Heat continues today with high and low temperatures well above normal. Slight chance of showers and thunderstorms for the mountains and locally into the deserts this afternoon. Gradual cooling this weekend with temperatures falling below normal by early next week. For Tuesday and Wednesday of next week, increased high cloud cover is likely along with a 20 to 30 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,
Scattered high clouds ahead of the trough off the west Coast continue to drift northeast over the area this morning. Patches of low clouds and fog are developing over the San Diego County coastal areas. Fog may become locally dense towards sunrise, especially on the coastal mesas. Any low clouds and fog should quickly clear out by mid-morning.
One last day of excruciating heat is in store with high temperatures around 5 to 10 degrees above normal. With far less cloud cover than yesterday and minimal cooling this morning, it will be several degrees warmer than what ended up occurring yesterday, especially across the low deserts. The Heat Advisories and Excessive Heat Warnings all remain in effect through 8 PM this evening. Modest mid-level moisture remains for a slight chance of showers and thunderstorms over the mountains this afternoon. With flow aloft turning more southwesterly, a few of these storms could drift into the low desert.
The upper level high begins to progress eastward as an upper trough pushes into the West Coast on Saturday. This will bring a few degrees of cooling across the area, though unfortunately the humidity will stick around. This trough will remain somewhat stationary through early next week as multiple short waves move through the mean flow to our north. This will continue the cooling trend into at least Tuesday. By Sunday, high temperatures will finally return to normal, though the humidity will keep minimum temperatures around 5 degrees above normal. By Tuesday, highs will be around 5 to 10 degrees below normal. Subtle drying also allows low temperatures to return to near normal.
For late Tuesday into Thursday, there's around a 15% chance of moistly light showers as mid and upper level moisture from what is currently Tropical Storm Karina potentially gets drawn north. How much moisture we get and any forcing that goes along with it will be very sensitive to the track of the tropical cyclone as well as the position of the upper trough off the West Coast. There is a lot of spread in the forecast precipitable water from the ensembles, and to a greater extent the amount of rainfall we could get from it. It should be noted that the official NHC track forecast for this cyclone remains well to our south, so these small rain chances and increased surf are the only impact we are anticipating from this system.
Minor warming is possible late in the week as high pressure tries to expand westward again, though the warmest ensemble solutions only account for about 40% of the ensemble space at this point, with the remaining 60% keeping temperatures closer to midweek values.
280930z, Coast, Low clouds based 400-700 ft MSL will continue to become more widespread through coastal SD County, as mid to upper level clouds move northwards out of the area, though likely will remain patchy for most of the night. Best chances for impacts for coastal sites is through 15Z, with vis restrictions 2-5 SM over higher coastal terrain. Low clouds expected to clear by 16Z, with low clouds of similar bases/patchiness forming after 09Z Sat.
Mountains/Deserts, Cumulus based around 9,000ft MSL over the mountains today 20Z to Sat 01Z with isolated CB cloud tops rising to 40,000ft MSL. There is a 10-15% chance of iso TSRA/SHRA over the mountains and a 5-10% chance in the deserts until 01Z Sat. Any TS that develops could produce gusty, erratic winds.
Regionwide, High clouds AOA 15,000ft MSL will continue this morning and afternoon, decreasing through this evening.
No hazardous marine conditions are expected through Tuesday.
A fresh 3 foot swell from the south-southwest (200 degrees) at 15-17 seconds moves into the region Saturday-Sunday. This will bring localized elevated surf of 4-6 feet 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-Riverside County Mountains-San Bernardino County Mountains-San Diego County Coastal Areas.
Extreme Heat Warning until 8 PM PDT this evening for Apple and Lucerne Valleys-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.
