textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1130 PM PDT Mon Sep 7 2026

- Warming and drying trend will bring widespread moderate to major HeatRisk through Thursday

SHORT TERM

Issued at 1151 PM PDT Mon Sep 7 2026 (Tonight through Wednesday)

24 hour trends are warmer and drier. Already a warming trend is underway with increasing thermal and height ridging aloft. Any marine layer influence is confined to within a few hundred feet of sea level with only a few patches of fog along the Big Sur coast at the moment.

The large scale pattern shift to warmer/hotter temperatures involves both the retrogression (westward motion) of the subtropical ridge over the central U.S. and the eventual merging of tropical energy and moisture from steadily decaying TS Marie and a cut-off low far to our west (also forecast to retrogress). Strengthening 500 mb heights, large scale compression and the Sep sun angle will raise temperatures up further Tuesday, peaking well above normal both Wednesday and Thursday. A little bit of a wildcard to this week's pattern is the northward intrusion of tropical moisture including some warm air advection (far from decaying TS Marie) which will be west of the 500 mb ridge axis. Higher to much higher precipitable water will arrive here, model forecasts are still showing near 1.40" in the Bay Area mid-week, near the max moving average for Oakland upper air early-mid Sep climatology. Mid and high clouds will increase, but we don't really know quite yet with high confidence how well the models may or may not be handling mid-level convective potential (mucape) with disagreement among various output from e.g. from the HRRR and GFS. Good to see the GFS shows very minimal to no mucape anyhow. Also, with hotter surface temperatures (greater internal energy) air parcels will stay capped as long as the atmosphere is stable.

Hot temperatures for this week are not quite in reach of long term record highs at this point, except Half Moon Bay may get close if there's no shallow sea breeze mid-week as an offset to the temperature. Will continue to monitor.

A Heat Advisory is in effect for the entire forecast area from 10 AM Wednesday to 10 PM Thursday. We've had a nice 10 to 11 day run of below normal temperatures (due to a large scale trough), especially inland, so the sudden reversal in temperatures will be noticeable if not already. With widespread moderate to major HeatRisk, this affects most individuals sensitive to heat, especially those without effective cooling and/or adequate hydration. Please stay out of direct sunlight, and stay properly hydrated. Hot conditions can cause heat illnesses.

Also, minor coastal flooding is likely within a small window of time of about 1 hour nearest high tide Tuesday (possibly Wednesday as well) for bayshore locations of Marin County. Impacts will include minor flooding of the lowest lying areas directly along the shoreline. At the San Francisco tidal gauge, high tide is expected to be 1 ft above normal at 9:59 PM 9/8. At this time we are messaging it here and will include messaging in social media vs issuing a coastal flood advisory for Tuesday.

The Beach Hazards Statement was allowed to expire.

LONG TERM

Issued at 1151 PM PDT Mon Sep 7 2026 (Wednesday night through next Monday)

Well above normal hot weather continues Thursday. Thereafter northwest winds and a gradual weakening of the 500 mb ridge will bring a cooling trend for late in the week and weekend. Daytime highs will cool back to near normal Friday, then possibly a few degrees below normal for the upcoming weekend. Late week weather will be dry with the mid-latitude pattern settling back in.

AVIATION

(12Z TAFS) Issued at 410 AM PDT Tue Sep 8 2026

With light offshore flow the marine layer is struggling to form, and VFR conditions are expected through the day. There is a slight chance of low ceilings at the coastal terminals this morning, but any stratus that manages to form will be battling dry air and should clear by the early afternoon. Winds will be lighter than normal, with a moderate onshore breeze in the afternoon. High clouds will be nearly overcast at times this afternoon and evening.

Vicinity of SFO...High confidence in VMC through the TAF period. GFLAMP shows less than 10% chance of ceilings below 3,000' this morning. The wind direction is a little more uncertain for the first portion of the TAF. Light WNW winds are currently being reported, but the typical morning NE breeze is likely to become established for a few hours before the sea breeze takes over in the afternoon. High cloud coverage will increase through the day.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The VFR forecast is a little more vulnerable here, with a 20% chance of low ceilings before 18Z. A cyclonic eddy has been moving north along the Central Coast overnight, with a bank of coastal stratus forming in the onshore wind along its southern flank. As this feature continues north, it could impact Monterey, but the SW direction and shallow surface inversion makes it tricky to actually reach the terminal. For wildfire aviation purposes, the localized marine layer south of the eddy is 500 ft deep. With SW flow, the stratus that has formed along the Big Sur Coast may not clear until well into the afternoon. On the other hand, there is very high confidence in VFR conditions today at the inland aviation bases.

MARINE

(Today through Sunday) Issued at 410 AM PDT Tue Sep 8 2026

Tuesday will feature a gentle NW breeze with a moderate-rough SW swell. The swell will subside over the next couple of days, while the NW winds increase to a moderate breeze.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Heat Advisory from 10 AM Wednesday to 10 PM PDT Thursday for CAZ006-502>506-508>510-512>518-528>530.

PZ...None.