07/601 PM.
A significant southerly swell will cause hazardous surf conditions at the beaches through at least Tuesday. Isolated showers will continue at times through Tuesday. The combination of increasing heat and humidity across the area will cause moderate to major impacts, focused over the coasts and valleys Tuesday through at least Thursday.
(Mon-Thu), 07/806 PM.
***UPDATE***
Here are the top ten rainfall totals for this event:
PRELIMINARY PRECIPITATION TOTALS
.TOP RAINFALL AMOUNTS FROM ALL LOCAL AREAS OPIDS CAMP (LA COUNTY). . . . . , 1.86 STUNT RANCH (LA COUNTY). . . . . .. 1.58 CHILAO SOUTH (LA COUNTY). . . . . . 1.57 BEL AIR (LA COUNTY). . . . . . .. 1.56 CHILAO (LA COUNTY). . . . . . , 1.56 MONTE NIDO (LA COUNTY). . . . . , 1.53 BURBANK (KBUR) (LA COUNTY). . . . , 1.46 SEPULVEDA CYN AT MULH (LA COUNTY). . . 1.45 BEVERLY HILLS (LA COUNTY). . . . . 1.42 CRYSTAL LAKE (LA COUNTY). . . . . . 1.41
For more totals see RRMLOX: forecast.weather.gov/product.php?site=lox&issuedby=LOX&product=RRM
Isolated showers will linger across LA county through the evening. For Tuesday, 10-25% chance of showers and thunderstorms across all four counties mainly focused along the Central Coast. For Wednesday and Thursday, a slight chance of showers and thunderstorms (10-15%) will stay confined over the local mountains - Lockwood valley and eastern San Gabriels. 5% chance or less across rest of the interior.
One key note I want to emphasis is that humidity levels will be rather extreme across the LA Basin for the upcoming heat focused Tuesday through Thursday. Wednesday will have the highest risk for heat illness. Some model projections such as the ECWMF has dewpoint values in excess of 75 degrees with less cloud cover which would push the LA Basin area into the WARNING category. However, there is still quite the spread in dewpoints and cloud cover thus will stay with heat advisories for now (20-30% chc of an upgrade to an Extreme Heat Warning). Stay tuned for future updates.
***From Previous Discussion***
Now that the main rain event from Tropical System Marie is behind us, the focus of the forecast pivots to the the upcoming heat event. While remnants of Marie will remain well off the California Coast over the next few days, a ridge of high pressure will build into the region from the east over the next several days. Temperatures will trend upwards each day through Wednesday, when 500 mb heights and the light offshore winds will peak. For most areas Wednesday will be by far the warmest day of the event, most noticeably along the Central Coast including Santa Maria and San Luis Obispo, except the Santa Barbara South Coast may see the warmest temperatures on Thursday due to an increase in Sundowner winds in the area.
Heat Advisories are in effect Tuesday through Thursday for Los Angeles County beaches and coastal valleys, and the Santa Monica Mountains. Wednesday Heat Advisories are expanded to include the Ventura County coasts and valleys, the Santa Clarita Valley, and all of Santa Barbara and San Luis Obispo Counties. Widespread highs will peak in the 90s (including near some coasts) to low 100s. Due to Marie's influence on the area, humidity will be elevated which will significantly increase the HeatRisk and discomfort. The moisture will impact overnight low temperatures, which will remain very warm (widespread 70s with even some 80s in the foothills). Mid and high cloud coverage will serve to moderate heat impacts at times, and the overall event will be relatively short compared to other heatwaves we have seen so far this summer. This heat may feel comparable or even slightly worse to recent heat waves, especially near the coast. Those working or recreating outdoors as well as those without air conditioning are advised to follow the forecast, stay hydrated, and seek cooling centers when possible. There is around a 20-30 percent chance of the Heat Advisories being upgraded to Extreme Heat Warnings on Wednesday. This will depend some on the anticipated cloud coverage. The coastal areas along the Central Coast are of particular concern on Wednesday, where temperatures may reach 100 degrees or higher for some locations (20+ degrees above normal).
Tropical Storm Marie is currently centered 750 miles southwest of Los Angeles, continuing its northwest movement well offshore of southern California. Even so, moisture and south swells remain in the area. There is an ongoing, significant hazard across south facing beaches, with strong and potentially deadly rip currents (see coastal hazards for details). As for more rain, there is a slight chance (5-15%) of thunderstorms focused over LA and Ventura County through this afternoon, and then tomorrow focused over Ventura Santa Barbara Counties and the Central Coast (and coastal waters). This is due to the very high PWATs brought into the region by Marie, combined with any sources of lift. Minor scattered shower are possible through Tuesday. Then by Wednesday, shower and thunderstorm activity will likely become confined to the highest mountains as the strengthening ridge caps and slightly dries out mid-levels of the atmosphere.
(Fri-Mon), 07/226 PM.
