Marine Weather and Tide Forecast for Castro Valley, CA

UPDATE
Issued at 849 AM PST Thu Nov 6 2025

Mixed bag across the forecast area this morning, either sunshine or clouds/patchy fog. Quite the change from yesterday morning where it was wet and windy. Much less wind this morning, and while there are bucket tips over the last hour or two - thinking those are condensation tips and not precip as satellite shows clear skies in some areas. Bay Area radars are pretty quiet and not showing any showers at the moment like earlier this morning. This is also supported by Bodega Bay and Cazadero profilers showing no precip. Lastly, AQPI radar in Santa Rosa is also quiet. Will need a quick update to remove showers this morning up north. That being said, still thinking some showers will return tonight and will leave those in the forecast.

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SHORT TERM
Issued at 226 AM PST Thu Nov 6 2025 (Today and tonight)

Compared to yesterday, conditions are much more tranquil as our potent upper system continues to move into the northern High Plains. However, westerly moist flow within the 700-500mb layer along with modest 925-850mb warm air advection will at a minimum re-inforce cloud cover, particularly for the Bay Area and points northward. Low level ascent is most prominent across the North Bay and as a result, I've opted to make some slight alterations to increase the areal coverage of 20-40% PoPs and latest radar imagery supports this. The thick low/mid level clouds may hinder widespread dense fog development here, and I've opted for "patchy" fog wording here. Farther south, low level flow is a little more southerly which may not encourage as much ascent and this minimizes the chance for rain showers and low clouds (except along the immediate coast). With the relatively clearer conditions in tandem with recent rainfall, the potential for a greater coverage of radiation fog, some dense, will reside across the South Bay and parts of the Central Coast. We'll monitor trends for any potential dense fog products.

With the zonal flow aloft, it's unlikely that our next front will make much southward progress during the day today. Persistent westerly warm/moist flow in tandem with orographic ascent ahead of this feature will continue to support the development of rain showers across the North Bay. Rain amounts are anticipated to average around 0.10", mainly across the northern Sonoma Coastal Ranges. While meaningful PoPs are advertised as far south as Santa Rosa, the probability of exceeding 0.10" here is around 5%.

Later this evening and tonight, a mid-level jet max characterized by 100 knot flow will swing through central Oregon. As surface cyclogenesis ensues, this should help drag the aforementioned frontal boundary southward. Eventually, this feature will undergo frontolysis as the parent surface low lifts eastward.

LONG TERM
Issued at 226 AM PST Thu Nov 6 2025 (Friday through Wednesday)

Before our next front completely loses steam, it still appears that it'll interact with a moist airmass and kick off some showers across the North Bay through pre-dawn hours on Friday. Measurable rainfall does seem plausible even south of the Golden Gate. PoPs range from near 70% along the Sonoma/Mendocino County line to 15% just south of Half Moon Bay Friday morning. Some of the newer NBM probabilities do suggest that low PoPs may be needed as far south as the Santa Cruz mountains, but for now, confidence isn't high that sufficient ascent will reside that far south. Trends in short term NWP will be monitored. Rain amounts still appear relatively lighter compared to the last day or so with values largely under 1/4 of an inch.

Little to no potential for rain is forecast for the entire area starting Friday afternoon and into the weekend. Ridging is anticipated to build in across the eastern Pacific which turns our mid/upper level flow more northwest and northerly. Offshore flow at least within the 500-925mb layer should at scour out low level moisture. This will translate to warmer and more pleasant conditions outdoors with highs ranging between the mid 60s to mid 80s. If headed to the beach, beware that long period westerly swell will increase the risk for rip currents and sneaker waves.
We've highlighted this threat with a Beach Hazard Statement. For more details, see the "beaches" section of the AFD.

Model guidance seems to be coming into slightly better agreement with a fair to foul weather transition next week. About 1/4 of GFS and ECMWF ensemble members advertise that the H5 ridge will start to breakdown and troughing will return to the west coast by Monday evening, with a majority of the multi-model ensemble advertising that this will not occur until about 24-48 hours later. For now, will ride with the blend for PoPs in the extended.
These spatial discrepancies equate to a broad-brush and low confidence rain forecast for Tuesday and Wednesday. Initial glances at some AR tools would point to more beneficial rainfall, but as we venture closer, we'll refine timing, rain amounts, and impacts.

AVIATION
(18Z TAFS)
Issued at 1118 AM PST Thu Nov 6 2025

Overcast conditions continue in the North Bay and at HAF while other sites are clearing. Expect cloud cover to continue to erode into the afternoon leading to VFR for all but HAF which keeps CIGs through the TAF period. Expect moderate winds for the afternoon that reduce into the evening. CIGs return to the Monterey Bay into the evening, but an eddy over the bay itself will lead to moments of clearing.
The rest of the region will see widespread CIGs return into the late night with some pockets of fog. Cloud cover begins to erode in the mid morning, but widespread VFR isn't expected until that afternoon.

Vicinity of SFO...VFR through and moderate winds last into the early night. Winds reduce in the early night as IFR CIGS fill over the terminal and around the SF Bay. Cloud cover will be slower to erode into Friday but skies look to clear in the afternoon with moderate northwest winds arriving.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR and moderate winds last into the evening before winds weaken and low CIGs return. An eddy over the bay looks to pull cigs away from SNS into the night, but push them back over the terminal into early Friday. CIGs look to erode in the mid morning as moderate northwest winds rebuild.

MARINE
(Today through Tuesday)
Issued at 1118 AM PST Thu Nov 6 2025

Rough seas are expected across the waters through the day and into Saturday. Seas slowly begin to abate into Saturday afternoon.
Winds and seas stay light through much of the next work week, before another storm system arrives into the next weekend.

BEACHES
Issued at 1118 AM PST Thu Nov 6 2025

Hazardous beach conditions will persist through Saturday for all coastal beaches. Expect an increased risk of sneaker waves and rip currents as well as breaking waves up to 25 feet. Remain out of the water to avoid hazardous swimming conditions, stay off of jetties, piers, and other waterside infrastructure, and never turn your back on the ocean! The increased risk for sneaker waves and rip currents will linger Friday through early Saturday morning with westerly swell quickly rebuilding.

MTR WATCHES/WARNINGS/ADVISORIES
CA...Coastal Flood Advisory until 2 PM PST Saturday for CAZ006-506- 508-529-530.

Beach Hazards Statement through Saturday morning for CAZ006-505- 509-529-530.

PZ...Small Craft Advisory until 9 PM PST this evening for Mry Bay-Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory until 3 AM PST Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 3 AM PST Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.