07/215 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. Friday into Sunday, temperatures will trend cooler each day and there will be an increasing chance of showers and thunderstorms due to moisture from Hurricane Rachel.
(tdy-Fri), 07/1204 AM.
The big dome of hot high pressure will slowly weaken today and Thursday. By Friday it will be nothing more than a weak 582 dam ridge. At the sfc the onshore flow will increase each day (except across the Central Coast today where offshore flow will increase).
This combination of lowering hgts and increasing onshore flow will kick off a three day cooling trend esp on Thu and Fri. Today the csts and portions of the vlys south of Pt Conception will see about 4 degrees of cooling. The increase in offshore flow across the Central Coast will lead to 4 to 8 degrees of warming today. The cooling will not be enough to eliminate the heat risk with mostly 90s across the coasts and 98 to 105 in the vlys. There is only a 30 percent chc of DTLA reaching a temp of 100 or more degrees today and the new October for consecutive triple digit days will likely end at 5.
Most areas will cool 2 to 4 degrees on Thursday. Noticeable cooling arrives on Friday, look for 4 to 8 degrees of cooling across the board. This is enough cooling to eliminate the heat risk.
There will not be too much marine layer clouds this morning, just some around the SLO and western SBA beaches accompanied by dense fog. 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.
(Sat-Tue), 07/230 AM.
A dramatic switch in the weather will occur over the weekend as a early season cold upper low moves out of British Columbia and into the west coast. It will develop into the large trof and by Sunday hgt could drop to 565 dam. Onshore flow increases as there will be a much more robust marine layer stratus layer across the csts and some vlys. Max temps will drop 5 to 10 degrees on Saturday and an additional 4 to 8 degrees on Sunday. Sunday's max temps across the csts/vlys south of Pt Conception will only be in the 70s and the Central Coast will see nothing but 60s. Sunday's max temps will be 3 to 6 locally 8 degrees blo normal.
There is also a chance that moisture from Rachel's remnants will interact with the trof and bring some showers to LA county with a better chc from the OC southward.
On Monday the trof will pinch off an upper low that will move over the Central Coast during the day. Hgts could fall as low as 562 dam. This low and the remnant moisture will bring a chc of rain showers and a 5-10% chance of TSTMs to the entire area during the day on Monday. While SLO/SBA/VTA counties will likely see less than a tenth of an inch of rain, LA county (esp the eastern portion) could see up to .75 inches of rain. The upper low, the clouds and the rain will bring another 3 or 4 degrees of cooling to most areas (little change across the Central Coast) and highs will only range from the upper 60s to lower 70s.
The upper low and moisture should pull out of the region overnight Monday and area should be dry and about 4 degrees warmer (still 5 to 10 degrees blo normal)
07/0915z.
At 0832Z at KLAX, there was a surface-based inversion. The top of the inversion was 2500 feet with a temperature of 30 C.
Moderate confidence in TAFs for KSBP and KSMX. Vis may vary from 1/4SM to 1SM through 15Z. IFR conds are possible 14Z-16Z. VFR conds could arrive as late as 17Z.
High confidence in the remainder of TAFs.
KLAX, High confidence in CAVU TAF.No significant easterly wind component is anticipated.
KBUR, High confidence in CAVU TAF.
07/230 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. 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.
Increasing west to northwest winds and seas (10+ foot off Central Coast) are likely this weekend through at least Monday. Additionally, remnant moisture from current Hurricane Rachel will bring a chance of showers and a very small chance of thunderstorms to the waters late this weekend into early next week, best chances south of Point Conception.
07/230 AM.
Southerly swell from Hurricane Rachel will impact the Los Angeles and Ventura Counties coastline including Catalina Island through at least Saturday. A Coastal Flood Advisory is in effect through Friday.
The swell direction will start to turn from the south-southeast (150-160) to more southerly (170-190) over the course of the day through Friday. Unlike previous events, morning and evening high tides will be similar in height ranging 6.5 to 7.0 ft. Coastal flooding impacts are anticipated to be greatest for Long Beach (especially Alamitos Peninsula), Catalina Island (while the swell is SSE), and the Malibu/Zuma Beach coast.
Saturday into early next week, tides will be very high (7+ feet) and a combination of multiple longer and shorter period swells from the south and west are expected to impact our coastline over the weekend into at least early next week. Plenty of uncertainty exists regarding the timing and magnitudes of these swells, thus there is lots of uncertainty in exact coastal flooding and surf impacts. However, there is a risk for significant impacts. Additionally, there is a very small chance of showers and thunderstorms Sunday into Monday.
Please continue to monitor the forecast.
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). Beach Hazards Statement in effect until 6 AM PDT early this morning for zones 87-354-362-366. (See LAXCFWLOX). Coastal Flood Advisory in effect from 6 AM this morning to 11 PM PDT Friday for zones 87-354-362-366. (See LAXCFWLOX). Heat Advisory in effect from 10 AM this morning to 8 PM PDT Thursday for zones 340-346. (See LAXNPWLOX). Heat Advisory in effect until 8 PM PDT Thursday for zones 341>345-347-348. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Thursday for zone 670. (See LAXMWWLOX).
