textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1247 PM PST Wed Dec 31 2025

- High astronomical tides combined with storm surge will bring minor to moderate coastal flooding around high tide through Sunday.

- A prolonged rainy period starts today.

- Strong southerly winds are likely Friday and into Saturday morning.

SHORT TERM

Issued at 1247 PM PST Wed Dec 31 2025 (This evening through Thursday)

Light to occasionally moderate rain continues to spread northward and will increase in coverage and intensity through this evening. This is a result of PWAT values between 1.00-1.30" advecting in from the south as a mid/upper level cut off low remains just west of the Central Coast. As the low pressure shifts into the Central Coast on Thursday morning, there will be a slight chance of thunderstorms late morning into the afternoon over this region. By late Thursday afternoon and into the evening, rain will be more focused along the coastal terrain as a warm front moves northward across the region. Rain shadowed valleys may not see any rainfall from Thursday afternoon through about Friday night.

LONG TERM

Issued at 1247 PM PST Wed Dec 31 2025 (Thursday night through next Tuesday)

A more typical atmospheric river is set to move through the region late Friday and into early Saturday morning. This is when more widespread rain and stronger winds are forecast. Wind gusts are currently forecast to be 45-55 mph along the coast, in the higher terrain, and northwest to southeast oriented valleys. Elsewhere expecting 35-45 mph gusts from late Friday night through Saturday morning. Wind Advisories are likely during this time frame, yet the forecast models have trended about 6 hours later from yesterday. So, still refining the forecast as we move closer to the event. From 4 PM Friday through 4 PM Sunday, rainfall totals will range from 2.00- 4.00" in the coastal ranges, 1.50-3.00" in the North Bay, 1.00-2.00" in San Francisco and other coastal areas, and generally less than 1.25" in the rain shadowed valleys. There is generally less than a 20% chance of thunderstorms as the main frontal band moves through and in wake of the passage through Sunday afternoon. Given the recent rainfall from last week, this will lead to nuisance flooding for poor drainage areas, urban areas, and rises on flashy creeks/streams. This will be especially so if a heavier rain shower and/or thunderstorm where to move over any give area. However, widespread river flooding is not anticipated at this time.

From the previous forecaster: "A new low pressure system and associated cold front is possible Monday or Tuesday. The ensemble clusters have differing opinions on the strength and timing of this feature, but they all show a trough off the coast, which is enough to keep rain chances around through the entire 7-day forecast period. KMUX will stay in precip mode for the foreseeable future."

AVIATION

(18Z TAFS) Issued at 1002 AM PST Wed Dec 31 2025

Light rain has returned to much of the Bay Area and the Central Coast. Current ceilings are VFR but guidance shows them dropping to MVFR by late this afternoon/early this evening. Confidence on timing of ceilings dropping is low to moderate with moderate confidence and models in agreement that CIGs will drop to around 2000-2500 ft for much of this TAF period. Models do show CIGs dropping to IFR overnight but confidence is currently low for that scenario. Winds stay out of the south to southeast and remain breezy through the forecast period. Gusts to around 20 to 25 knots are expected at breezier sites (SFO, OAK, and SNS with some potential for gusts at HAF and MRY) Thursday morning. Maintained visibilities dropping slightly as rain moves in. However, I followed a similar trend as the previous forecaster and kept drops in visibility limited to around 4SM to 5SM given light rainfall expected. Models show visibilities dropping down to 2-3SM but confidence is low that will occur unless locally moderate to heavy rain is able to develop.

Vicinity of SFO...Light showers are located offshore of SFO with scattered showers to move in throughout the remainder of the morning. Moderate confidence in MVFR CIGs developing by late this afternoon/early this evening with low confidence that CIGs will become IFR overnight. Winds generally remain southerly and are expected to strengthen by tomorrow morning. Currently kept gusts to around 18 knots at SFO tomorrow but this may need to be adjusted upwards to between 20-25 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Light rain is moving over the Monterey Peninsula with VFR conditions to continue. Ceilings lower to MVFR by late this afternoon/early this evening as showers become more scattered in nature. Winds remain southerly through the TAF period with winds strengthening after 06Z. Gusts will strengthen at SNS overnight with highest confidence in gusts to 26 knots developing but there may be occasional gusts up to 30 knots tomorrow morning.

MARINE

(Today through Monday) Issued at 859 AM PST Wed Dec 31 2025

Moderate to fresh winds and moderate seas continue into Thursday. Widespread light rain and a low potential for thunderstorms across the southern waters continues into Thursday. Winds rapidly strengthen from strong to gale force by early Friday as a second, stronger, system arrives. Periods of moderate to heavy rain and a slight potential for thunderstorms are expected Friday into Saturday. Winds diminish early Sunday but breezy conditions and rain showers continue into next week.

BEACHES

Issued at 859 AM PST Wed Dec 31 2025

Perigean spring tides (King Tides) will impact the region through Sunday. This is due to the combination of the full moon on 1/3, lunar perigee on 1/1, and perihelion on 1/3. In other words all three planetary bodies are lined up and close to each other. In addition to the high astronomical tide, the incoming low pressure system will bring strong southerly winds, generating some storm surge. The combination of these factors will bring minor to moderate coastal flooding to the low-lying areas near shorelines and tidal waterways during high tide through Sunday. At the San Francisco tidal gauge, high tide is expected to be 2.0 ft above normal at 8:41 AM Thursday, 2.2 ft above normal at 9:34 AM Friday, 2.2 ft above normal at 10:26 AM Saturday, and 1.8 ft above normal at 11:18 AM Sunday. These predictions include up to 1 foot of storm surge that will enhance the astronomical tide and flooding threat. High tide varies up to 90 minutes earlier or later along the Pacific Coast and through the San Francisco Bay, respectively.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory until 2 PM PST Sunday for CAZ006-505-506- 508-509-529-530.

PZ...Small Craft Advisory from 9 PM Thursday to 3 AM PST Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Gale Warning from 3 AM to 9 AM PST Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory from 3 AM to 3 PM PST Thursday for Pigeon Pt to Pt Pinos 0-10 nm.

Gale Warning from 9 PM this evening to 3 PM PST Thursday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory from 9 PM this evening to 3 PM PST Thursday for Pigeon Pt to Pt Pinos 10-60 NM.

Small Craft Advisory from 3 AM to 9 AM PST Friday for Pigeon Pt to Pt Pinos 10-60 NM.