08/231 AM.
A significant southerly swell will bring hazardous surf conditions to 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.
(tdy-Thu), 08/830 AM.
***UPDATE***
Latest satellite and surface observations indicate partly cloudy skies across the area as moisture from Marie continues to stream across the area. Radar indicates some showers/isolated thunderstorms over the southern Inner Waters. No significant winds are currently observed.
For the immediate short term, two main issues will be rain chances and the beginning of the heat. With respect to rain chances, current radar indicate scattered showers/isolated thunderstorms over the coastal waters. With plenty of Marie moisture over the area, there will be threat of showers and thunderstorms for most areas through this afternoon. With any shower/thunderstorm activity, brief moderate/heavy showers will be possible. The second concern will be the beginning of the heat. Weak offshore pressure gradients this morning will limit the sea breeze effect and allow temperatures to climb today. The heat generated by this will be exacerbated by the increased humidity due to Marie moisture. So, today will feel quite uncomfortable across the area. Based on current Heat Risk grids, advisory-level heat concerns are likely across the LA Basin. So, will keep HEAT ADVISORIES in effect for the LA Basin today. Although heat products will not be in effect today for other areas, it still will be quite warm and uncomfortable and folks should exercise caution with any outdoor activities today.
For the morning update, did tweak the shower/thunderstorm chances for today. Otherwise, forecast looks good for the immediate short term. For the afternoon forecast suite, attention will remain on heat potential for most areas on Wednesday/Thursday.
***From Previous Discussion***
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
PWATs will reach 1.7 inches today as moisture from former hurricane Marie continues to feed into Srn CA. This will lead to a 10-20% chance of showers and thunderstorms across all four counties today. For Wednesday, a slight chance of showers and thunderstorms (10-15%) will continue over the northern VTA county mtns. There will be a 5% chance will over the rest of the mtn areas.
The main weather story for the next three days will be the heat and humidity. An upper high will migrate to the west and will end up over Needles by Thursday. Hgts will rise from 588 dam Monday evening to 596 dam Thursday. At the sfc there will be weak offshore flow this morning and Wednesday morning with only very weak onshore flow in the afternoon. Not enough offshore flow to create much of any canyon winds but enough to deprive the area of the cooling sea breeze. Thursday will see a some onshore trends which will serve to cool the csts some but the interior will continue to sizzle. The big additional problem will be the humidity which will be much higher than normal as PWATs will be near 1.5" which is .86" greater than normal.
The combination of hotter than normal temps and much higher than normal humidities has prompted the issuance of heat advisories for the Los Angeles County beaches and coastal valleys, and the Santa Monica Mountains today through Thursday. On Wednesday additional Heat Advisories go into effect for the Ventura County coasts and valleys, the Santa Clarita Valley, and all of Santa Barbara and San Luis Obispo Counties and are valid through Thursday evening.
There is 20-30 percent chc that humidities will rise to levels high enough to trigger heat warnings on Wednesday.
In addition to the daytime humidities the moisture will also keep overnight low temperatures well above normal with widespread 70s with even some 80s in the foothills).
The Central Coast will not be immune from this event as offshore flow on Wednesday will drive some temperatures all the way to 100 to 102 degrees and most areas will end up 20 degrees or more above normal.
(Fri-Mon), 08/231 AM.
Hgts should fall to about 592 dam on Friday while at the same time onshore flow increases both to the N and E. This should lead to 3 to 6 degrees of cooling for almost all of the area. PWATs fall as well but will still be above normal. If all of this comes to fruition there will be no need for any heat products. There is, however, a 20 percent chc that this cooling may be slower to develop and there will be a need for one more day of heat headlines.
The ridge flattens out over the weekend and onshore flow continues. Look for 3 to 6 degrees of cooling on Saturday which should bring most temps to a few degrees blo normal. Sunday's temps will be similar to Saturdays. PWATs should drop down to normal as well.
Onshore flow weakens some on Monday and this should lead to 1 or 2 degrees of warming.
08/1729z.
At 1641Z at KLAX, there was no marine layer. A surface inversion had a top near 1500 feet, with a temperature of 28 degrees C.
There is a slight chance of showers and thunderstorms continuing through 00Z for all sites, but there is currently a cluster of storms in LA County as well as west of the coast, heading into LA/Ventura Counties.
Low to moderate confidence in the Central Coast sites. There is a 40 percent chance of no low clouds at KSMX and a 40 percent chance of LIFR conds at KSBP 06Z-17Z.
Good confidence in no low clouds for the rest of the sites.
KLAX, Good confidence in TAF. -TSRA will impact the terminal through around 19Z-20Z, with a slight chance through 00Z. Any showers could produce locally gusty winds and brief moderate to heavy rain. No significant east wind component expected, although significant wind shifts may occur with any TS.
KBUR, Good confidence in TAF. Showers are likely to pass over the area through the afternoon. There is a 30 percent chance of -TSRA through 20Z, with a slight chance through 00Z. Any showers could produce locally gusty winds and brief moderate to heavy rain. Significant wind shifts may occur with any TS.
08/823 AM.
There will be a slight chance of thunderstorms over portions of the waters through today, with a cluster of storms currently moving to the northeast through the waters south of the Santa Barbara Channel. Smaller yet nonzero chances exist Wednesday.
Good confidence in winds and seas increasing to Small Craft Advisory (SCA) levels this afternoon focused south and west of Point Sal, with moderate confidence in winds increasing across all Outer Waters by Wednesday at the earliest. Winds and at times seas will likely exceed SCA levels into early next week.
Across the nearshore waters along the Central Coast, winds will locally reach SCA levels today and tomorrow, with more expansive gusty winds Thursday into early next week, with SCAs likely to be issued.
South of Point Conception, moderate confidence in SCA winds across the western half of the Santa Barbara Channel (locally eastern portions) each afternoon and evening into early next week. Thus, there is a 40-60% chance for SCAs to be issued each day, with highest chances today and again this weekend. Local SCA gusts will be possible each afternoon-evening across the Santa Monica Bay and San Pedro Channel into early next week with highest chances today.
The southerly swell that has impacted the coastal waters over the last few days will continue to gradually subside through tonight and tomorrow.
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 this evening for zones 87-354-362-366. (See LAXCFWLOX). High Surf Advisory in effect until 11 PM PDT this evening for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect through this evening for zones 340-346-349-350. (See LAXCFWLOX). Heat Advisory in effect until 8 PM PDT Thursday for zones 362-366>373-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 9 PM PDT this evening for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to 9 AM PDT Wednesday for zones 673-676. (See LAXMWWLOX).
