Marine Weather and Tide Forecast for San Lorenzo, CA

SHORT TERM
Issued at 1053 PM PDT Fri Oct 16 2026 (Tonight through Sunday)

Clear skies continue this evening, but the offshore winds have calmed substantially. The SFO-WMC gradient peaked at -13.7 mb Friday morning and has since weakened to -7.8 mb. 24 hours ago Mt.
St. Helena was reporting NNE winds of 44 mph. Now it's NW at 5.
The 500 mb ridge over northern California is weakening. The 00Z balloon measured the 500 mb height at 5910m, down from 5930m at 12Z. That's still above the 90th percentile for this time of year, but the trend will accelerate through the day Saturday as the Channel Islands cut-off low gets absorbed back into the jet stream, bringing more zonal flow to the upper levels.

At the surface this means the return of onshore winds and the start of a cooling trend. Max temperatures Saturday are expected to be a couple degrees cooler than Friday. It will still be a warm, sunny day for everyone. The bigger change is Sunday. A new deep low pressure system approaches from the west. This system will bring back the marine layer and drop the max temperatures by another 10-15 degrees. It will also bring another round of wind, but from the west this time. Our current forecast shows gusts up to 50 mph through Altamont Pass Sunday night. That's the outlier.
Most places will have gusts in the 15-25 mph range.

LONG TERM
Issued at 1053 PM PDT Fri Oct 16 2026 (Sunday night through next Friday)

A brief period of zonal flow aloft gets interrupted on Monday as an upper-level trough pushes southward along the California coast.
Ahead of the low pressure system, onshore winds increase across the Bay Area and Central Coast with a deepening marine layer, resulting in cooling to near seasonal temperatures. The trough becomes a cut- off low by Tuesday and lingers off the Central Californian coast before gradually propagating inland through Southern California Wednesday evening into Thursday. The system's position allows for the reinforcement of cold air advection across the Bay Area and Monterey Bay regions through the end of next week.

In terms of precipitation chances, light rain showers are possible Tuesday through Thursday across the Bay Area and Monterey Bay regions. The coastline and southernmost extent of the Central Coast have a 40-60% probability of light rain meanwhile the North, East, and South Bay have a 20-40% chance. In addition to rain, there is potential for thunderstorm development during the aforementioned time period. The three main ingredients required for thunderstorm development are instability, lift, and moisture. Given the complex terrain within the region, we can guarantee some degree of orographic lifting as the system moves inland. Both the European and GFS ensemble members are hinting at precipitable water values around the 75th percentile for this time of year, so we can also check moisture off our thunderstorm ingredient list. Finally, we have instability. European ensemble members are exhibiting 500 mb temperatures around -15 to -20 degrees Celsius, which falls below the 10th percentile for this time of year. Meanwhile, the 850 mb temperatures are around the seasonal normal of 9 to 12 degrees Celsius. Atmospheric instability may arise from the mixing of air masses, particularly when a cold air mass sits on top of a warm air mass. Since cold air is more dense than warm air, it will sink to the surface while forcing the ascent of warm air. As warm air rises, it cools adiabatically and condenses, resulting in latent heat release, which further warms the surrounding air allowing for increased vertical mixing. This process is dependent on other thermodynamic factors, however the structure of our cut-off low supports an unstable system due to vertical mixing.

Despite all of the above, there is still high uncertainty regarding the rainfall and thunderstorm potential as it is dependent on the exact trajectory of the cut-off low and the alignment of various elements. Be sure to check back on the forecast for updated information.

AVIATION
(12Z TAFS)
Issued at 457 AM PDT Sat Oct 17 2026

No major changes to the TAF package this morning. Light offshore flow is expected this morning, with onshore flow returning this afternoon. We'll still have to work through some drier air so VFR conditions are expected to prevail. The marine layer is expected to establish to around 500-1000ft by 12Z so we could see some stratus develop along the coast.

Vicinity of SFO...Winds are expected to become offshore for a few hours this morning, with onshore flow returning by the afternoon.
Some guidance shows the potential for a reduced visibility, which would coincide with the marine layer getting to around 500-1000ft.
Opted to keep KSFO and KOAK VFR for the time being.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Light offshore winds will continue this morning, with onshore winds returning later this afternoon. The marine layer starts to re-establish and bring reduced visibility to the region. This appears to have the best chance around sunrise, opted to start hinting at the potential since it is just outside the TAF cycle.

MARINE
(Today through Thursday)
Issued at 255 AM PDT Sat Oct 17 2026

Gentle to moderate northerly breezes this morning, with winds gradually increasing as a cold front sweeps through this weekend.
Northerly winds will become strong across the northern outer waters this evening and then hold through Sunday. Moderate to fresh northwesterly breezes Monday will diminish and back toOffshore winds are expected for through the morning with onshore winds by late morning or early afternoon.
Onshore flow should continue through the early evening, before another round of offshore winds returns late evening and into early Saturday morning. VFR conditions will prevail. become westerly Tuesday. Moderate seas will prevail through today, but will gradually be building and become rough across the outer waters tonight through Tuesday. Light rain is expected Monday into Tuesday.

FIRE WEATHER
Issued at 1053 PM PDT Fri Oct 16 2026

While the offshore winds have calmed substantially, hot and dry conditions will continue through Saturday. Max temperatures will be in the mid 80s to low 90s with RH dropping into the the teens for nearly all areas away from the immediate coast. A significant cool-down arrives Sunday through Monday with light rain possible mid-week.

BEACHES
Issued at 919 PM PDT Sat Oct 16 2026

Temps cool on Saturday, but still pleasant weather. People may head to beaches to recreate, but should use caution. Hazardous beach conditions will develop at Pacific Coast beaches this weekend and likely into next week. Long period (17 seconds)
southerly/southwesterly swell will bring an increased risk for sneaker waves and strong rip currents with breaking waves of 7 to 12 feet. Remain off of jetties, piers, rocks, and other waterside infrastructure as waves can sweep across the shoreline without warning, pulling people into the sea. Never turn your back on the ocean!

MM/Sarment

MTR WATCHES/WARNINGS/ADVISORIES
CA...Beach Hazards Statement through Sunday evening for CAZ006-505- 509-529-530.

PZ...Small Craft Advisory from 3 AM to 9 AM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt Reyes 10-60 NM.