textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 143 AM PDT Sun Oct 18 2026

- Hazardous beach conditions continue through tonight

- Cooling trend begins today and persists into the work week

- Light rain showers possible mid-week

SHORT TERM

Issued at 145 PM PDT Sun Oct 18 2026 (This evening through Monday night)

24 hour trends are cooler across much of the forecast area, due to cool air advection from the surface up through the lower levels of the atmosphere. Daytime highs today will peak close to October 18th normal highs. A pattern shift to long wave troughing is developing and the trough will usher in below to much below mid-late October normal temperatures during the upcoming week. Wet weather will accompany the trough by mid-week.

LONG TERM

Issued at 145 PM PDT Sun Oct 18 2026 (Tuesday through next Saturday)

The northern hemisphere long wave trough pattern contracted somewhat after late September 2026 (interestingly e.g. after the persistent far downstream Nor'Easter). Just what storms do, the north-south meridional temperature/energy exchanges temporarily reduced the meridional temperature gradient resulting in some contraction that increased the chances we'd have long wave ridging (and warm/hot spells) which we had at times in October. Warm/hot spells are most frequent here in Sep-Oct after a long dry summer, still relatively high sun angle and especially when coupled to (dry, downsloping) offshore winds.

As mentioned a pattern shift to long wave troughing is taking place, not so much because of an expansion in long wave troughs rather the result of a now progressive zonal pattern entering the entire western CONUS. Strong polar jet stream winds on the back side of the trough will drive the trough south-southeastward from the Gulf of Alaska temporarily cutting off a 500 mb low ~ a few hundred miles to our west-southwest from late Monday night to Wednesday night. During this time the subtropical jet stream will merge with the polar jet stream near the base of the newly forming 500 mb cut-off low. The cold core low will dig deep passing over higher sea surface temperatures in contrast to the cold core low, steepening temperature lapse rates and instability and water vapor availability will cause showers and thunderstorms to form. The greatest instability will be over the coastal and offshore waters while the low approaches land during mid-week it'll encounter marginal diurnal surface instability and much less if any land surface based instability at night. Precipitable water is forecast to reach near the 90th percentile during the mid week timeframe; cold air within the low will help result in measurable rain and any thunderstorm development will be "wet" rain producers (vs "dry" thunderstorms). As of current time, the southern half of the forecast area stands the best chance of highest measurable rain with lesser amounts to the north.

Forecast rainfall amounts for Tuesday night through Thursday: 0.10" to 0.25" in the North Bay, 0.20" to 0.50" across the rest of the Bay Area and 0.33" to 1" across Monterey and San Benito counties. Southerly breezes will prevail, but the low will be wrapping cold air around from the south as well and daytime highs are forecast to remain below normal during the period. Far inland highs will struggle to reach 70F in rain cooled air Wednesday and Thursday.

For late in the week dry weather will return along with an increase in daytime highs reaching back to the 70s inland Friday and Saturday with 60s closest to the coastline.

AVIATION

(18Z TAFS) Issued at 1020 AM PDT Sun Oct 18 2026

Currently IFR-VFR. The marine layer was observed around 500 feet this morning and is expected to deepen through the TAF period. Stratus is off the coast with a feed through the Golden Gate Gap. With the deepening of the marine layer, moderate confidence in MVFR conditions returning to all terminals tonight as it's able to penetrate farther inland. Onshore winds will prevail.

Vicinity of SFO...Currently VFR with northwesterly flow. Moderate confidence in an MVFR ceiling developing at the terminal tonight, likely early. The San Bruno Gap has been able to hold off stratus so far, but if the marine layer deepens to around 1,000 feet, there will be nothing stopping IFR/MVFR stratus from reaching the terminal earlier. Westerly/Northwesterly winds will prevail, becoming gusty in the afternoon and evening.

SFO Bridge Approach...The San Mateo Bridge Approach will likely have clouds at or below FL070 from 04Z to 17Z.

Monterey Bay Terminals...Currently VFR and calm at both terminals. Moderate confidence on MVFR conditions returning to the terminals tonight. Diurnal winds will prevail.

MARINE

(Today through Friday) Issued at 1020 AM PDT Sun Oct 18 2026

Moderate to fresh northwesterly breezes will prevail through Monday, bringing widespread hazardous conditions across the coastal waters Sunday afternoon. Winds will diminish and back to become southerly Tuesday and Wednesday before returning to moderate to fresh northerly breezes Thursday. Rough seas across the outer waters will subside to become moderate Monday, rebuilding to become rough Tuesday. Light rain showers are expected Tuesday through Thursday.

BEACHES

Issued at 1020 AM PDT Sun Oct 18 2026

Hazardous beach conditions will be present at Pacific Coast beaches Sunday. Long period 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 jetties, piers, rocks, and other waterside infrastructure as waves can sweep across the shoreline without warning, pulling people into the sea. Remain out of the water to avoid hazardous surf with strong rip currents and never turn your back on the ocean!

Sarment

MTR WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement until 9 PM PDT this evening for CAZ006- 505-509-529-530.

PZ...Small Craft Advisory until 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.