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), 04/339 AM.
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), 04/342 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.
04/1142z.
At 08Z at KLAX, a moist layer was around 2500 ft with no inversion.
High confidence in VFR TAFs for desert airfields (KPMD & KWJF).
Moderate confidence KSMX and north and low confidence for other coastal and coastal valley TAFs with a 30-50 percent chance that VFR conds prevail. Where cigs/vsbys occur, MVFR will be most common but may improve to VFR before scattering out for most terminals 15-18Z.
Moderate confidence that tonight will tend to be improved save for KSMX and KSBP where there is a 30-50 percent chance of IFR to low MVFR cigs/vsbys starting 05Z-09Z.
KLAX, Low confidence in TAF with a 30 percent chance that VFR conds prevail. Good confidence that any east wind component will remain below 6 kt.
KBUR, Low confidence in TAF with a 40-50 percent chance that VFR conds prevail.
04/134 AM.
Small Craft Advisory (SCA) winds will be common each afternoon and night for the offshore waters off the Central Coast for the foreseeable future. All of other waters should stay below SCA.
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.
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.
