Point Pinos to Point Piedras Blancas out 10 NM Marine Forecast
|Today...Nw Winds 20 To 30 Kt. Gusts Up To 40 Kt This Afternoon. Wind Waves 1 To 2 Ft. Nw Swell 3 To 5 Ft At 10 Seconds And S Around 2 Ft At 14 Seconds.|
|Tonight...Nw Winds 20 To 30 Kt With Gusts Up To 40 Kt. Wind Waves 1 To 2 Ft. Nw Swell 4 To 6 Ft At 12 Seconds And S Around 2 Ft At 15 Seconds.|
|Mon...Nw Winds 15 To 20 Kt With Gusts Up To 25 Kt. Wind Waves 1 Ft. Nw Swell 7 To 9 Ft At 12 Seconds And S Around 2 Ft At 15 Seconds.|
|Mon Night...Nw Winds 10 To 15 Kt. Wind Waves 1 Ft. Nw Swell 6 To 8 Ft At 13 Seconds And S Around 2 Ft At 15 Seconds.|
|Tue...S Winds 10 To 15 Kt. Wind Waves 1 Ft. Nw Swell 5 To 7 Ft At 12 Seconds.|
|Tue Night...S Winds 5 To 10 Kt. Wind Waves 5 To 6 Ft. Nw Swell 4 To 6 Ft At 11 Seconds.|
|Wed...Nw Winds 10 To 15 Kt. Wind Waves 2 To 3 Ft. Mixed Swell Nw 2 To 4 Ft And Sw Around 2 Ft.|
|Thu...Nw Winds 5 To 10 Kt. Wind Waves 1 To 2 Ft. W Swell 3 To 5 Ft And S Around 2 Ft.|
| 301 AM PDT Sun Sep 19 2021 |
Synopsis for the Central California Coast and Bays Including the Monterey Bay, Greater Farallones and Cordell Bank National Marine Sanctuaries - PZZ500
A weak frontal system is passing through the waters this morning. Light southerly winds will quickly shift back out of the northwest later this morning. Light showers over the waters will move out by mid day Sunday. Northwest winds will strengthen in the post frontal environment tomorrow afternoon, with hazardous seas conditions developing over much of the waters, particularly for smaller vessels. Mixed seas persist with a short period northwest swell and a weak longer period southerly swell. An additional longer period northwest swell will arrive around mid week.
| Area Forecast Discussion|
National Weather Service San Francisco Bay Area
451am PDT Sunday September 19 2021
Light rain showers end overnight with a return to drier but still cool conditions Sunday. A rapid shift towards gusty offshore flow and warmer, drier conditions begins Sunday night through early next week. A fire weather watch is in effect for the potential for increased fire risk due to the drying conditions and gusty offshore winds from Sunday night through Tuesday morning.
As of 09:40pm PDT Saturday...KMUX radar shows scattered showers continuing to move eastward over Sonoma and northern Marin Counties. A look at 12-hour precipitation totals shows fairly impressive amounts (~0.5 in) at northern coastal Sonoma sites where SSW winds provided orographic enhancement. Just over the border in Mendocino Co, 1+ inch totals have been measured. Farther south and in the Sonoma Valley, amounts are under a tenth of an inch, and generally a few hundredths or less. No bucket tips in downtown SF as of yet. Hi-res models show the potential for very light scattered showers making their way south through the SF Bay Area and into the Monterey Bay Area overnight. These areas might see a trace to a few hundredths.
Satellite night imagery reveals disjointed marine stratus over the coastal waters, with some stratus developing over coastal land areas. Also, a band of higher level clouds associated with the precipitation and frontal boundary is traversing North Bay. After the frontal boundary passes through, winds will shift to the northwest and clouds will scatter out, though marine stratus will likely linger through the morning. Temperatures will also moderate a bit Sunday as the upper trough over the coast moves inland, and a ridge builds over the eastern Pacific. Still, most areas will remain several degrees below daily normals. A stark transition to drier and warmer conditions with the development of offshore flow occurs overnight Sunday into Monday. Fire Weather Watch goes into effect for the North Bay Mountains and East Bay Hills Sunday at 11 p.m. Read discussion below for more details and for the weekly outlook.
As of 02:30pm PDT Saturday...The first fall-like system of the post-summer dry season has begun to impact the Pacific Northwest and northwestern California through midday today.
Remote sensing imagery shows a narrow, intense band of 200% of normal precipitable water values akin to an atmospheric river along a dynamic cold frontal boundary on the leading edge of this feature. Relatively high rainfall values in excess of 2 inches have been reported farther north near Eureka, CA as this weakening atmospheric river shifts southward towards the Bay Area with lower amounts elsewhere. The Scripps' Center for Western Weather and Water Extremes atmospheric river index rates this storm system as a AR 1 (of 5) for northwestern California (& AR 2-3 in the PacNW), but falls below atmospheric river criteria for our area as it descends south of Cape Mendocino towards the Bay Area through tonight.
