textproduct: Los Angeles

SYNOPSIS

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.

LONG TERM (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.

AVIATION

08/1240Z.

At 0832Z at KLAX, the marine layer was 500 feet deep. The top of the inversion was 1100 feet with a temperature of 29 C.

High confidence in CAVU conditions for KPRB, KBUR, KVNY, KWJF and KPMD.

Moderate confidence in TAFs for KSBP, KSMX, KSBA, KOXR and KCMA. Flight Cat changes could be off by +/- 90 minutes. Cigs could be off by +/- 200 ft. Vis may vary from 1/4SM to 1SM through 15Z.

Low confidence in TAFs for KSMO, KLAX and KLGB. There is a 40% chance of brief VLIFR CIG/VSBY through 16Z.

KLAX...Low confidence in TAF. There is a 30% chance of brief 1/2SM bkn002 conds through 16Z. IFR/LIFR conds could arrive as early as 10Z. No significant easterly wind component is expected.

KBUR...High confidence in CAVU TAF.

MARINE

08/241 AM.

Relatively quiet conditions expected across the coastal waters through Friday. 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.

The biggest concern this weekend will be potential impacts from the interaction between a trough coming down from the north and remnants of Hurricane Rachel focused across the waters adjacent to Los Angeles and Orange counties. There is still a considerable amount of uncertainty in regarding to Rachel's final track which will determine the exact details. The most recent guidance has shifted the track well to the south of the coastal waters, which would limit impacts. However, strong SCA W-SW winds are still a possibility as the system interacts with the trough with a 20% chance of GALES especially across the inner waters. Periods of light to moderate rain, with a 10% chance of thunderstorms will be possible across the waters as early as Saturday lasting into as late as Tuesday evening (highest confidence in Sunday/Monday timeframe). In addition, increasing west to northwest winds and seas (10+ foot) are expected across the outer waters this weekend into Monday.

Please continue to monitor the forecast.

BEACHES

08/241 AM.

The Coastal Flood Advisories have been extended into Tuesday afternoon. Southerly swells, including from Hurricane Rachel, will continue to impact the LA/VTA coastline. 180-190 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, Hurricane Rachel is expected to turn northeast and will pick up in movement speed (while wind speed weakens), likely making landfall on Sunday somewhere in northern Baja California or in the vicinity of the Mexico- United States border (as a post- tropical system). The exact track will likely become more clear in a day or two as the system turns to the northeast.

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.

LOX WATCHES/WARNINGS/ADVISORIES

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). Dense Fog Advisory in effect until 9 AM PDT this morning for zones 340-341-346-347. (See LAXNPWLOX). Heat Advisory in effect until 8 PM PDT this evening for zones 340>348. (See LAXNPWLOX). PZ...NONE.