Point Sal to Santa Cruz Island CA including San Miguel and Santa Rosa Islands Marine Forecast
|Tonight...Northwestern Portion, Nw Winds 15 To 25 Kt Becoming 10 To 20 Kt After Midnight. Elsewhere, Nw Winds 10 To 15 Kt Becoming 5 To 10 Kt After Midnight. Wind Waves 2 Ft Late In The Evening, Becoming 2 Ft Or Less. Nw Swell 3 To 4 Ft At 8 Seconds. Patchy Fog After Midnight.|
|Tue...Northwestern Portion, Nw Winds 10 To 20 Kt. Elsewhere, Ne Winds 5 To 10 Kt With Gusts To 10 Kt Becoming Sw In The Afternoon. Wind Waves 2 To 3 Ft. Nw Swell 3 To 4 Ft At 8 Seconds. Patchy Fog In The Morning.|
|Tue Night...Northwestern Portion, Nw Winds 20 To 25 Kt. Elsewhere, Nw Winds 10 To 15 Kt. Combined Seas 5 To 6 Ft Dominant Period 10 Seconds.|
|Wed...Northwestern Portion, Nw Winds 20 To 30 Kt. Elsewhere, Nw Winds 10 To 20 Kt. Wind Waves 2 To 4 Ft. Nw Swell 4 To 5 Ft At 10 Seconds.|
|Wed Night...Nw Winds 15 To 25 Kt With Gusts To 30 Kt. Combined Seas 6 To 8 Ft Dominant Period 10 Seconds.|
|Thu...Nw Winds 15 To 25 Kt With Gusts To 30 Kt. Combined Seas 7 To 9 Ft Dominant Period 10 Seconds.|
|Thu Night...Nw Winds 20 To 30 Kt. Combined Seas 10 To 12 Ft Dominant Period 14 Seconds.|
|Fri...Nw Winds 15 To 25 Kt With Gusts To 30 Kt. Combined Seas 11 To 13 Ft.|
|Sat...Nw Winds 15 To 20 Kt With Gusts To 25 Kt. Combined Seas 8 To 11 Ft.|
| Area Forecast Discussion|
...UPDATED National Weather Service Los Angeles/Oxnard CA
1121pm PDT Monday September 21 2020
Little change in temperature is expected through Tuesday with night and morning low clouds and fog across the coasts and lower valleys. A slight warming trend will occur Wednesday and Thursday followed by additional warm and dry conditions this weekend.
.SHORT TERM (MON-THU)...21/845 PM.
Weak upper level trough of low pressure across northern and Central California tonight will transition to a more zonal flow pattern on Tuesday, with slight height rises across the region. Onshore pressure gradients were slightly stronger this afternoon and evening as compared to 24 hours ago, peaking at +4.7 mb from LAX to Daggett. This onshore push bringing low clouds and fog into many coastal areas this evening, likely extending into the coastal valleys overnight into Tuesday morning. The marine layer depth will range between 1000 and 1500 feet tonight with little change expected into Tuesday morning, despite a weak eddy circulation spinning up across the coastal waters.
Warm and dry conditions with some gusty south to southeast winds across the San Gabriel mountains sparked additional growth of the Bobcat Fire today, including some impressive plume development near Mount Wilson. South to southeast wind flow will continue to prevail through Tuesday afternoon. High resolution WRF model showing southerly winds of 10 to 15 mph with gusts to 25 mph sustaining overnight across some of the ridges across the northern portions of the San Gabriels from Mill Creek eastward towards Big Pines and extending into some of the adjacent Antelope Valley foothill areas. These breezy conditions combined with continued low humidities will likely sustain fire activity overnight. Little change in the warm and dry conditions expected on Tuesday across the interior, resulting in another day of elevated fire weather concerns across the Bobcat Fire.
The south to southeast upper level wind flow also brought significant smoke impacts into the Antelope Valley today, including the Palmdale and Lancaster metro areas. Smoke will likely be transported into these same areas through Tuesday, then a wind shift to the west on Wednesday will likely begin to improve air quality over the Antelope Valley.
*** From previous discussion *** Onshore pressure gradients will be slightly weaker the next few days as high pressure slowly builds into the region, so not quite as gusty across the mountains and deserts in the afternoons. Very minimal changes are expected with temperatures and humidities however, just a couple of degrees lower Tuesday then higher on Wednesday. This will continue to create some elevated fire weather concerns each afternoon when humidities drop into the lower teens. Wind direction begins to veer to the west and northwest late Wednesday which could be the first evening Sundowners returning to western hills of the south Santa Barbara County coast. Building heigheights will help to lower the marine inversion through Wednesday, so less inland push of low clouds but more likely to see locally dense fog for coastal areas.
On Thursday, there is a weak trough that slides across northern CA that strengthens the northwesterly wind flow heading into Friday. NW to N offshore pressure gradients of 2-3 mb develop over south Santa Barbara County Thursday evening for a potential wind advisory Sundowner by then. Not much change in temperatures yet through the short term.
Long Term - Friday through Monday
A storm system will pass through the Pacific Northwest on Friday and into the northern Rockies by Saturday. This helps high pressure build off the West Coast during the period with northerly flow increasing over southern CA. Warming should take place for the majority of the area with the marine layer becoming more restricted to the LA Basin by Saturday morning. Sundowner winds and I-5 corridor winds will likely add downslope warming to many areas with heigheights building to 592dm or higher by Saturday.
Looking beyond Saturday, the GEFS and ECMWF (European Centre for Medium-Range Weather Forecasts) ensembles both hint at a significant warm up late this weekend and early next week as high pressure encompasses the Great Basin and West Coast. Heights build to 594dm or higher by Monday, which is outside of model climatology (less frequent than 1-day every 10-years) for this time of the year. The bottom-line is that we could be flirting with record temperatures once again with highs 95-105 degrees in the coastal and interior valleys, especially if we get any significant offshore wind regime (ECM deterministic shows -3mb LAX-DAG and -9mb LAX-TPH). The hot and dry scenario will likely become a headline not only for the potential heat stress and record highs, but for fire weather concerns for new and existing fires. Large plume growth would likely contribute to rapid fire growth and fire behavior.
A Small Craft Advisory (SCA) will continue through tonight for the northwestern portion of the northern zone 670 as wind gusts will reach 25 knots through tonight. Elsewhere, winds are expected to remain below SCA (Small Craft Advisory) criteria. By Tuesday evening, there is a 60% chance of SCA (Small Craft Advisory) level winds in zone 670 again with a 40 percent chance in other sections of the outer waters. Gusty NW winds will spread southward by Wednesday and there is a 70% chance of widespread SCA (Small Craft Advisory) level winds across the outer waters through San Nicolas Island Wednesday into Thursday. Good confidence that SCA (Small Craft Advisory) level winds will continue through Friday. There is a 30-40% chance that SCA (Small Craft Advisory) level winds may bleed into the western portion of the Santa Barbara Channel Wednesday through Friday.
.LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3am PDT Tuesday for zone 670. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK (THU-MON).
Strong high pressure is expected to build over the West Coast Sunday and Monday. Heat stress and elevated fire weather conditions will be possible, especially on Monday.