This difference is due to the lack of upper level dynamics that are present farther north near the core of the storm, but are lost as the southern flank of the frontal boundary falls away from the parent feature. Instead, orographic lift will be the primary lifting mechanism to generate rainfall from this narrowing precipitable water plume, thus there has been a recent model trend to pull back rainfall amounts across the interior and rain shadowed areas in favor of increasing upslope amounts along the coastal ranges. For example, a few days ago, the forecast called for peak amounts of perhaps 1/3" along the North Bay coastal ranges, but increased that to 1/2" a day or two ago, and today, up to 2/3" is now in range for our wettest spots like Venado. This orographic upshift in the rainfall comes at the cost of a downshift elsewhere, with 0.10-0.15" for the North Bay valleys, 0.04-0.08" for the I80 Corridor and coastal Peninsula, and a few hundredths to a trace along the the remainder of the San Francisco Bayshore and coastal Central Coast. The southern and eastern peripheries of the interior are more likely to see no rain at all than even 0.01".
In terms of timing, the bulk of the rainfall is forecast to arrive between this evening and the overnight period, with the frontal band fragmenting up and the last showers dissipating by sunrise tomorrow morning. Breezy west to northwest winds will develop in the wake of the front later tomorrow afternoon.
The weather pattern will remain progressive and fall-like in the wake of this trough, with a rapid shift towards warmer, drier conditions into early next week in response to a high amplitude eastern pacific ridge building ashore in the wake of the weekend's storm system. This rapid shift will begin to unfold through the day on Sunday and be heralded in with the arrival gusty offshore flow down the western side of Sacramento Valley before funneling through the North and East Bay interior ranges beginning late tomorrow evening. Fuels are near or at record dry levels across these interior slopes, and if today/tonight's storm fails to bring sufficiently wetting rains, then critical fire weather conditions could present themselves as the humidity plummets through Sunday night into Monday morning.
Offshore winds are forecast to peak between 3 am and 9 am Monday morning, with sustained winds 15 to 25 mph with gusts to 30 to 40 mph, locally to 50 mph at ridge top levels. Some mix down to the lower elevations is expected Monday morning, with gusts to 15-20mph possible at places like the Napa valley. A warmer, drier air mass settles in through the day on Monday and, with offshore flow, daytime humidities plummet into the low to mid teens in the drier spots. Poor overnight humidity recoveries are expected for Monday night into Tuesday morning, though on the plus side, winds should be roughly only half as strong as the previous night. So, both Sunday night and Monday night's offshore wind events are borderline critical criteria for varying reasons. For now, no changes are planned for the fire weather watch until we review observational rainfall numbers tomorrow morning. From here, we will decide to cancel or upgrade some or all parts of the watch. For more information, please review the fire weather section written by one of our fire weather incident meteorologists below.
As of 3:34am PDT Saturday...Fire Weather Watch in effect for North and East Bay hills from 11 pm Sunday night through 11 am Tuesday. As noted above in the short term we do expect some wetting rains for coastal Sonoma county. Wetting rains for Napa and East Bay hills look unlikely at this time though a few hundredths is certainly possible. Did look at the updated fuels charts that literally just updated. For the North Bay the ERC readings are down from record highs but still running near the 97th percentile (though thats obviously not accounting for any precipitation we receive the next 24 hours). The Bay Area marine zones that are continuously impacted by the marine layer and thus higher humidity are actually now running below normal for this time of year. Finally the Diablo/Santa Cruz mountains are around the 90th percentile but will likely drop slightly over the next 24 hours.
Anyway, we'll be monitoring rainfall totals closely through Sunday morning. High confidence for warming and drying to start Sunday afternoon but the airmass being replaced is very moist as noted by the high PW values. Watch start time of 11 pm Sunday still looks good with latest NAM model showing an abrupt increase in northeast wind around 925 mb between 06-09z. Given the stability profile would expect most of the winds to stay at or above 2000 feet with gusts generally in the 30-40 mph range (50 mph Mt Saint Helena). RH values look to stay above 30% into Monday morning which may be a limiting factor. In addition should wetting rains occur across much of the North Bay that could put us out of Red Flag criteria for 24 hours after the rain ends.
High confidence for rapid warming and drying Monday as temps will quickly rebound into the upper 80s and 90s with humidity dropping into the teens as persistent but light offshore winds continue. The entire Bay Area will dry out Monday night into Tuesday but wind speeds look light as the strongest pressure gradient stays over the northern Sierra.
General trend looks to be above average temps and continued dry next week though the models are grappling with a potential cut- off low. The more likely scenario is a transient midweek system passes to our north with another potential offshore wind event late in the week followed by building high pressure and unseasonably warm and dry weather through the end of the month.
as of 04:42am PDT Sunday...A weak frontal system is passing through the waters this morning. Light southerly winds will quickly shift back out of the northwest later this morning. Light showers over the waters will move out by mid day Sunday. Northwest winds will strengthen in the post frontal environment tomorrow afternoon, with hazardous seas conditions developing over much of the waters, particularly for smaller vessels. Mixed seas persist with a short period northwest swell and a weak longer period southerly swell. An additional longer period northwest swell will arrive around mid week.
NOAA San Francisco Bay Area Office: Watches - Warnings - Advisories
Small Craft Advisory...Monterey Bay
from 2 PM Small Craft Advisory...Pigeon Point to Point Pinos 0-10 nm
from 2 PM Small Craft Advisory...Point Pinos to Point Piedras Blancas 0-10 nm
from 2 PM Small Craft Advisory...Point Arena to Point Reyes 0-10nm
from 2 PM