Marine Weather and Tide Forecast for Union City, CA

SHORT TERM
Issued at 1223 AM PDT Sat Apr 18 2026 (Today and tonight)

A progressive upper level ridge axis will shift east across our area this morning, while temperatures inland climb into the upper 70s to low 80s. Locations most likely to reach or exceed 80 will be in the interior valleys of the South Bay and Central Coast where there will be plenty of sunshine and light winds. Coastal locations will be only slightly warmer than Friday with weak onshore flow during the day out ahead of the developing offshore disturbance. Even with the ridge exiting to the east, overnight lows into Sunday will be more mild than we've seen the last few nights with increasing mid/high level cloud cover insulating some of todays heat.

LONG TERM
Issued at 1223 AM PDT Sat Apr 18 2026 (Sunday through Friday)

Sunday will be a nice transition day as the pattern changes for the first half of next week. Overall, consensus is improving but the timing of the first ejecting wave of the developing upper low is still in question. What we do know is that deep onshore flow will at least bring a return of stratus along our entire Pacific Coast Sunday night. Our official forecast has slight chance PoPs over the North Bay late Sunday evening but any rainfall initially would be measured in the hundredths. By sunrise Monday morning we may see more impactful rain over the North Bay coastal ranges then shift into the interior valleys. The slow moving system with notable longitudinal orientation out ahead initially will see areas of showers training over the North Bay. The WPC does have much of Sonoma County in a Day 4 Excessive Rain Outlook on Monday. The second wave approaches the coast overnight Monday into Tuesday as the associated trough becomes negatively tilted providing added lift and increasing baroclinic instability by late morning/early afternoon for any showers/storms moving onshore. The system will be slow to move onshore initially, but once inland it will eject east quickly. Attm, the pattern indicates another disturbance splitting off the back side with an inside slider trajectory for the second half of next week.

AVIATION
(06Z TAFS)
Issued at 953 PM PDT Fri Apr 17 2026

Breezy onshore winds are diminishing across much of the region with only relatively breezy conditions continuing at SFO. Winds remain on track to continue diminishing overnight and become variable. LAMP guidance continues to indicate stratus is possible at HAF but confidence remains low. If stratus were to develop at HAF it would likely be short lived between 12Z-18Z. Elsewhere, VFR conditions prevail through the remainder of the TAF period. Stratus looks to return shortly after 06Z Sunday.

Vicinity of SFO...VFR. Breezy onshore winds continue to diminish tonight before becoming variable through tomorrow morning. Winds restrengthen during the afternoon/evening with winds around 15 knots expected. Some potential for stratus to return towards the end of the TAF period but confidence is currently lower.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Light, variable winds continue overnight with breezy onshore winds redeveloping during the afternoon/evening. Winds peak between 10 to 13 knots.

MARINE
(Tonight through next Thursday)
Issued at 953 PM PDT Fri Apr 17 2026

Fresh north to northwest winds will continue to diminish through Saturday with moderate winds expected Saturday afternoon into Sunday. Winds shift southerly Sunday ahead of an incoming low pressure system and cold front. Winds are expected to strengthen ahead of cold frontal passage Monday into Tuesday with localized strong gusts expected. Moderate seas, rain, and a slight chance of thunderstorms Monday and Tuesday.

MARINE
(Tonight through next Thursday)
Issued at 953 PM PDT Fri Apr 17 2026

Fresh north to northwest winds will continue to diminish through Saturday with moderate winds expected Saturday afternoon into Sunday. Winds shift southerly Sunday ahead of an incoming low pressure system and cold front. Winds are expected to strengthen ahead of cold frontal passage Monday into Tuesday with localized strong gusts expected. Moderate seas, rain, and a slight chance of thunderstorms Monday and Tuesday.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...None.