08/242 AM.
Today will be the last day of the long lasting heat wave. Although afternoon high temperatures will be a few degrees cooler than yesterday they will still be dangerously high. Temperatures will trend cooler Friday into Sunday and there will be an increasing chance of showers and thunderstorms due to moisture from Hurricane Rachel.
(tdy-Sat), 08/943 AM.
***UPDATE***
Today is the last day of any lingering heat hazards as pressure gradients have finally crossed over to lightly onshore as of this morning. Temperatures today are expected to at least 1-3 degrees cooler, but as much as 4-8 degrees cooler closer to the coast.
Rachel has started to take a more northerly track, and will soon be moving to the northeast and weakening to a remnant low. The latest official track has Rachel moving onshore at around 150 miles south of the US/MX border. There will be increasing impacts to beach areas as the next couple days, peaking Sunday. And as far as rain chances, it's still looking pretty favorable. It's a little complicated with the upper low moving into the area just following the moisture from Rachel. With this scenario, rain chances will begin first in LA County with Rachel moisture on Sunday, then rain chances with the upper low over the the Central Coast Monday and moving into areas south of Pt Conception Monday afternoon into early Tuesday. Amounts are still very uncertain at this time, but anywhere from just some light showers to a half to one inch in parts of LA County.
***From Previous Discussion***
Changes will really become noticeable on Friday as an upper low develops to the west of Pt Conception and begins to move to the east. Hgts will fall through the day to 580 dam. At the same time an early season cold upper low will begin to move out of Canada and into Washington State. Onshore flow will continue to increase and there should be a fairly robust marine layer cloud deck covering most of the coasts and some of the lower vlys. Most temps will fall by about 6 degrees, but the near shore area will not see much change as those areas will see the best cooling today.
Things get really interesting on Saturday as major troffing will develop across all of the west coast and set up SW flow across the entire state and the Baja Peninsula. This SW flow will steer TS Rachel to the NE and by late afternoon Rachel should be ~450 S of San Diego. It will be a mostly cloudy day 1st due to a widespread and deep marine layer that will cover all of the csts and vlys and then due to clouds streaming off of Rachel. SLO and portions of SBA counties will probably be partly cloudy in the afternoon as the mid level clouds will be more focused over the southern counties. The combination of 574 dam hgts , plenty of clouds, a deep marine layer and increased onshore flow will bring dramatic cooling to the entire area. Look for 6 to 12 degrees of cooling almost everywhere (The beaches of the Central Coast will have already cooled down today and Friday). Most coastal temps will be in the lower to mid 70s with a few upper 70s across the interior coastal sections of LA county. The vlys will only warm into upper 70s and lower 80s. Most max temps will end up 3 to 6 degrees blo normal.
Enough moisture from Rachel will move up into VTA and LA counties Saturday night to warrant a slight chc of rain with potential rainfall amounts up to a tenth of an inch.
(Sun-Wed), 08/243 AM.
A fairly complicated weather pattern occurs on Sunday. A very large pos tilt trof will drape itself across the entire west coast. It will not move much at all, rather a cold upper low will plunge to SW down the trof axis and will sit atop of the Bay Area by late afternoon. Hgts over Srn CA will fall to 565 dam. On top (well actually below) all of this tropical storm Rachel will move into the northern portion of the Baja Peninsula and will send a surge of moisture into the trof over Srn CA. A chc of rain will develop over SBA/VTA and esp LA counties in the predawn hours and will continue through the evening. In general a tenth of an inch of rain is possible for any given 6 hour period during the day with heavier amounts across eastern LA county. Rainfall from midnight to midnight looks to be little or nothing for SLO county, a trace to .20 for SBA county, a tenth to about a third of an inch for VTA county and a quarter to a half inch for most of LA county but .75 to 1.5 inches of rain is possible for the eastern San Gabriel Mtns and its coastal foothills. There will also be 5-10% chance of TSTMs over LA and VTA counties with the best chc over LA county. Max temps will range from the mid 60s to mid 70s.
On Monday the upper low will move into the vcnty of SBA county with 557 dam hgts. The low will bring clouds and chc of rain to the entire 4 county forecast area from midnight to midnight. Since most of the moisture will be to the east of the area rainfall totals will not be that great most areas can expect to recieve a tenth to a quarter inch of rainfall. Max temps will fall further to the mid 60s to lower 70s.
