Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco CA

1258 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

VFR conditions prevail through the TAF period. Breezy and gusty northeast winds will gradually diminish through the next couple of hours as an onshore push returns to the coastal regions this afternoon, with the coastal breeze continuing through the evening. Breezy winds will continue across the interior mountains of the Bay Area through the night, with northeast winds spreading across the interior valleys Tuesday morning towards the end of the 24-hour TAF period. Beyond that, Tuesday's coastal breezes look to be stronger than today's.

Vicinity of SFO, VFR conditions through the TAF period. Breezy and gusty northeast winds will turn more northwesterly through the afternoon, before diminishing through the evening and remaining light overnight through Tuesday morning. West-northwest winds will resume on Tuesday afternoon.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, VFR conditions through the TAF period. Breezy northwest winds will develop imminently and continue into the evening. Winds remain light overnight before resuming Tuesday afternoon after the end of the TAF period.

Marine

(today through Saturday) Issued at 1021 AM PDT Mon May 18 2026

Winds continue to diminish throughout the marine environment, but moderate to rough seas and moderate to fresh northwest breezes will still offer hazardous conditions for small craft into the mid weak before easing for most zones. Fresh to strong northwest breezes will remain hazardous for small craft into the late week for the northern outer zone.

Watches, Warnings, Advisories

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

PZ, Small Craft Advisory until 3 PM PDT this afternoon for SF Bay N of Bay Bridge.

Small Craft Advisory until 9 PM PDT this evening for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm.

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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