There is the potential for Heat Advisories to be extended on Friday, however there is high uncertainty for this time period. Ridging is favored to continue for the area on Friday, but 500 mb heights will not be as high as previously, and onshore flow will be stronger thus increasing the cooling seabreeze. By the weekend, near normal temperatures appear likely. Troughing off the coast may reestablish at times, keeping the door open for additional tropical moisture to shuttle into southwest California.
08/0112z.
At 2355Z at KLAX, there was no marine layer. A surface inversion had a top near 1800 feet, with a temperature of 28 degrees C.
Low to moderate confidence in the Central Coast sites where the marine layer coverage is lower certainty. Dense fog is likely at KSMX (60%) and possible (20%) at KSBP. The timing of low CIGs and VSBY could differ +/- 2 hrs from TAF times. In addition, there is a slight chance of showers and thunderstorms along the Central Coast, and portions of Santa Barbara, Ventura and LA Counties 12Z Tue through 00Z Wed. CIGs and especially VSBY could lower during any storms that occur, with a chance of brief heavy showers.
KLAX, Moderate confidence in the 00Z TAF. Stratus CIGs are not expected but there is a slight chance of -SHRA (and a non-zero chance of -TSRA) between 12Z to 00Z. Any showers could produce locally gusty winds and brief moderate to heavy rain. No significant east wind component expected.
KBUR, Moderate confidence in the 00Z TAF. There is a slight chance of -SHRA (and a non-zero chance of -TSRA) between 12Z to 00Z. Any showers could produce locally gusty winds and brief moderate to heavy rain.
07/805 PM.
For the waters south of the Channel Islands, there is a slight chance of thunderstorms through this evening. Any thunderstorm that storms could produce local gusty and erratic Gale Force winds and seas, brief heavy downpours, and dangerous cloud-to- surface lightning. An additional slight chance of thunderstorms will affect portions of the waters Tuesday, mainly in the western Santa Barbara Channel and northward.
For the Outer Waters, below Small Craft Advisory (SCA) level winds and seas are expected into Wednesday, except for local advisory level gusts around Point Conception each afternoon and evening. Wednesday night through Friday, SCA winds are likely much of the time, especially over the southern zones near and south of Point Conception.
For the Inner Waters north of Point Sal, there is a 60% chance of SCA winds Thursday afternoon through Friday.
For the Inner Waters south of Point Conception, localized areas of borderline SCA winds are likely Tuesday afternoon and evening, nearshore along the LA County coast and through the San Pedro Channel. The focus for SCA winds will shift to the western Santa Barbara Channel Thursday into the weekend.
A south swell is impacting the area, although beginning to subside. This swell may still cause increased currents and surges in vulnerable harbors. Breaking waves may impact some south facing harbor entrances, particularly for Ventura and Los Angeles Counties.
07/726 PM.
There is a slight chance of thunderstorms across the Los Angeles County beaches through this evening. Any thunderstorm that forms could produce local gusty and erratic winds and seas, brief heavy downpours, and dangerous cloud-to- surface lightning. Additional thunderstorm chances are expected early Tuesday morning through the afternoon hours, affecting mainly the Central Coast and Santa Barbara South Coast, but with a non-zero chance further south.
A south swell from tropical storm Marie is beginning to subside, but with continued coastal impacts likely through Tuesday. High surf will affect south- facing beaches of Ventura and Los Angeles counties, peaking at 4-7 feet with local sets to 8 feet through Tuesday afternoon. Very strong rip currents will continue as well. The highest surf is along Zuma Beach and the Long Beach area. HIGH SURF ADVISORIES remain in place for Los Angeles and Ventura Counties, with BEACH HAZARDS STATEMENTS in effect for Santa Barbara and San Luis Obispo Counties.
Moderate coastal flooding has occurred and will continue around high tides for south facing shores. The actual observed tides have been running about 6 inches above predictions, with the evening tides likely near or exceeding 7 feet. As the surf begins to diminish, the coastal flooding will subside somewhat.
Expect beach erosion, flooded sandy beach areas, bike paths, and parking lots, as well as low-lying roads. Of particular concern will be the Alamitos Peninsula area in Long Beach where coastal flooding will potentially cause local damage to structures near times of high tide. Other areas of concern the next couple of days include Catalina Island, and Oxnard to Malibu (including the Pacific Coast Highway near Point Mugu). COASTAL FLOOD ADVISORIES remain in effect for Los Angeles and Ventura Counties where the best combination of tides and waves will occur, but Santa Barbara and San Luis Obispo Counties could also see some isolated issues.
Ca, Heat Advisory in effect from 10 AM Wednesday to 8 PM PDT Thursday for zones 38-88-340>358-374-375. (See LAXNPWLOX). Coastal Flood Advisory in effect until 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). High Surf Advisory in effect until 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect through Tuesday evening for zones 340-346-349-350. (See LAXCFWLOX). Heat Advisory in effect from 10 AM Tuesday to 8 PM PDT Thursday for zones 362-366>373-548. (See LAXNPWLOX). PZ, NONE.
