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PZZ455 Cape Mendocino To Pt Arena Out 10 Nm- 842 Pm Pdt Fri Sep 22 2023
Tonight..N winds 5 kt. Waves nw 4 ft at 10 seconds. Patchy fog.
Sat..SE winds less than 5 kt...becoming nw 5 to 10 kt. Waves nw 3 ft at 9 seconds.
Sat night..NE winds 5 to 10 kt. Waves nw 3 ft at 11 seconds.
Sun..SE winds 10 to 20 kt. Waves nw 4 ft at 9 seconds.
Sun night..SE winds 20 to 30 kt. Waves S 7 ft at 7 seconds...and W 3 ft at 11 seconds.
Mon..S winds 15 to 25 kt. Waves W 11 ft at 13 seconds.
Tue..W winds 5 to 10 kt. Waves W 14 ft at 15 seconds.
Wed..NW winds 5 to 15 kt. Waves nw 7 ft at 12 seconds.

PZZ400 842 Pm Pdt Fri Sep 22 2023
Synopsis for northern california waters..Winds and seas continue to weaken tonight and into Saturday. Southerlies will develop Sunday ahead of a front. Strong gale force wind gusts are expected Sunday afternoon into Monday morning, with the strongest gusts expected north of cape mendocino.

FXUS66 KEKA 222159 AFDEKA

AREA FORECAST DISCUSSION National Weather Service Eureka CA 259 PM PDT Fri Sep 22 2023

SYNOPSIS
Quiet, seasonable weather will continue through Saturday. Gusty south wind and rain remains on track to arrive throughout the area late Sunday through Monday.



DISCUSSION
Relatively zonal flow aloft has helped bring a period of quiet, seasonable weather. Most of the interior has reached the upper 70s today with Coastal highs near 60. Winds are mostly calm, though low pressure building over the North Pacific has generally helped turn wind southerly. This has helped push most wildfire smoke out of the area and into Oregon. Isolated marine stratus has formed offshore which may push back right along the coast late tonight.
Similar quiet weather will continue through Saturday with only a very slight cooler trend. By late Saturday afternoon, high clouds will likely to begin streaming into the area.

A deep trough and associated surface low pressure remains on track to dip over the Pacific Northwest late Sunday into early next week.
Models show a clear atmospheric river being pulled from the topical Pacific into the Northern California Coast. The GFS shows integrated water vapor transport around 800 kg/ms. This puts the event on par with storms that are much more common later in the season. Between Sunday evening and through Monday. Much of Humboldt and Del Norte Counties will most likely receive between 1 to 3 inches of rain.
Uncertainty remains high for the southern half of the area as it lies along the edge of the moisture band, but generally less than 1 inch is expected for Mendocino and Lake Counties. See the hydro discussion below for more rain details.

In addition to rain, the strongest pressure gradient along the edge of the trough will drive gusty south winds late Sunday through Monday morning. Currently the NBM is placing the best chance at the high elevations of Humboldt and Del Norte Counties. The NBM show an 80% chance or more of gusts in excess of 30 mph at mid elevation slopes and higher and along the coastal plain. Chances of gusts over 40 mph vary from 50 to 80% above 3000 ft. The only place with a real risk of these gusts outside of high elevation ridges are int he exposed coastal around Crescent City. The only areas with any real risk of gusts over 50 mph are restrained to the high ridges of the King Range. The risk of downed trees and power lines is elevated because this is the first major southerly wind of the season and because most trees still hold their leaves. While no wind product was issued this afternoon, the need for one remains likely and will be watched closely has high resolution guidance becomes available over the next 24 hours.

