04/336 AM.
Below normal temperatures, patchy marine layer clouds, and breezy onshore winds will continue today. Tropical Cyclone Marie, which will remain well offshore of SoCal, will bring impacts to the region over the weekend into early next week. Rain is favored for Sunday focused over Los Angeles County. Increasing southerly swell will create hazardous surf conditions at the coasts.
(tdy-Sun), 04/934 AM.
***UPDATE***
Focus will remain impacts from Hurricane Marie, which is forecast to track northwest over the next several days but still remain well off the California Coast. Some rainfall is expected, but totals still look to be around 0.25 inches or less for most population centers. One impact of note, is that roads will be quite slick with any wetting rainfall due to the build up of oils over the last several months.
***From Previous Discussion***
We have high confidence in potentially deadly rip currents and large waves this holiday weekend focused across south facing beaches (spreading north from Marie). Please consider swimming near a lifeguard and check in with the lifeguard if you or a loved one is an inexperienced ocean swimmer. Please see the beaches section below for details on this threat.
Otherwise forecast confidence dwindles quickly this weekend, especially into Sunday as a unseasonably persistent trough near the West Coast will likely merges with moisture well in advance of slowly weakening Tropical Cyclone Marie. We have increasing confidence in light to moderate rain as early as Saturday evening but especially into Sunday is quite likely (50-80 percent chance) for LA County, quickly dwindling westward (20-50 percent) chance for Ventura/Santa Barbara County and less than 20 percent chance for San Luis Obispo County. The bullseye of this activity could feasibly shift as far north of Ventura County or as far south as Orange County.
This is a very rare pattern for our part of the country, especially in early September, as a strong (for early September), favorable part of a jet stream peaking near 120 kt interacts with the tropical moisture (precipitable waters may approach incredible values of 2 inches across portions of LA County) and moderate lapse rates to support scattered mainly light to moderate showers. However, there is a 5 percent chance of excessive rainfall with minor flooding in embedded heavier showers or thunderstorms (5-15 percent chance) focused across the LA County mountains and urban areas. While any embedded heavier showers or thunderstorms will mostly be moving at decent pace, any stalled or training cells could produce greater than a quarter of an inch in an hour. Rainfall totals as a whole will be less than a half of an inch (probably under a quarter of an inch where most people live), focused across LA County, isolated higher amounts will be possible, especially coastal facing mountains.
The increased cloud cover this weekend, especially into Sunday, will likely disrupt typical diurnal winds (including Sundowners) and should trend weaker accordingly. It will feel warmer especially near the coast and outside of rain, as humidity increases once again, especially from Santa Barbara County and south. Although daytime temperatures probably will not warm too much for most areas, overnight lows could be quite warm and only into the 70s for our southern coasts and coastal valleys where clouds persist into the overnight Saturday.
(Mon-Thu), 04/449 AM.
Well below normal forecast confidence continues into the extended period as an unusually active jet stream continues to be near and possibly phasing with tropical moisture from what's left of Marie at times.
A break in the action is possible early next week, although lingering moisture may be able to squeeze out drizzle or an occasional shower. A warming trend is most likely with near to slightly above normal temperatures.
Southwest California may become sandwiched between a ridge to the southeast and a pesky trough to the west for the middle to end of the week, keeping the door open for additional tropical moisture. The associated southwest flow aloft may bring unsettled weather, although timing, location, and potential impacts are uncertain that far out.
04/1646z.
At 1630Z at KLAX, the marine layer was 2600 feet deep. The top of the inversion was 4700 feet with a temperature of 17 degrees Celsius.
For 18Z TAF package, high confidence in CAVU conditions for valley and desert TAFs. For coastal sites, moderate confidence 18Z TAFs due to uncertainties with development of marine layer clouds.
KLAX, Moderate confidence in 18Z TAF. Timing of return of MVFR CIGs could be +/- 3 hours of current 11Z forecast. There is a 30% chance that CIG/VSBY restrictions do not develop overnight. No significant easterly wind component is expected
KBUR, High confidence in 18Z TAF as CAVU conditions are expected through the period.
04/804 AM.
For the Outer Waters, moderate confidence in current forecast. Today through Saturday, there is a 30-40% chance of Small Craft Advisory (SCA) level winds, mainly around Point Conception. On Sunday, there is a 50-70% chance of SCA level winds across all of the Outer Waters. For Monday through Tuesday, the chances for SCA level winds decreases to 20-30%, with the best chances around Point Conception.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Saturday, high confidence in winds and seas remaining below SCA levels. On Sunday, there is a 60-70% chance of SCA level winds in the afternoon and evening hours. For Monday through Tuesday, there is a 20-30% chance of SCA level winds in the afternoon and evening hours.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. For a majority of the southern Inner Waters, high confidence in winds and seas remaining below SCA levels. The only exception will be the western half of the Santa Barbara Channel where there will be 40-50% chance of SCA level winds late Sunday afternoon and evening.
Tropical moisture will approach the area Sunday through at least Tuesday. While unlikely at this point, there is a 5 to 10 percent chance of a thunderstorm over the coastal waters, highest south of Point Conception. A large south swell will also impact the area, causing increased currents and surges in the vulnerable harbors.
04/804 AM.
The range of swell and surf outcomes have tightened, with peak south swell associated with Hurricane Marie likely in that 5 to 8 foot range. With moderate periods of 12 to 14 seconds, surf heights on exposed south-facing shores should be of similar height (5-8 feet). Some spots might see larger waves (like Malibu). The Santa Barbara South Coast will be largely protected from this swell, but there are some small windows of southeasterly and southwesterly energy that could cause boosts in the waves. HIGH SURF ADVISORIES remain in place for Los Angeles and Ventura Counties, with BEACH HAZARDS STATEMENTS (a step below high surf advisories) in effect for Santa Barbara and San Luis Obispo Counties. With huge crowds expected at the beaches for the Labor Day holiday, the emphasis for these statements is to alert the public to be extra careful in and near the ocean.
High tides will also be increasing through early next week. Due to a variety of reasons, the actual observed tides have been running 6 inches above predictions for sometime now. The south swell will likely enhance that enhancement. As a result, high tides should exceed 7 feet by Monday. Adding large tides like that with the south swell will result in a moderate risk for coastal flooding over the vulnerable south-facing shores. Areas of most concern include Avalon, Long Beach (Alamitos Peninsula), Malibu, and Point Mugu. COASTAL FLOOD ADVISORIES remain in effect for Los Angeles and Ventura Counties where the best combination of tides and waves will occur, but Santa Barbara and San Luis Obispo Counties could also see some isolated issues.
Ca, Coastal Flood Advisory in effect from 6 AM Saturday to 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM Saturday to 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect from Saturday morning through Tuesday evening for zones 340-346-349-350. (See LAXCFWLOX). PZ, NONE.
