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-Fri), 08/138 PM.
Overall, 12Z models in good synoptic agreement through the short term period. At upper levels, high pressure will peak over the area on Wednesday, then weaken Thursday/Friday. At the surface, weak diurnal gradients will prevail tonight/Wednesday with strengthen onshore gradients Thursday/Friday.
Forecast-wise, main concern in the short term period will be the heat. With upper level high pressure peaking in strength and weak offshore pressure gradients in the morning, Wednesday will be a very hot day with highs ranging from the mid 80s to lower 90s at the beaches to up to 108 degrees across interior sections. On Thursday, the upper level high weakens and pressure gradients are onshore all day, so temperatures will be several degrees cooler (but still very warm). Overnight low temperatures through Thursday night will only drop into the mid 60s to mid 70s. Unfortunately with these temperatures, surface dew points are expected to be in the mid 60s to mid 70s (thanks to Marie), making conditions VERY oppressive. Based on Heat Risk grids (combining high/low temperatures as well as humidity), there will be widespread MAJOR HEAT RISK and localized pockets of EXTREME HEAT RISK Wednesday through Thursday. Therefore, the HEAT ADVISORIES have been upgraded to EXTREME HEAT WARNINGS for Wednesday through Thursday. On Friday, highs are expected to cool at least 4-8 degrees for all areas which should greatly limit any concerning heat risk across the area.
Our secondary concern is continued shower/thunderstorm activity moving across the area this afternoon. Showers and isolated thunderstorms are expected to continue to move northward across the area this afternoon with all areas having a chance of showers and thunderstorms. There will be plenty of lightning, but rainfall amounts (based on what has already fallen) are not expected to be too significant at this time. So, hydrologic issues are expected to be minimal. This activity will dissipate by early this evening. On Wednesday, there will be enough lingering moisture/instability over the Ventura/LA mountains to warrant a slight chance of showers and thunderstorms Thursday afternoon across the higher terrain.
Other than the heat and convective activity, the excitement levels will remain low. With the weak offshore pressure gradients Wednesday morning, there'll be some offshore winds. However, upper support is minimal and any offshore winds are expected to remain well below advisory levels. However, I would not be surprised to see some locally gusty conditions across the Santa Lucia Range Wednesday morning.
(Sat-Tue), 08/138 PM.
For the extended, 12Z models continue to exhibit good synoptic agreement through the extended period. At upper levels, the ridge will remain flat through Monday, then may start to strengthen a bit on Tuesday. At the surface, weak to moderate onshore pressure gradients are expected.
Forecast-wise, the above pattern will result in rather benign weather through the period. Skies should remain mostly clear for most areas with some stratus/fog likely returning to the coastal plain during the night/morning hours. As for temperatures, there will be minor day-to-day fluctuations in temperatures, but the area will be about 3-6 degrees below normal. With atmospheric moisture also decreasing, conditions will be rather comfortable and no heat issues are expected.
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.
08/128 PM.
There continues to be a slight chance of thunderstorms over the waters through this evening, with a cluster of storms currently moving to the northeast through large portions of the waters south of Point Sal. 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.
08/123 PM.
There is a slight chance of thunderstorms across all beaches into this evening. Any thunderstorm that forms could produce local gusty and erratic winds, brief heavy downpours, and dangerous cloud-to-ground lightning. Low but nonzero thunderstorm chances exist Wednesday.
A south swell from post tropical cyclone Marie is subsiding, but continued coastal impacts are likely through at least tonight. High surf will continue through tonight, gradually decreasing as the southerly swell decreases. Highest surf is still expected across south facing coasts across LA/Ventura Counties, esepcailly near Zuma Beach and the Long Beach coastline. Very strong and dangerous rip currents will continue as well.
Moderate coastal flooding has occurred and minor to locally moderate coastal flooding will continue through Thursday around evening high tides for south facing shores as the swell decreases, but tides remain very high. The actual observed tides have been running about 6 inches above predictions, with the evening tides near or exceeding 7 feet.
Expect continued beach erosion, flooded sandy beach areas, bike paths, and parking lots, as well as low-lying roads. Some areas that may continue to see impacts are: the Alamitos Peninsula in Long Beach, Avalon on Catalina Island, and Oxnard to Malibu (including the Pacific Coast Highway near Point Mugu).
Beach Hazards Statements (BHS) have been issued for the beaches of Los Angeles and Ventura Counties following the expiration of the Coastal Flood Advisories due to the very high evening tides Wednesday and Thursday. There will be some lingering southerly swell into Wednesday.
Ca, Extreme Heat Warning in effect from 8 AM Wednesday to 8 PM PDT Thursday for zones 38-87-88-340>358-362-366>375-548. (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 from 11 PM PDT this evening through Thursday evening for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect until 11 PM PDT this evening for zones 340-346. (See LAXCFWLOX). Beach Hazards Statement in effect through Thursday evening for zones 349-350. (See LAXCFWLOX). Heat Advisory in effect until 8 AM PDT Wednesday for zones 362-366>373-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 9 PM PDT this evening for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Thursday for zones 673-676. (See LAXMWWLOX).
