textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1151 PM PDT Thu Sep 3 2026

- Coastal Flood Advisory in effect around high tide bayside Marin County Friday afternoon and evening

- Hazardous beach conditions at Pacific Coast beaches Friday through Monday

- Below normal temperatures through the weekend, a gradual warming and drying trend Monday through Wednesday

SHORT TERM

Issued at 103 AM PDT Fri Sep 4 2026 (Today and tonight)

A 500 mb low pressure system (geopotential height 555 decameters, much below normal for early September) will move onshore over Oregon today. Over our forecast area 500 mb heights are in the 570 decameters range which is near the 10th percentile for early September. If it was any time in the cool season 570s would not be a big deal or impressive. However, for early September much below normal heights over our area are due to chilly temps in the air column above per inspection of the 925 mb, 850 mb, 700 mb temps on the Oakland air upper sounding. These readings are near or less than the 10th percentile as well, i.e. at the lower end (cool temps) but within Oakland upper air long term climatology for early September since 1948. The current weather pattern is a great example of water vapor rich air (precipitable water was 1.35", near the early Sep max moving average) and cool air within a trough of low pressure resulting in areas of measurable precipitation, in early September (normally the third driest month behind July and August) when it's typically warmer/hot and dry when e.g. Sep-Oct favor offshore winds. The larger scale northern hemispheric pattern continues to be active with ~ 6 long wave troughs, a signature of rather strong jet stream winds, wind shear and unsteady flow. The August Pacific Decadal Oscillation remained negative. The North Pacific high and its clockwise wind flow remained rather robust. A strong equator to pole temperature gradient continues, and not to mention three hurricanes at the same time in the eastern Pacific, a powerful show of thermodynamics (flow of heat) from sea surface to the highest thunderstorm cloud tops. Just like a cup of hot coffee, an open system where heat and mass are free to flow, 100% whenever there is an imbalance heat and mass will flow.

Back to our area, within the aforementioned long wave trough a much smaller scale cool frontal boundary with areas of light measurable rain will continue to move southeastward over the forecast area today. Early September rainfall has reached a few records, we plan to send a record event report on this overnight. Dry weather revisits the area today in the post frontal cooler than normal air mass for early September. Forecast daytime highs will vary from the 60s coastside/bayside to the 70s/80 inland.

LONG TERM

Issued at 103 AM PDT Fri Sep 4 2026 (Saturday through next Thursday)

Jet stream winds and additional shortwave energy will generally reach the base of the 500 mb low pressure system over the west. This will provide forward motion to the low, nudging the southern U.S. high forward through early to mid next week. The redevelopment of 500 mb troughing over the eastern Pacific during the middle of next week will provide a small chance of entraining tropical moisture. This is a long time from now, it's a low confidence forecast, but bears monitoring.

AVIATION

(06Z TAFS) Issued at 1014 PM PDT Thu Sep 3 2026

The front is working its way through the Bay Area and into the Central Coast, with light rain being reported at the terminals around San Francisco. North Bay counties have dried out, leaving behind it clearing skies and mainly VFR conditions. The question for tonight will be, do we continue to clear or will be get some pockets of sunrise stratus and fog after the front passes? The latest guidance leans towards the latter with stratus and fog developing around sunrise and eroding a few hours after that. VFR conditions then look to prevail through the forecast period. Medium confidence in the forecast.

Vicinity of SFO...The front is here while writing the AFD and light rain is being observed around the San Francisco Bay terminals along with MVFR cigs. Expect these conditions to linger through the next few hours, with rain chances diminishing as the front moves south. The question for these KSFO and KOAK will be, does the stratus last. Guidance seems to be the most bullish here with cigs flirting around SF Bay. Opted keep the pessimistic forecast in, though it might be more of a TEMPO situation or just outside of the range rings. Conditions for sure look to improve around and after sunrise, with VFR conditions prevailing during the day. Onshore winds pick up mid to late afternoon, with sustained speeds around 12-15kt and gusts up to 22-25kt through sunset.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Low clouds are lingering around Monterey Bay, with high clouds passing overhead as the front arrives. Lower clouds should make it to KMRY and KSNS later tonight, with perhaps even some VCSH or -SHRA for a few hours seeing how well the cold front has held up. MVFR to potentially IFR cigs will be possible as the front passes through, with conditions gradually improving behind it.

MARINE

(Tonight through next Wednesday) Issued at 1014 PM PDT Thu Sep 3 2026

Rain chances will continue to diminish tonight, with gentle to moderate northwesterly breezes expected in wake of the frontal passage. Diurnal fresh to strong gusts return within the Monterey Bay, the Big Sur Coast, and near Point Reyes Friday into the weekend. Widespread fresh to strong gusts return by early next week across the coastal waters, decreasing to moderate to fresh breezes by midweek. Long period southerly swell associated with tropical activity well to our south will reach the coastal waters Friday and continue into early next week.

BEACHES

Issued at 1010 PM PDT Wed Sep 2 2026

A Beach Hazards Statement is in effect Friday-Monday as the swell from both Hurricane Marie and Hurricane Karina reaches the coast. As these hurricane whip up the ocean, the waves travel over 1,000 miles in all directions, gradually flattening out to low amplitude, but long period swell. These waves aren't very intimidating if you're on a boat in the open ocean, but the long period allows them to push much farther up the beach. Long period swell always increases the chance for sneaker waves, but that's particularly true this weekend since there are 2 different sets of southerly swell, and their energy will periodically combine. In addition to sneaker waves, expect strong rip currents and breaking waves up to 10 ft. As this is a holiday weekend and the weather is otherwise pretty nice, the exposure to the risk is high. Avoid the water if you're not an expert swimmer. If caught in a rip current, swim parallel to shore until you stop feeling the pull. Even on the beach, be prepared for sneaker waves this weekend and never turn your back on the ocean.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement from 6 AM PDT Friday through Monday evening for CAZ006-505-509-529-530.

PZ...None.