Cloudy and cooler today along with a slight chance of light showers for our southeastern regions through early Monday. The main trough moves through Monday, bringing back the marine layer and breezy conditions to the mountains and deserts. Weak high pressure will then bring dry and warmer weather Tuesday into next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION/MARINE/BEACHES DISCUSSION,
Satellite shows upper level clouds streaming through the region, sourced from moisture from Hurricane Odalys hundreds of miles to the south-southwest and carried through the jet stream. The 00z 9/26 sounding shows a shallow moist profile at around 25,000 feet, which is expected to deepen down to around 10,000 feet by this afternoon.
Today through Monday, Despite the near surface remaining drier, PWAT's today will increase to around 1.50" for San Diego County and deserts east of the mountains, enough for extensive cloud cover throughout the day but not enough for precipitation without any background instability or forcing. As a result, precip chances above 10% have been reduced to southeastern portions of San Diego County and other mountain peaks from this afternoon through early Monday morning. Elsewhere, virga showers aloft may bring some sprinkles to briefly reach the ground. Because of the cloud cover region-wide, high temperatures will be noticeably cooler today relative to yesterday, around 6-12 degrees cooler. A sharp boundary of drier air aloft moves through SoCal during the day Monday, out ahead of the trough axis, which barely dips south enough to bring cooler temperatures aloft and thus cooler daytime temperatures despite increasing sunshine. Monday will be the coolest day of the week by far with highs 75-85 degrees across the coastal basin, 60s for the mountains and mid-90s in the lower deserts. With the troughs gradual passage in the afternoon, onshore winds will be breezy east of mountain passes and along desert slopes (25-35 mph, higher through Banning Pass) and the marine later will build into the evening, with low clouds likely Monday night for much of the coastal basin.
Tuesday, With the trough axis moving east, a weak offshore gradient between the Coastal Basin and the High Desert coupled with modest northerly flow aloft will bring a decent (60%) chance for weak northerly offshore flow. This would noticeably drop the relative humidity Monday night into Tuesday for the deserts, mountains and Inland Empire (especially near the Cajon Pass). High temperatures increase noticeably to mid-80s to low-90s across the Coastal Basin with perhaps a few low 80s at the coast.
Wednesday through the weekend, While offshore winds dissipate Wednesday, daytime temperatures increase through the end of the week while relative humidities generally continue to decrease for inland areas. A ridge will be slowly developing out in the Pacific, moving toward the southwest US through the end of the week.
By the end of the week, daytime RH's drop to 15-25% for elevated interior valleys, the Inland Empire, mountains and deserts (locally down to 10% in the High Desert) while temperatures reach into the mid-90s to low-100s in these areas. Even the lowland urban areas just a few miles inland of the coast will likely (50-80% chance) reach at least into the upper 80s and perhaps (20-60% chance) above 90F for Thurs/Fri/Sat.
271145z, Coast/Valleys, BKN-OVC high clouds AOA 15,000ft MSL will continue for much of the TAF period. Very patchy low clouds mainly offshore should stay over the waters this morning, where cigs are near 500-800 ft MSL. Low clouds clearing completely by 15Z. Increasing confidence on very patchy low clouds (if any) forming tonight, with minimal cigs for coastal TAF sites through Monday morning.
Mountains/Deserts, VFR prevails with BKN-OVC clouds 10-20 kft through the period. Pockets of -SHRA possible between 00-14Z Monday, little to no surface impact, but some brief lower cigs below 5000ft possible. Best chance in eastern San Diego County.
There will likely be northwest wind gusts of 20-25 knots in the outer waters Monday afternoon and evening, accompanied by choppy mixed seas. Otherwise, no hazardous marine conditions are expected through Thursday.
Southwesterly swell (3-4 ft at 13 seconds from ~200 degrees) from Hurricane Odalys persists through this weekend, bringing surf of 3-5 feet with sets up to 6 feet, highest along south and southwest facing beaches. The swell from Hurricane Polo (3 ft at 14 seconds from ~180 degrees) then increases on Monday. Given this direction, most of San Diego County beaches will be largely sheltered from this swell, but Orange County beaches (especially in north OC) should be impacted. Meanwhile, a northwesterly swell (3-4 ft at 7 seconds from ~280 degrees) arrives later today and Monday. Between these two swells, surf of 3-5 feet with sets to 7 feet looks probable along south/southwest facing beaches with surf 3-5 feet along west-facing beaches through Tuesday. With this elevated surf, there is a high risk for rip currents through Tuesday.
Tides are already observed over 6.2 feet and are expected to gradually increase into early next week, peaking around 7.0ft for the late-morning high tides on Monday-Wednesday, highest on Tuesday. A Beach Hazard Statement remains in effect through tonight due to the risk of minor tidal overflow and minor coastal erosion. A Coastal Flood Advisory is in effect from early Monday morning through Wednesday afternoon to account for the highest tides combining with the expected elevated surf. Primary impacts during the morning high tides Monday-Wednesday will be minor coastal flooding in low lying areas in addition to coastal erosion.
Please note - listed tide predictions have been adjusted to reflect actual measured tide observations.
Ca, Beach Hazards Statement through late tonight for Orange County Coastal Areas-San Diego County Coastal Areas.
Coastal Flood Advisory from 5 AM Monday to 5 PM PDT Wednesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
