Cooling will spread inland into the weekend with high temperatures cooling to around average on Saturday. High temperatures for the coast and valleys will be mostly in the 70s for Sunday through Tuesday. One low pressure system from the southwest on Sunday and a second from the north on Monday and Tuesday combined with tropical moisture will bring showers for late Saturday night through Sunday night with continuing chances for showers through Tuesday night. There will also be stronger southwest to west winds on Sunday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Tonight through Saturday,
The ridge is continuing to break down, which is allowing for a cooling trend beginning today into tomorrow, and then even moreso on Saturday as we begin to become influenced by an approaching trough and tropical system moving into the region. Mostly clear skies will persist through tomorrow, with improving onshore flow and likely some slightly better coverage developing overnight with the marine layer, with ceilings generally around 500 to 1000 ft MSL. There will also be some patchy fog developing within the higher inland valleys again, although a little further inland as ceilings are expected to rise a little higher from where they were the previous night. Much cooler temperatures will be felt on Saturday, along with increasing low to mid level storm clouds and a slight chance of a few rain showers developing by later in the evening as a deepening trough upstream is met with the tropical cyclone (currently a hurricane), Rachel, continues to approach the region. As a result, highs by Saturday will be back to being either at, or slightly below, the seasonal average for this time of year.
Sunday through Thursday,
Depending on the track of Rachel, there could be substantial impacts to the region, in terms of heavy rainfall and the risk of flash flooding, along with strong and gusty winds. An overall consensus of the latest forecast member tracks have the system potentially making landfall somewhere between Punta San Carlos and Ensenada, in Northern Baja California, Mexico. However, there are a few of the members, and even the latest 12Z GFS model run which has this storm moving further north and up into the SOCAL bight, deepening down to 977 DM with further intensification as it nears the coastal areas of San Diego and Orange Counties, with a possible landfall occurring during the early morning of Sunday. The important aspect to note with Rachel is that it is going to obtain a lot of moisture with it, as PWATs increase to nearly 600% as it is churning over the Pacific waters well to our southwest through tomorrow, and these high PWATs will maintain a nearly 350-400% capacity as this system eventually propagates over southern California by later this weekend. What this translates to is the potential for moderate to heavy rainfall rates, that may occur with some of these heavier showers and/or thunderstorms embedded within the rain shield associated with Rachel as it transitions over the area. Because of this, confidence of rainfall rates exceeding the 0.40 inches per hour for the coastal/inland areas, and up to 0.60 inches for the mountains/adjacent deserts, and 0.50 inch per hour rates for the lower deserts/Coachella Valley, is quite high. Despite this, confidence of total rainfall rates remains low, and is almost exclusively depended on the track of Rachel, where she decides to make landfall, and whether or not she maintains her tropical storm status all the way to the region. Moreover, there will also be a secondary wave transitioning over the region on Monday, and keeping a chance of rain continuing through then, although considerably less amounts expected. As of now, the highest rainfall rates are expected along the southern facing slopes of the San Bernardino Mountains, with amounts generally 1.00-1.25 inches, and locally up to 1.5 inches for some of the highest elevations. Due to this, WPC has included our CWA in a marginal outlook for excessive rainfall from the mountains to the deserts, and slight for the deserts. In addition, strong and gusty winds could also cause for the need of wind advisories. There will also be increased swell and wave action, which may further contribute to erosion and possible coastal flooding for some of the low-lying areas. All of this will depend on the track of Rachel, so please stay tuned for updates to this system and changes to our forecast as we continue to know more about the potential impacts from Rachel to southern California. Showers will continue into Monday as the secondary low moves over the region and high pressure slowly builds back in. Temperatures will begin to rebound a bit, but remain on the cooler side through next Thursday.
081830z, Coast, SKC and VFR through the afternoon and evening. Patchy low clouds and fog based around 600-800 feet MSL develop over coastal areas starting 06-08z Fri. Clouds slowly expand in coverage overnight reaching 10-15 miles inland. Minor vis reductions (1-5SM) expected for elevated coastal terrain and western valleys. Clouds scatter back toward the coastline 15-17z Fri.
Otherwise, mostly clear through Friday morning, except for shallow cumulus over mountains 19-01Z.
No hazardous marine conditions are expected through Saturday. The remnants of Rachel will bring a rapid increase in southerly swell along with gusty winds and choppy seas Sunday, diminishing somewhat on Monday.
Surf of 3-5 feet with sets to 6 feet is expected on south and southwest facing beaches through Friday. Elevated surf and strong rip and longshore currents will create hazardous swimming conditions. This elevated surf will combine with high tides during the mornings and evenings to generate local coastal flooding and beach erosion.
Another south swell arriving Sunday along with wind waves and continued morning high tides near 7 feet will maintain a threat of coastal flooding and beach erosion into Tuesday. Surf on Sunday is currently expected to be 6-9 feet, decreasing to 3-6 feet for Monday and Tuesday. There is still a lot of uncertainty in exact surf heights for now. The Beach Hazards Statement and Coastal Flood Advisory contain more details.
Ca, Extreme Heat Warning until 8 PM PDT this evening for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Coastal Areas-San Diego County Valleys- Santa Ana Mountains and Foothills.
Beach Hazards Statement through Friday evening for Orange County Coastal Areas-San Diego County Coastal Areas.
Coastal Flood Advisory until 2 PM PDT Tuesday for Orange County Coastal Areas-San Diego County Coastal Areas.
Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley- San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
