07/905 AM.
A major and long lasting heat wave will persist through at least Thursday with dangerously high temperatures, though some cooling is expected near the coast. 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), 07/221 PM.
Synoptically, a 590 dam High extends from the Bay area through Mexico to our southeast. By Saturday, that High has moved east to Texas and a large trough will drop down the California coast, allowing the track of the tropical system to our southwest (Rachel) to turn towards the Baja peninsula. While the tropical will remain well south of the CWA, peripheral moisture and swells could bring a rainy weekend with coastal impacts.
The high pressure overhead will slowly weaken today and Thursday. By Friday it will be nothing more than a weak ridge. At the surface, onshore flow will increase each day except across the Central Coast. This combination of lowering heights and increasing onshore flow will kick off a three-day cooling trend, especially on Friday.
The cooling today will not be enough to eliminate the heat risk with mostly 90s across the coasts, and 98 to 105 in the valleys. It only has reached 96 so far today in downtown LA, so the consecutive triple digit day streak will likely end at 5.
Most areas will cool 2 to 4 degrees on Thursday. More noticeable cooling arrives on Friday; 4 to 8 degrees across the board. This will be enough to finally eliminate the heat risk.
Some low clouds will likely develop south of Pt Conception and there will be more low clouds across the Central Coast as well. This increasing trend will continue Friday morning where most coastal areas will wake up to low clouds and patchy fog.
The forecast for Saturday will depend on the exact track of Rachel, but it is likely to bring increasing cloudiness and continued cooling. Light rain could arrive as early as Saturday morning in LA and Ventura Counties, but more realistically it will not arrive until Saturday night into Sunday morning.
(Sun-Wed), 07/231 PM.
An early season cold upper low moves out of British Columbia and into the west coast, developing into a large trof and by Sunday. Onshore flow will increase and there will be a much more robust marine layer stratus layer across the coasts and some valleys. Max temps will drop an additional 4 to 8 degrees on Sunday. Sunday's max temps across the coasts and valleys south of Pt Conception will only be in the 70s and the Central Coast will see nothing but 60s.
The most likely period of rain from Rachel's moisture is 9am Sunday through 9am Monday in LA and Ventura County. Some light rain could extend into Santa BArbara and SLO Counties as well.
An upper low will move over the Central Coast during the day on Monday. Hgts could fall as low as 562 dam. This low and the remnant moisture will bring a chance of rain showers and a 5-10% chance of TSTMs to the entire area during the day.
While SLO and SBA counties will likely see less than a tenth of an inch of rain, Ventura and LA Counties amounts will be more like 0.5" The most rain is expected in the eastern portion of the LA County mountains, which could get up to 2 inches of rain. The upper low, the clouds and the rain will bring another 3 or 4 degrees of cooling to most areas and highs will only range from the upper 60s to lower 70s. Little change across the Central Coast.
Rain should end by Tuesday and decreasing clouds and warming are expected both Tuesday and Wednesday, and downtown LA should be in the mid-70s by then.
07/2305z.
At 2230Z at KLAX, the marine layer was 600 feet deep. The top of the inversion was 2100 feet with a temperature of 30 degrees Celsius.
For 00Z TAF package, high confidence in CAVU conditions for KPRB, KBUR, KVNY, KWJF and KPMD.
For KSMX and KSBA, moderate confidence in 00Z TAFs with timing of flight category changes +/- 2 hours of current forecasts.
For KSBA, KOXR, KCMA, KSMO, KLAX and KLGB, low confidence in 00Z TAFs as there is a 50% chance that CIG/VSBY restrictions do not develop.
KLAX, Low to moderate confidence in 00Z TAF. There is a 50% chance that CIG/VSBY restrictions do not develop. If CIG/VSBY restrictions do develop, timing of flight category changes could be +/- 3 hours of current forecasts with an equal chance of IFR or LIFR conditions. No significant easterly wind component is expected.
KBUR, High confidence in 00Z TAF as CAVU conditions are expected through the period.
07/225 PM.
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. Additionally, a short lived SCA has been issued for the northern portion of the outer waters (north of Point Sal) this afternoon through late evening for increasing northwest winds. 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 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 the systems final track which will determine the exact details. The most recent guidance has shifted to the south which keeps Rachel well to the south which would limit impacts. However, strong SCA W-SW winds are still a certainity as the system interacts with the trough with a 20% chance of GALES especially across the inner waters. Showers will linger into Monday and Tuesday across the coastal waters. 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.
07/225 PM.
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 at 12 seconds will pose the most risk from Malibu to Ventura Thursday and Friday. Long Beach area is also at a relatively higher risk due to vulnerabilities from previous coastal events. High tides will remain similar in height at 6.5-7.0 ft through Thursday and with a 0.3 ft reduction in the evening tides on Friday.
Hurricane Rachel is expected to turn northeast and will pick up in movement speed likely making landfall 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 become more clear likely in a day or two as the system turns to the northeast. Deviations in the final track could influence the magnitude of impacts for the area. The most reasonable solution at this time will likely have considerable to significant impacts especially for vulnerable beaches such as Long Beach. The time window for most concern is Sunday especially during the morning high tide.
The tide is expected to be 7.5 ft (+/- 0.5 ft). If Rachel takes a more northerly track, the combination of the increased wind wave and lower SFC pressure would result in higher tides- vice versa.
For the Central Coast, high surf advisories will 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 Thursday 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 Thursday for zones 340>348. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Thursday for zone 670. (See LAXMWWLOX).
