Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco CA

932 pm PDT Mon may 18 2026

Short Term

, Issued at 1251 PM PDT Mon May 18 2026 (This evening through Tuesday)

Gusty offshore winds have started to come down across the region and will continue to ease through the remainder of the day. Current gusts across the lower elevations are peaking around 25-30 mph with gusts across the higher elevations peaking between 35-45 mph. The strongest gust observed during this wind event was 86 mph right around midnight at Mt. Umunhum where the station is at an elevation of 3319 feet. This tracks pretty well with when the SFO-WMC pressure gradient peaked (-7.60 mb) around 1AM and again around 5AM. The SFO- WMC gradient is currently around -4.3 mb and is expected to continue easing through the remainder of the day. Winds remain lightly offshore across the interior through the remainder of today into tomorrow but winds will be weaker. We will see a return to our normal breezy afternoon/evening winds that ease overnight starting Tuesday.

Upper level ridging continues to dominate the Pacific Ocean while broad upper level troughing prevails over the Western United States. At the surface, high pressure prevails over the Pacific while a coastal trough develops along the California coast. Warmer temperatures are expected to continue Tuesday through Thursday. This is thanks both to ridging offshore suppressing the marine layer and a warmer, drier airmass moving in in the wake of this weekend's strong offshore winds. Interior high temperatures will generally be in the 80s with the hottest portions of the North and East Bays in the low 90s. Coastal areas will be slightly cooler in the 60s to mid 70s. Dry conditions are expected to prevail through much of the upcoming week with daytime relative humidity values dropping into the 10's to 20's. While fire weather concerns are lower now that the winds are easing, fine fuels (grass, shrubs) are dried out and are ready to burn. If you are engaging in any outdoor activities involving flames or are towing something, keep a close eye on it and prevent sparks from spreading.

Long Term

..issued at 1251 PM PDT Mon May 18 2026 (Tuesday night through next Sunday)

The overall pattern remains the same for much of the upcoming week. High temperatures will stay above seasonal normals through Thursday with highs in the 80s to low 90s across the interior and 60s to 70s along the coast. Patchy moderate heatrisk is forecast across urban areas but it is note widespread enough to necessitate a Heat Advisory. If you are spending time outdoors this week make sure to drink plenty of water and take breaks in the shade as needed. Winds generally remain offshore with diurnally breezy conditions expected. Friday into the weekend a pattern change looks likely. Long range guidance suggests upper level ridging will weaken and shift westward over the Pacific while broad upper level troughing dominates the West Coast. With high pressure shifting away, onshore winds return and the marine layer will be able to redevelop by late week. A shallow (~500 ft) marine layer will redevelop mid to late week but will deepen to ~1000 ft by Friday. This, and receding high pressure, will kick off a cooling trend with interior temperatures returning to the 70s to low 80s and coastal areas to the 60s. The return of the marine layer will help to alleviate dry daytime conditions,

Aviation

(18z TAFS) Issued at 1021 AM PDT Mon May 18 2026

Currently VFR at all terminals. High confidence in VFR and diurnal winds prevailing through the TAF period. Winds may become calm and/or light and variable overnight.

Vicinity of SFO, Currently VFR with westerly flow. High confidence in VFR and diurnal winds prevailing through the TAF period. Westerly winds will continue to diminish with the potential to become calm and/or light and variable overnight.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, Currently VFR and calm at MRY and VFR with northerly flow at SNS. High confidence in VFR and diurnal winds prevailing through the TAF period.

(06Z TAFS) Issued at 932 PM PDT Mon May 18 2026

Vicinity of SFO,

SFO Bridge Approach,

Monterey Bay Terminals,

Marine

(tonight through next Sunday) Issued at 932 PM PDT Mon May 18 2026

Conditions will continue to improve tonight as northerly breezes continue to diminish. Rough seas will prevail in the outer waters with moderate seas in the inner waters. Hazardous conditions for small craft will persist through the week across the northern outer waters due to rough seas and strong northerly breezes.

Watches, Warnings, Advisories

Ca, Coastal Flood Advisory until 3 AM PDT Tuesday for CAZ506.

PZ, Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

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

Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt Pinos 10-60 NM.

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