Marine Weather and Tide Forecast for Hacienda Heights, CA

.SHORT TERM (TDY-SAT)...12/846 PM.

***UPDATE***

Highs climbed into the 80s and 90s for the valleys, coastal plains, and much of the coasts under clear skies and easterly winds. Southern Ventura County reached into the low to mid 90s in spots, crushing a few daily records set back in 2015. Tomorrow, expecting similar temperatures with a few degrees of cooling near the coasts. Highs were warmed for Friday to closer reflect today's high temperatures.

Sub-advisory level northeast to east winds are expected over higher terrain tonight, becoming more northerly into Friday morning. Still, the offshore winds look weaker than this morning, so expecting a bit cooler temperatures near the coasts. High pressure weakens over the weekend, leading to a slight cool down.
Otherwise, the forecast looks on track.

***From Previous Discussion***

Overall, 12Z models in good synoptic agreement through the short term period. At upper levels, the high, just offshore, peaks in strength today then weakens gradually Friday/Saturday before restrengthening on Sunday. Near the surface, weak offshore flow prevails through Friday morning, switches weakly onshore Friday afternoon through Saturday before shifting back weakly offshore on Sunday.

Forecast-wise for the short term, main focus will remain on temperatures. As expected, today has been a very warm day, topping out in the mid 80s to mid 90s. For Friday, the return of the weak onshore flow in the afternoon will allow for some slight coastal cooling, but keep temperatures near persistence across inland areas. So, high temperatures on Friday will still be warm enough (15-25 degrees above normal) to warrant heat products. So, will keep the HEAT ADVISORIES in effect for the coasts and coastal valleys through Friday afternoon. On Saturday, all areas will experience a cooling trend with coastal/valley areas cooling as much as 5-10 degrees. However on Sunday, as the upper level high begins to strengthen again and weak offshore surface gradients develop, temperatures will increase yet again, generally into the 80s to lower 90s. HEAT ADVISORIES could be needed on Sunday for some coastal valley areas.

Other than temperatures, no significant issues are expected through the period. The weak offshore pressure gradients today through Friday morning and again on Sunday will generate some gusty northeasterly winds. However without any noticeable upper level support, will expect winds to remain below advisory levels.
As for clouds, mostly clear will be likely for most areas through the period. However, on Saturday and Sunday, there may be some night and morning stratus/fog along the coastal plain (mainly LA county coast and the Central Coast).

.LONG TERM (SUN-WED)...12/123 PM.

For the extended, 12Z models continue to remain in good synoptic agreement through the period. At upper levels, an extraordinarily strong high pressure will build right over the area. At the surface, there is the potential for weak diurnal flow (best case scenario based on the GFS) or weak offshore flow (worst case scenario based on the ECMWF). Either way, nothing in the latest guidance indicates anything but an extremely impressive heat wave next week.

Details that make this heat event very impressive:

1. 500 mb heights are forecast to range between 590 and 595 DM which would be the highest March H5 heights since 1948.

2. 1000-500 mb thickness are forecast to peak in the 580 to 584 DM range. Based on the 25+ year history of TEMP STUDY, the highest thicknesses recorded in March are 571 DM.

3. The Extreme Forecast Index (EFI) indicates values between 0.8 and 1.0 for both Maximum and Minimum temperatures, signifying a very usual or extreme event.

4. If the weak offshore flow, forecasted by the ECMWF, pans out then temperatures west of the mountains could be higher than currently forecast.

5. Based on current forecasts, both daily and monthly March temperatures records could fall for most climate sites.

At this time, there is high confidence in the need for HEAT ADVISORIES for most areas next Tuesday through Thursday, and possibly as early as Monday for some areas. Additionally, there is a 40-50% chance that EXCESSIVE HEAT WARNINGs may be needed for some areas Tuesday through Thursday.

Given the unprecedented length and magnitude of this extreme heat wave, heat stress will be a real threat each day, especially in areas that aren't used to the heat, like the coastal areas, where people may not have methods to cool off their homes. Try to complete outdoor activities early in the day or in the evening, and don't leave people or pets in cars.

As for any rain chances, deterministic and ensembles do not indicate any chances for significant rain through the 28th.

AVIATION
13/0505Z.

At 0356Z at KLAX, there was no marine layer. There was a surfaced based inversion with a top at 1100 ft and a temperature of 29 C.

High confidence in VFR TAFs and moderate confidence in winds.

Light LLWS is possible through 13/18Z. There is a 20% percent chance northeast winds 15-20 kt briefly surface at KSBP thru aforementioned time period.

KLAX...High confidence VFR TAF. No significant east wind component expected.

KBUR...High confidence VFR TAF.

MARINE
12/749 PM.

Moderate to high confidence in Small Craft Advisory (SCA) level northwest to north winds up to 25 kt through tonight, increasing to 20-30 knots tomorrow and impacting the Outer Waters through at least Sunday night. There is a 50% chance of low end Gale Force winds (roughly 35 knots) across the waters beyond 30 NM from shore Friday evening through late Saturday night, with a Gale Watch in effect. Seas will increase during this period, with moderate confidence in seas reaching at least 10 feet across the outer waters. Conditions are likely to improve early next week, with relatively small seas expected.

Small Craft Advisory (SCA) level winds will affect the Inner Waters along the Central Coast during the afternoon to evening hours Friday and Saturday, with a 30% chance of SCA winds Sunday afternoon and evening.

Inside the Southern California Bight, conditions are expected to remain below SCA levels for the foreseeable future, except for very localized SCA level winds across the far northwestern portion of the Santa Barbara Channel Saturday.

LOX WATCHES/WARNINGS/ADVISORIES
CA...Heat Advisory remains in effect until 8 PM PDT Friday for zones 88-340>342-346>352-354>358-362-366>375-548. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM Friday to 3 AM PDT Saturday for zone 645. (See LAXMWWLOX).
Small Craft Advisory in effect until 9 PM PDT Friday for zones 670-673. (See LAXMWWLOX).
Gale Watch in effect from Friday evening through late Saturday night for zones 670-673. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Saturday for zone 676. (See LAXMWWLOX).
Gale Watch in effect from late Friday night through late Saturday night for zone 676. (See LAXMWWLOX).