There is some disagreement on how fast the upper low will move out of the area. Enough solutions keep the upper low around long enough to keep a 20 to 30 percent chc of rain in the forecast. Even if it does rain there will not be much additional rainfall.
Aside from a small chc of a mtn shower Wednesday should be dry as drier NW flow moves into and over the state. Sunnier skies and rising temps will bring 3 to 6 degrees of warming. Even with the warming max temps will end up about 6 degrees blo normal.
08/1751z.
At around 17Z at KLAX, the marine layer was 500 feet deep. The top of the inversion was 1700 feet with a temperature of 28 C.
High confidence in VFR conditions at KPRB, KVNY, KBUR, KPMD, and KWJF, with a 10% chance of brief LIFR conds 13Z-17Z at KPRB/KVNY/KBUR.
Moderate confidence in remaining TAFs with slightly higher CIGs compared to last night. Min cig height may be off +/- 300 feet and arrival may be off 2 hours. There is a 20% chance KSMX/KSBP remain above VLIFR conds tonight. 10% chance for 1/4SM FG at KOXR/KCMA.
KLAX, Moderate confidence in TAF. Gusty onshore winds will be common this afternoon/evening. CIG heights may be off +/- 300 feet and cigs may arrive as early as 06Z. No significant easterly wind component is expected.
KBUR, High confidence in VFR TAF with a 10% chance for LIFR conds 13Z-17Z.
08/852 AM.
Relatively quiet conditions are expected across the coastal waters through much of Saturday. Localized Small Craft Advisory (SCA) gusts may occur each afternoon and evening between Point Conception and San Nicolas Island. Night through morning dense fog may affect portions of the coastal waters adjacent to the Central Coast and south to San Nicolas Island.
Northwest to southwest winds will increase to at least 20-30 knots by Saturday afternoon/evening, becoming much more expansive all of Sunday and into Monday morning. There is a 40-50% chance of Gale Force winds on Sunday, primarily focused across the nearshore waters adjacent to Los Angeles and Orange Counties. Large, steep, and choppy seas will develop Saturday, continuing through at least Monday. This fairly rapid and significant change in the winds is due to a very complex situation as an unseasonably cold trough drops down the California Coast, interacting with remnants of Tropical Storm Rachel, which will soon turn northeast and move towards the California/Mexico Border coastline over the next couple of days.
In addition the the increasing gusty winds, widespread light to moderate rainfall is likely late Saturday-Tuesday, with highest confidence for Sunday-Monday. There is a 10% chance of thunderstorms during the same timeframe. While rain/thunderstorms are possible anywhere, highest chances exist south of Point Conception.
As this is a complex and evolving situation, please continue to monitor the forecast.
08/941 AM.
The Coastal Flood Advisories continue into Tuesday afternoon. Southerly swells, including from Tropical Storm Rachel, will continue to impact the LA/VTA coastline. 160-190 degrees at 12 seconds will pose the most risk from Malibu to Ventura through Friday. The Long Beach area is also at a relatively higher risk due to vulnerabilities from previous coastal events. The morning and evening high tides will remain similar in height at 6.5-7.0 ft through tonight, with a 0.3 ft reduction in the evening tides on Friday.
Meanwhile, Tropical Storm Rachel is expected to turn northeast, likely making landfall on Saturday night through Sunday somewhere in northern Baja California or in the vicinity of the Mexico- United States border (potentially as a post-tropical system).
As for impacts, deviations in the final track could influence the magnitude of impacts for the area. If Rachel takes a more northerly track, the combination of the increased wind wave and lower SFC pressure would result in higher tides, which are already expected to increase to 7.0 to 7.5 feet (1 to 1.5 feet higher than astronomical tides) over the weekend.
As of now, the most reasonable outcome for LA/Ventura and Catalina Island is flooding of sea-water over beach roads and paths, as well as significant beach erosion, with isolated damage possible. The time window for most concern is Sunday, especially during the morning high tide.
For the Central Coast, high surf advisories will likely be needed Saturday through Monday. In addition, there is a moderate risk for some beach erosion and isolated, minor coastal flooding.
Coastal flooding concerns will continue into early next week Refer to CFWLOX for more details and please continue to monitor the forecast for the latest information.
Ca, Extreme Heat Warning in effect until 8 PM PDT this evening for zones 38-87-88-349>358-362-366>375-548-550. (See LAXNPWLOX). Coastal Flood Advisory in effect until 2 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Heat Advisory in effect until 8 PM PDT this evening for zones 340>348. (See LAXNPWLOX). PZ, NONE.
