Marine Weather and Tide Forecast for Union City, CA

UPDATE
Issued at 926 AM PDT Thu May 22 2025

Fairly clear skies across the region this morning with only a few patchy areas of stratus along the coastline. The Fort Ord Profiler shows the marine layer is around 1,000 ft and is expected to deepen to around 1500 ft tonight. Elevated fire weather concerns continue in areas where grasses are cured due to dry daytime conditions and gusty winds between 25-35 mph. Otherwise, no updates needed.

SHORT TERM
(Today and tonight)
Issued at 238 AM PDT Thu May 22 2025

The marine layer is being observed at 800 feet by the Fort Ord profiler with satellite just starting to show some stratus forming over Tomales Bay and along the San Francisco Peninsula Coast.
Despite this, the 00Z KOAK sounding revealed a LowRH (surface-850 mb) value of 25%, a MidRH (850mb-650mb) value of 9%, and a precipitable water value of 0.45 inches which is slightly above the 10th percentile of 0.42 inches for 00Z May 22nd. An upper-level shortwave trough will skirt the region today, bringing temperatures back down to seasonal normals. Of more impact will be the strong onshore winds that it brings with gusts of 25-35 mph expected over the waters, along the immediate coastline, through northwest/southeast oriented valleys, and in the higher terrain.
These winds in conjunction with poor relative humidity (both overnight recovery and daytime minimum) will continue to support elevated fire weather conditions.

LONG TERM
(Friday through Wednesday)
Issued at 238 AM PDT Thu May 22 2025

An approaching second, deeper upper-level shortwave trough will deepen the marine layer and finally ease fire weather concerns for the time being as excellent relative humidity recovery (70%+)
returns to all but the highest terrain of the Central Coast.
Sensibly, temperatures will drop to 5 degrees below normal, dubbing tomorrow the coolest day of the week. Heights will begin to build and temperatures rebound to seasonal normals Saturday as a positively tilted upper-level longwave ridge builds into the West.
Due to the orientation of the upper-level pattern, the warmest day for the Bay Area will be Saturday with the Central Coast having to wait until Sunday to achieve that feat. The unofficial start of Summer (Memorial Day) will feel anything but with below normal temperatures brought to you by a dry cold front. The previously mentioned upper-level longwave ridge will build and broaden across the Western two-thirds of CONUS with an upper-level shortwave trough likely to undercut it, resulting in split flow and unimpactful weather for our region Tuesday and Wednesday.

AVIATION
(18Z TAFS)
Issued at 1125 AM PDT Thu May 22 2025

Primarily VFR through the TAF period with patchy periods of MVFR-IFR stratus in the San Francisco Bay and Monterey Bay region. Winds strengthen during the day with gusts between 20 to 32 knots across portions of the Bay Area and Central Coast. Winds ease overnight before locally breezy conditions develop during the day again tomorrow. Confidence is low that fog will develop across the North Bay Valleys tonight with conditions looking to be too dry for fog development.

Vicinity of SFO...VFR becoming IFR overnight. Patchy IFR stratus will develop overnight around 10Z before dissipating by mid Friday morning. Strong winds gusting up to 32 knots are expected this afternoon before easing overnight to around 12 knots. Gusty winds up to 27 knots will return during the day on Friday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR becoming MVFR overnight. MVFR CIGs look to return tomorrow morning around 13Z and persist through late tomorrow morning. CIGs are borderline MVFR/IFR with some potential for IFR CIGs to develop overnight. Breezy onshore winds continue through the TAF period with lighter, more variable winds expected overnight.

MARINE
(Today through Tuesday)
Issued at 926 AM PDT Thu May 22 2025

Widespread hazardous marine conditions continue today as strong northwesterly breezes with near gale to gale force gusts and rough seas persist. Fresh to strong northwesterly breezes and moderate to rough seas will prevail Friday through Monday.

FIRE WEATHER
Issued at 238 AM PDT Thu May 22 2025

The combination of poor daytime relative humidity of 15-25% and onshore winds with gusts of 25-35 mph along the immediate coastline, in northwest/southeast oriented valleys, and in the higher terrain will continue to support elevated fire weather conditions today. The greatest period of concern is today in cured grass areas. Remain fire wise and do not be the reason for fire starts.

Sarment

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for SF Bay N of Bay Bridge.

Small Craft Advisory from 3 PM to 9 PM PDT Friday for SF Bay N of Bay Bridge.

Gale Warning until 9 PM PDT this evening for Mry Bay.

Small Craft Advisory until 9 AM PDT Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Gale Warning from 9 AM Friday to 3 AM PDT Saturday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 3 PM PDT Friday for Pt Reyes to Pigeon Pt 0-10 nm.

Gale Warning from 3 PM Friday to 3 AM PDT Saturday for Pt Reyes to Pigeon Pt 0-10 nm.

Gale Warning until 3 AM PDT Friday for Pigeon Pt to Pt Pinos 0- 10 nm.

Gale Warning until 9 PM PDT Friday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM.