it could be me. I’m not sure I can contain my excitement for the drop of temperatures!
Once the tropical portion of the system moves east, it will be replaced by a cooler airmass off the Pacific, that appears to stick around for much of next week. Temperatures will gradually climb back into the 90s later next week… but the relief from the 100+ degree days will undoubtedly bring many of us out of hibernation!
Let’s hope we escape any damaging floods, but get some beneficial rains this week! Incidentally, anyone traveling to the high Sierras should be aware they may experience their first significant snowfall of the season as well. Change is near!