Marine Weather and Tide Forecast for Castro Valley, CA

SHORT TERM
Issued at 235 PM PDT Sun Apr 19 2026 (This evening through Monday)

Pleasant end to the weekend for the Bay Area and Central Coast weather wise with filtered sunshine and seasonably mild temperatures. Max temps today will peak in the 60s to mid 70s with a few interior spots making a run at 80 plus.

Stepping back and taking look at the bigger picture reveals a system lurking off the coast. In fact, pretty impressive looking visible satellite imagery this afternoon. A discernible circulation is spinning off the PacNW with a band of clouds wrapping around the system and stretching along the West Coast.
The circulation is an anomalously deep upper low. At the surface is a double barrel low pressure system with a marked frontal structure. The surface low and front will begin to inch its way eastward Sunday evening and Sunday night. The advancing cold front will bring increasing clouds and a few scout showers to the northern coastal waters and far northern Sonoma county. Not expecting much in the way of accumulating precip with these leading showers through Sunday night.

More widespread precip is expected on Monday as the highly amplified upper jet begins to phase off the CA coast. Light to moderate rain will begin across the North Bay toward the end of the AM commute. Rain will spread S and E through the day with the passage of the cold front. Expect the evening commute to be pretty messy with wet roads.

In addition to the rain on Monday, southerly flow will ramp thanks to a tightening surface gradient. Winds are initially strongest over the waters before hitting the coast and inland areas by the afternoon. Not strong enough for a wind advisory, but general gusts in the 30-40 mph range seems reasonable. Given the southerly flow, initial rain chances for some areas will be eaten thanks to downslope flow and rain shadowing.

As for temperatures, despite a pattern change temperatures will be mild since the region will be in a warmer sector until fropa.
Given the solid S flow think there could be some enhanced downslope warming - thinking Monterey.

LONG TERM
Issued at 238 PM PDT Sun Apr 19 2026 (Monday night through next Saturday)

Monday looks wet, but Tuesday may end up being a little more dynamic thanks to convection. A few things we'll be watching for Tuesday: cold pool aloft behind the front destabilizing the atmosphere, approaching upper low, position of left exit of jet aloft, and wind profiles relating to low level shear. While those pieces varying from model to model, enough of a signal is present to justify having thunderstorms in the forecast for Tuesday.
Putting things into better context, the ECMWF Extreme Forecast Index has strong signal for CAPE over the coastal waters giving more confidence to thunderstorms. SPC Day 3 outlook does have the entire region in a general mention of thunderstorms.

Monday's rain and Tuesday additional shower activity should be mostly beneficial rain, but given the convective nature local ponding/minor flooding is possible. Lingering showers will continue into Wednesday afternoon thanks to a trailing shortwave behind the departing upper level low/trough.

Warmer and drier conditions there after.

AVIATION
(00Z TAFS)
Issued at 425 PM PDT Sun Apr 19 2026

A slow moving cold front approaching the coast will dominate the weather through this TAF period and beyond. High cloud coverage will increase overnight as winds trend southerly. Rain should reach the North Bay late Monday morning and move south through the day. This rain will be preceded by high MVFR or VFR clouds for all terminals.

Vicinity of SFO...There is very little chance for low ceilings before 12Z when the more direct impacts from the approaching cold front start to move over the terminal. Rain should reach the terminal sometime between 18Z and 00Z before the intensity increases Monday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The front is creeping very slowly and impacts will take longer to reach the southern terminals. The best chance for rain onset is Monday afternoon/evening.

MARINE
(Tonight through next Friday)
Issued at 425 PM PDT Sun Apr 19 2026

Calm conditions continue into the night. Breezy and gusty winds build ahead of a slow moving cold front that arrives on Monday.
Rain will accompany the cold front starting Monday and lingering into early Wednesday. Chances of thunderstorms will move through the waters for much of Tuesday. Dry weather returns late in the week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory from 9 AM to 9 PM PDT Monday for SF Bay N of Bay Bridge.

Small Craft Advisory from 9 AM Monday to 3 AM PDT Tuesday for Mry Bay.

Small Craft Advisory from 3 AM to 9 PM PDT Monday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory from 3 AM Monday to 3 AM PDT Tuesday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.