Patchy marine layer low clouds and fog can be expected overnight and in the morning as high level clouds from Tropical Cyclone Marie move over the area this weekend. Periods of light to locally moderate precipitation are possible Saturday and Sunday. There is a slight (10-15%) chance of thunderstorms, mainly over the San Bernardino Mountains and High Desert on Sunday afternoon. Warmer and drier conditions Monday and Tuesday. Slight chance of mountain showers and thunderstorms return for mid-week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Hurricane Marie remains on a track toward the west-northwest with the center to remain well to the southwest of the area through the holiday weekend. The current NHC forecast has Marie weakening to a tropical storm on Sunday. The main impacts expected for Southern California over the weekend are increased surf, coastal flooding, and periods of light to locally moderate precipitation.
Mid to high level moisture from Marie will begin to increase from the south tonight into Saturday, increasing chances of showers for San Diego County. The moisture will continue to shift north Saturday into Sunday, increasing precipitation chances for Orange, Riverside, and San Bernardino Counties. For much of the area the most likely peak rainfall rates will be 0.20-0.40 inches per hour. There is a slight chance (10-15%) of thunderstorms over the San Bernardino mountains and High Desert Sunday afternoon. Current guidance indicates we'll be on the edge of the bulk of the instability. If the high cloud coverage is widespread enough to limit heating from the Sun any afternoon convection may be thwarted.
For this weekend, high temperatures will remain below average inland with highs near the coast running a few degrees above average. Overnight lows will also return to above average for this time of year by Sunday. By Wednesday, high temperatures will be within a few degrees of average for the mountains and deserts and a few to around 5 degrees above average for the coast and valleys. Above average low temperatures will be maintained into next weekend. High temperatures will gradually cool into next Friday.
The upper level flow turns south/southeasterly Wednesday and Thursday, which may allow for some additional moisture to creep into the area. There remains some uncertainty in the upper level pattern with the position of the upper level ridge over the southern US and a trough off the US West Coast. A more easterly position of the trough would result in drier conditions with a more westerly position of the ridge allowing more moisture into the area. Current forecast follows the NBM which has 20 to 35 percent chance of precipitation over the mountains Wednesday and Thursday afternoon and a slight chance of thunderstorms.
041800z, Coast/Valleys, Widespread VFR conditions expected through 03Z Saturday. Low clouds based 1800-2400 ft MSL will begin to move inland after 03Z Saturday with very patchy and intermittent coverage once again. Any low level clouds will clear very early Sat morning, likely by 12Z. Mid-level clouds 8000-10000 ft MSL will move in over the day Saturday, bringing chances for -SHRA which are not expected to bring any significant cig/vis changes.
Mountains/Deserts, VFR conditions prevail through the period. Breezy westerly winds mainly through mountain passes and along desert slopes. Gusts 25-35 kts with pockets of moderate up/downdrafts over and in lee of ridges. Winds taper off after 03Z Sat. Increasing mid-level clouds 8-10kft through Sat, bringing chances for -SHRA.
No hazardous marine conditions are expected through Tuesday.
A large south swell from Hurricane Marie will move into the region tonight and Saturday, peaking Sunday into Monday, before gradually diminishing Tuesday. This will result in elevated to high surf and strong rip and longshore currents at majority of beaches. Additionally, waves will occasionally run much farther up the beach than expected, especially during increasing and high tides.
For south and southwest-facing beaches, expecting high surf 6-10 feet. This includes Orange County and north San Diego County beaches. For west-facing beaches, expecting elevated surf 4-7 feet. This includes most of southern San Diego County beaches.
High surf combined with high astronomical tides 6 to about 6.8 feet will lead to tidal overflow and coastal flooding Saturday through Tuesday during evening high tides, especially for those south and southwest-facing beaches as well as low-lying, typically impacted areas.
Ca, Coastal Flood Advisory from 6 AM Saturday to 11 PM PDT Tuesday for Orange County Coastal Areas-San Diego County Coastal Areas.
High Surf Advisory from 6 AM Saturday to 11 PM PDT Tuesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
