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

(12Z TAFS) Issued at 424 AM PDT Fri Sep 4 2026

A weak cold front is exiting the southern Bay Area and moving through the Central Coast this morning. Showers remain in the vicinity of SJC and LVK this morning but are expected to progress eastward over the next few hours. Patchy stratus has developed this morning after high clouds associated with the cold front cleared out. Stratus is more widespread across the North Bay where confidence is higher in MVFR to LIFR conditions prevailing. Comparatively, stratus is patchier over the Bay Area which is decreasing confidence as to how long stratus will linger this morning. Included a tempo for patchy stratus at most sites this morning where confidence was lower through 16Z. Breezy onshore winds return during the afternoon before winds ease overnight. Stratus is likely to return tonight but it will be later than normal. The forecast currently leans on later arrivals between 09-12Z with the marine layer remaining mixed out through Saturday. Initial guidance suggests the marine layer will try to redevelop around 2000 ft by late this weekend so we may see more traditional stratus patterns return by then.

Vicinity of SFO...Stratus has cleared in the vicinity of SFO and the SF Bay with confidence low that stratus will successfully redevelop this morning. VFR conditions prevail this afternoon/evening with scattered clouds around 5000 feet moving in. Guidance is mixed as to if stratus will reach SFO tonight. For now, leaned on the side of VFR conditions continuing given the marine layer being mixed out/struggling to redevelop. If stratus does develop it will likely be later in the night (approx. after 08Z).

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The cold front is making its way through the Central Coast with MVFR CIGs prevailing at both sites. As the front moves southwards, ceilings are expected to lower slightly and be more on the IFR-MVFR border. Stratus will clear by late morning with VFR persisting into the evening before stratus returns late tonight. Breezy onshore winds return during the afternoon and evening before winds decrease overnight.

MARINE

(Today through Wednesday) Issued at 424 AM PDT Fri Sep 4 2026

A gentle to moderate west to northwesterly breeze will continue through the weekend with diurnal fresh to strong gusts across the Monterey Bay, the Big Sur Coast, and near Point Reyes. Occasional fresh to strong gusts are possible within the San Pablo and San Francisco Bays. More widespread fresh to strong gusts return early next week with hazardous conditions for small craft likely before winds diminish mid to late week. Long period southerly swell associated with tropical activity well to our south will arrive today and linger into next week. Unsettled weather is possible mid to late week as tropical moisture tracks northwards in the Eastern Pacific.

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 through Monday evening for CAZ006-505- 509-529-530.

Coastal Flood Advisory from 4 PM this afternoon to 9 PM PDT this evening for CAZ506.

PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay.