Marine Weather and Tide Forecast for Hercules, CA

SHORT TERM
(This evening through Friday)
Issued at 252 PM PDT Thu May 22 2025

Strong onshore winds gusting between 30 to 35 mph along the coast, mountain gaps and passes, and northwest/southeast oriented valleys continue overnight into Friday morning. Elevated fire weather concerns persists through this evening with dry conditions across the interior (relative humidity values in the 15 to 30% range). The primary concern continues to be for areas where grasses are cured (grasses have browned/dried out). An approaching upper level trough will help to bring in more moist air and deepen the marine layer to 1500 ft tonight. This increase in moisture will ease the elevated fire concerns that we have seen over the last few days with overnight relative humidity values increasing to 70-90% across the interior. Patchy stratus cover will return to coastal areas and the San Francisco Bay region overnight but is not expected to be widespread. Breezy winds will continue again on Friday, but, they will be weaker than those observed on Wednesday/Thursday. Winds are expected to gust between 20-25 mph on Friday along the coast, through the valleys, and across the elevated terrain. Temperatures across the North Bay hold steady in the upper 70s on Friday while temperatures across the rest of the Bay Area will drop by about 5 degrees. This will bring most locations across the South Bay and East Bay into the upper 60s to mid 70s and into the 50s to 60s along the San Francisco Peninsula. Residents of the interior Central Coast may feel a more substantial drop, with highs to drop from the upper 80s to low 90s on Thursday to the low to mid 80s on Friday. If you find yourself thinking that this is a bit chilly for May, you would be correct in that Friday's forecast temperatures are expected to be around 10 degrees below normal for this time of year.

LONG TERM
(Friday night through next Wednesday)
Issued at 252 PM PDT Thu May 22 2025

Surface high pressure and a positively tilted upper level trough will build in over the weekend into next week over the West Coast.
This will help to keep our temperatures and winds in a fairly stable pattern this week. For temperatures, highs will stay in the 70s to low 80s across the interior and upper 50s to mid 60s along the coastline. Diurnally breezy winds between 20 to 30 mph will continue across the coastline, valleys, and across the elevated terrain through Wednesday. Overall this upcoming week looks pleasant with temperatures running around 10 degrees below normal. That will change by late next week with temperatures looking to rise again and CPC forecasting above normal temperatures from the end of May into June. In the longer run, both the GFS and ECMWF are starting to generate a cut-off low oriented offshore to the southwest of the California coastline. While this is still a ways out, it may be worth keeping an eye on for the possibility of offshore winds across the CWA

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 3 AM PDT Friday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.

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 Saturday 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.