10/724 PM.
Moderate to damaging coastal flooding will likely continue through at least Tuesday. Periods of light to moderate rain and a low chance of thunderstorms will persist through Monday or Tuesday. Below normal temperatures will persist through Tuesday or Wednesday, then warming an developing offshore flow through the end of the week.
(Sat-Tue), 10/755 PM.
The most significant impacts over the short term will be COASTAL FLOODING RISKS. Please refer to Beaches section below as well as CFWLOX for further details on coastal flooding issues.
Tropical Storm Rachel is still forecast to track well south of Los Angeles. A pair of low pressure systems will drop from the north and interact with moisture from Rachel. This will result in below normal temperatures through Tuesday, as well as periods of light to moderate rain through Monday. Chances are highest on Sunday for the southern portion of our four county area, but widespread accumulating rain is very likely everywhere on Monday. Minor rain impacts are expected, focused the slick roads that might have some isolated spots of minor flooding. The one exception is the San Gabriel Mountains. While the heart of the deep tropical moisture plume from Rachel will stay east of Los Angeles County, several model projections wobble enough of the edge of the plume to produce 1-2 inches of rain on Sunday over the San Gabriels, with peak hourly rates around 0.5 inches per hour. This would be enough to cause some concerns from a mudslide or two in the mountain roads and canyons, as well as producing shallow debris flows over the Summit burn scar. This is something to keep and eye on.
As far as rainfall amounts are concerned, it appears the majority of our rainfall totals will come from the "first" system from late tonight into Sunday afternoon. Further details on the rain are below.
We are also expecting fairly breezy conditions for much of southwest California, especially in the mountains and deserts of eastern Los Angeles County. There will be a very sharp uptick in onshore pressure gradients Sunday morning along with the upper level influence of the second upper low dropping down south. A wind advisory has been issued for the San Gabriel Mountains as well as the Antelope Valley for Sunday, with gustiest winds expected during the afternoon through late evening hours.
Otherwise, much cooler temps will bring a relief to many after a long stretch of very hot weather.
Some details to note: - PWAT anomalies, associated with moisture from Rachel, will be 150-300% of normal. - PWATs will decrease on Monday. - There will continue to be a 5-10% chance of thunderstorms through Monday. - Rain totals today through Tuesday: - LA County: generally 0.25-1.00 inches except 1.50-2.50 inches over the San Gabriel Mountains (locally 3.00). - Ventura County: generally 0.10-0.50 inches with locally higher amounts possible over the mountains. - SBA/SLO Counties: generally under 0.25 inches. - Rainfall rates: generally under 0.25"/hour, but local rates up to around 0.50"/hour will be possible for LA County. Some recent higher resolution guidance suggests some rates in the Eastern San Gabriels may slightly exceed 0.50"/hour. - LA and Ventura Counties are under Marginal to Slight Risk for Excessive Rainfall on Sunday.
As has been stressed over the last few days, any changes in the track of Tropical Storm Rachel could bring noticeable changes to the expected rainfall for the area. So, stay tuned for the latest details.
(Wed-Sat), 10/1054 AM.
Wednesday will be more or less be a transition day from the cooler, active pattern to a warming and drying trend which will likely continue into the weekend. An upper level ridge of high pressure will build over the area and by Thursday we could see 500 mb heights reach 585-590 dam. Offshore flow is also poised to develop and these features will combine to bring this rapid warming and drying to southwest California. Widespread moderate heat risk is likely for the coasts and coastal valleys Thursday through the weekend, with low chances of major heat risk. The magnitude of temperatures will likely depend on the magnitude of the offshore flow, but a weak to at least locally moderate Santa Ana Wind event is likely.
11/0415z.
At 0400Z at KLAX, there was neither a marine layer nor a marine inversion.
Overall, moderate confidence in 06Z TAF package. Moisture streaming northward from Tropical Storm Rachel will bring the threat of showers to all sites at times through the TAF period. The best chances for showers will be over Los Angeles county with lesser chances north and west. There is a 40% chance of MVFR CIGs at all sites through this evening. Additionally, there is a 5-10% chance of thunderstorms through this afternoon.
KLAX, Moderate confidence in 06Z TAF. There is a 40% chance of MVFR CIGs in the 15Z-02Z time frame. There is a 20-30% chance of easterly winds around 8 knots through 22Z.
KBUR, Moderate confidence in 06Z TAF. There is a 40% chance of MVFR CIGs in the 15Z-02Z time frame.
10/756 PM.
For the Outer Waters, moderate to high confidence in current forecast. High confidence in a combination of at least SCA level winds and seas through Monday evening for the waters near and NW of Point Conception. There is a 30% chance of Gale Force winds early Sunday morning, then the winds are expected to drop below SCA levels Sunday evening. However, steep seas of 10+ feet will likely persist into at least Monday morning and possibly into Monday evening. On Tuesday, there is a 50% chance of SCA level winds around Point Conception with winds remaining below SCA levels elsewhere.
For the Inner Waters north of Point Sal, high confidence in current forecast of SCA winds through Sunday evening. There will be a chance of SCA conds again Tuesday evening, with a 30-50% chance.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. From this evening through Sunday evening, there is a 60-80% chance of SCA level winds and seas. For Monday through Wednesday, high confidence in winds and seas remaining below SCA levels for most of the southern Inner Waters. The exception will be the western half of the Santa Barbara Channel with a 50% chance of SCA level winds late Tuesday afternoon through Tuesday evening.
Periods of light to moderate showers are likely through Tuesday, with highest confidence for Sunday-Monday. There is a 10% chance of thunderstorms during the same time frame. While showers or thunderstorms are possible anywhere, the highest chances exist south of Point Conception.
Long period swell from the west and the south are affecting the coastal waters, and can create a confused sea state. This can make boating more challenging and dangerous, especially for small vessels.
10/805 PM.
Earlier this morning, LA Harbor Tide Gauge reported a peak of 7.7 feet, approximately 1.6 feet above predicted astronomical high tides.
A Coastal Flood Warning is in effect for the beaches of Los Angeles County (including Long Beach, the Malibu Coast and Catalina Island) through 3 PM Sunday. DAMAGING sea-water coastal flooding is likely through Sunday, especially near the Sunday morning high tide where anticipated tide levels are expected to be around 8 feet. The most likely areas for DAMAGING coastal flooding on Sunday morning will be vulnerable south-facing beaches due to the expected combination of very high tides around 8 feet (including additive effect of low barometric pressure and onshore winds gusting to 15 to 25 mph), high surf of 5 to 8 feet, and light to moderate rainfall. THERE IS GROWING CONFIDENCE THAT THE EXPECTED COASTAL FLOODING IMPACTS ON SUNDAY MORNING FOR VULNERABLE SOUTH FACING BEACHES OF LA COUNTY COULD BE THE MOST SIGNIFICANT WE HAVE SEEN SO FAR THIS SEASON, INCLUDING THOSE SEEN WITH Marie.
For all other beaches and harbors of LA county, minor to moderate sea- water flooding will likely impact beaches and walkways, especially with the Sunday morning high tide which could cause local damage to the most vulnerable locations such as Venice and Long Beach. For all beach areas, significant erosion is expected. There is an increased risk of ocean drowning. Dangerous and life- threatening rip currents can pull swimmers and surfers out to sea. Large breaking waves can cause injury, wash people off beaches and rocks, and capsize small boats near shore. The projected high tides of around 8 feet for Sunday morning would approach or exceed recent record tide levels for LA county. Large secondary high tides are also expected each evening.
For beaches from Ventura County northward, minor to moderate coastal flooding will be likely near times of high tide as well as periods of elevated to high surf and strong rip currents. In addition to the Coastal Flood Advisory for Ventura County, Coastal Flood Advisories have been added for the Central Coast and southern Santa Barbara coast. For Ventura county, there is the possibility of localized damage across low-lying areas during the Sunday morning high tide, along with the threat of significant sea spray and and water on sections of PCH between Point Mugu and Sycamore Cove.
A very complex series of swells from the south, west, and northwest will impact our coastlines into at least early next week. Energy from Tropical Storm Rachel, southern hemisphere swells, northwest swells, and local wind swells will add up with each other to produce the aforementioned coastal impacts. Please continue to monitor the forecast.
Ca, Coastal Flood Warning in effect until 3 PM PDT Sunday for zones 87-362-366. (See LAXCFWLOX). Coastal Flood Advisory in effect from 3 PM Sunday to 2 PM PDT Tuesday for zones 87-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect until 6 AM PDT Sunday for zones 340-346. (See LAXCFWLOX). Coastal Flood Advisory in effect from 6 AM Sunday to 10 PM PDT Monday for zones 340-346-349-350. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM Sunday to 10 PM PDT Monday for zones 340-346. (See LAXCFWLOX). Beach Hazards Statement in effect through Tuesday afternoon for zones 349-350. (See LAXCFWLOX). Coastal Flood Advisory in effect until 2 PM PDT Tuesday for zone 354. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM to 10 PM PDT Sunday for zones 354-362-366. (See LAXCFWLOX). Wind Advisory in effect from 5 AM Sunday to 5 AM PDT Monday for zones 378>383. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 9 PM PDT Sunday for zones 645-650-655-676. (See LAXMWWLOX). Small Craft Advisory in effect until 5 PM PDT Monday for zones 670-673. (See LAXMWWLOX).