As the system begins to move east. There is a threat of isolated thunderstorms Monday afternoon. At that point, the GFS shows up to 500 J/Kg of most unstable CAPE. Any showers would likely be restrained offshore and to the immediate coast north of Trinidad Head. Showers will gradually ease off through Tuesday. In the longer range, about 20% of cluster ensemble members show wetting rain late in the week, but most show a dry but generally quiet and seasonable pattern. /JHW

AVIATION
Thick layers of wildfire smoke covered most of Del Norte and Humboldt. The result was MVFR to low VFR reported Cigs/Vis at ACV and CEC today. A southerly surge of marine stratus by late morning moved along the North Coast...simultaneously resulting in IFR Cigs into early afternoon. An eddy off the Point ST. George coast allowed stratus to keep rotating over CEC after midday. Overnight, various model guidances are suggesting IFR conditions returning to the Coast by mid Saturday morning. Winds will remain S-WSW at the coast today; perhaps with a few breezes. Stratus inundated the Mendocino Coast near FT Bragg and spilled into local valleys...but the layer was shallow enough not to overspill into inland mountain valleys.
However, southerly flow up the Russian River resulted in IFR conditions spreading into UKI this morning. Not convinced at this time that UKI will see another morning of broken low clouds, but did add some scattered clouds in the morning. /TA



MARINE
Winds and seas have continued to slightly diminish this afternoon. Winds are south to southwest closer to the coast while the remain northerly well off the coast and these will persist tonight. Saturday the winds will start to switch to the south in the north as an unseasonable stronger storm starts to build into the area. These will gradually spread south into the southern waters Saturday night. The winds are expected to increase rapidly across the area Sunday afternoon as the cold front approaches. Confidence is growing that we will see gales in the northern outer waters so have added a gale watch to highlight that for Sunday night and Monday morning. These will likely move closer to the coast, but confidence is lower so have held off on issuing anything at this point.

Immediately behind the front Monday night and Tuesday a strong swell moves in. This is currently expected to build to around 14 to 16 feet at 15 seconds by Tuesday afternoon. Confidence is not particularly high at this point, however both the ECMWF and GFS wave models are showing similar solutions. MKK



HYDROLOGY
The highest rainfall totals are expected to favor the N portion of the area. The latest QPF totals from late Saturday through Monday night range from around 3.5 inches over the windward sides of Del Norte mountains to around 0.2 inches over S Lake County. Rainfall amounts across the windward faces of the King Range of SW Humboldt County are expected to be over 2 inches due to orographic enhancement. Downslope flow along the North Coast will likely push rainfall later and keep it around 1 inch. Higher amounts are certainly possible due to the moderate to occasionally strong water vapor transport, particularly across Del Norte County. Looking a bit deeper at confidence, the NBM places a 70 to 100% chance of more than 1 inch of rain throughout Humboldt and Del Norte Counties.
This chance changes to 40 to 70% for more than 2.0 inches of rain.
There is less than a 30% chance of more than 1.0 inch of rain anywhere south of the Humboldt County line.

Will continue to highlight locally heavy rainfall in Del Norte and Humboldt counties on Monday, with the potential for rock slides in the mountainous terrain, especially near recent burns on highways 199 and 96. For the most part, rainfall rates are expected to be below thresholds for burn scar debris flows, but higher rainfall rates are possible as precipitation transitions to more convective, aided by orographic effects. As the first large rain of the season and with recent burn scar, a flood watch has been issued for Del Norte and interior Humboldt Counties.

Rivers are forecast to rise in response to the expected rains, but river levels will remain well below monitor stage, even with the higher outlier ensemble forecast basin amounts. Most rivers are likely to rise only 1 to 2 feet. /SEC+JHW



EKA WATCHES/WARNINGS/ADVISORIES
CA...
Flood Watch from Sunday afternoon through Monday evening for CAZ101-102-104>106.

NORTHWEST CALIFORNIA COASTAL WATERS...
Gale Watch from Sunday afternoon through Monday morning for PZZ470.

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Shelter Cove
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Sat -- 07:04 AM PDT     Sunrise
Sat -- 07:55 AM PDT     4.43 feet High Tide
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