Above average high and low temperatures will continue today, falling to around normal by Sunday. The cooling trend continues through the middle of next week. For Tuesday and Wednesday, increased high cloud cover is likely along with a 15 to 25 percent chance of light precipitation as moisture from Tropical Storm Karina potentially gets pulled northward. This tropical system is forecast to remain well to our south.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
Patchy low clouds have developed along the coast again this morning with just a few high clouds elsewhere. Low clouds and patchy fog are forecast to spread northward along the coast and a few miles inland through sunrise, clearing by mid-morning. Today will be the last day of the heat wave with temperatures a few degrees lower than yesterday. Highs will generally be in the low to mid 80s at the coast to the low 90s to low 100s for the inland coastal areas and valleys, mid 80s to mid 90s in the lower elevation mountains, mid 70s to mid 80s for the higher elevation mountains, mid to upper 90s in the high desert, and 105 to 112 in the low deserts. Monsoon moisture decreases today as flow aloft turns more southwesterly and precipitation chances this afternoon are less than 5%.
For Sunday through Wednesday, the upper level high which brought the relentless heat retreats to the Southeast US as upper level troughing develops along the West Coast. This pattern change will bring gradual cooling to So Cal. By Sunday, highs will finally return to late-August normals, falling to as much as 5 to 10 degrees below normal by Wednesday. This drier flow pattern will also offer some reprieve from the humidity and better cooling at night. Say goodbye to dew points in the 70s (for now). For Tuesday and Wednesday, there is still the potential from mid and upper level moisture from Tropical Storm Karina (which is forecast to become a hurricane later today), to be pulled northward into California. The storm itself is forecast to remain well to our south. Global ensembles still disagree greatly with respect to the amount of moisture that moves into our area. Some members of the GEFS and Canadian have Precipitable Water in excess of 2" and ensemble means near 1.5", while the EC ensemble is significantly drier due to differences in the track of the tropical system. Even with the increase in moisture, forcing will be weak, so if we do manage to get any precipitation it will most likely be light. For now PoPs remain around 15-25% for late Tuesday and Wednesday. Otherwise during this period expect the marine layer to rebuild and deepen, allowing low clouds and fog to spread slightly further into the coastal areas and far western valleys during the nights and mornings.
Thursday into next weekend, the upper level high begins to shift back westward, bringing warming and the potential return of monsoon moisture. High temperatures return to near average by Friday.
290930z, Coast, Low clouds based 400-700 ft MSL have become more widespread along the San Diego Co coastline and inland to about 10 miles, with vis 2-5 SM over higher coastal terrain. Clouds will creep into parts of southern OC, with ~30% chance for impacts vcnty KSNA through 15Z this morning. More widespread low clouds 600-1000 ft MSL will form after 06Z Sun, with impacts to coastal sites likely by 09Z.
Regionwide, Mostly clear skies except for periods FEW upper lvl clouds AOA 15kft.
Gusts around 20 knots expected this afternoon in the vicinity of San Clemete Island. Otherwise, no hazardous marine conditions are expected through Wednesday.
A 3-foot swell from the south-southwest (200 degrees) at 15-17 seconds moves into the region today and Sunday. This will bring localized elevated surf of 3-5 feet with sets to 6 feet, along with a high rip current risk to southwest-facing beaches, mostly in north San Diego County and Orange County.
Ca, Heat Advisory until 8 PM PDT this evening for Orange County Coastal Areas-San Diego County Coastal Areas.
Extreme Heat Warning until 8 PM PDT this evening for Coachella Valley-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Deserts-San Diego County Mountains-San Diego County Valleys- San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.
PZ, None.
