Marine Weather and Tide Forecast for Union City, CA

SHORT TERM
Issued at 1203 AM PDT Fri Apr 10 2026 (Today and tonight)

A surface low near 37 N, -128 W in the Eastern Pacific Ocean will continue to trek eastward through the night. Rain showers from the main rain band will push into the area around 2-3 AM and push off to the northeast by the afternoon. Isolated rain showers/thunderstorms will remain possible behind it. Rainfall totals will be dependent upon where rain showers/thunderstorms develop and thunderstorm development will be dependent upon where breaks in the clouds allow for the convective temperature to be realized. Rainfall is expected to be strictly beneficial. The only caveat would be for minor flooding in poor drainage and urban areas if a heavier rain shower/thunderstorm develops and/or rain showers/thunderstorms train. Thunderstorms will pose the risks of lightning, locally heavy rainfall, erratic/gusty winds, and small hail. Weak low- level shear does not support a mention of rotation leading to tornadoes and/or waterspouts.

LONG TERM
Issued at 1203 AM PDT Fri Apr 10 2026 (Saturday through Thursday)

An upper-level low in the Gulf of Alaska will dig down the West Coast and absorb the first low as it does so on Saturday. This will be a whole new ballgame as this system is much more dynamic by nature with the inclusion of the jet stream. The cold front will sweep through Saturday afternoon and evening bringing widespread rainfall to the region. Even with the QPF continuing to trend higher with 1"-2" and up to 4" in the coastal ranges when all is said and done, this rainfall is expected to be purely beneficial thanks (I guess) to the dry March that we are coming off of. The three ingredients for thunderstorms of lift, instability, and moisture will all be in place Saturday. The merging of the two lows and the associated cold front will offer lift, the atmosphere will destabilize as cold air filters in aloft, and remnant tropical moisture will remain in place through the cold frontal passage.
Thunderstorms will pose the risks of lightning, locally heavy rainfall, erratic/gusty winds, and small hail. With the reintroduction of the jet stream and veering winds in the low- levels, rotation yielding waterspouts and/or weak tornadoes is possible. The slower trend of returning to ridging is thanks to the low filling instead of remaining progressive Sunday. As a result, wraparound rain showers and thunderstorms are now in the forecast all of Sunday. Cold air with remnant moisture will allow for snow across the highest peaks on Sunday. Anglers should take special note of the expected weather and have a plan to reach safe harbor quickly when the weather turns. Even without thunderstorms, the marine conditions will deteriorate through the day Saturday. If thunderstorms develop, the associated wind gusts are capable of capsizing small vessels. Fishing leads to more lightning deaths in the U.S. than any other activity. When thunder roars, head indoors!

Heights will slowly begin to rise on Monday, kicking off a warming and drying trend. Widespread below normal temperatures are expected Monday before slowly rebounding to seasonal normals by Thursday. As we get back into the growing season, patchy frost is possible in sheltered locations Monday morning due to the combination of cold conditions and remnant moisture. The frost risk decreases through the week as temperatures slowly rise and drier air filters in.

AVIATION
(12Z TAFS)
Issued at 442 AM PDT Fri Apr 10 2026

A band of moderate to heavy showers is moving slowly eastward over the forecast area. In addition to showers during the 12z TAFs, there's a slight chance to chance of thunderstorms today.
Conditions are otherwise forecast VFR-MVFR.

Vicinity of SFO...VFR-MVFR. Showers with a convective potential today, but will monitor radar and satellite before adding VCTS to the TAF. Southeast wind 5 to 10 knots becoming south-southwest 10 to 15 knots in the afternoon

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR-MVFR. Showers. Southeast to southwest winds 5 to 12 knots.

MARINE
(Today through Wednesday)
Issued at 435 AM PDT Fri Apr 10 2026

A low pressure system with showers and a chance of thunderstorms will move eastward over the coastal waters and bays today. This low will merge with an energetic low from Alaska Saturday and Sunday. The result will be rain, heavy at times, including a chance of thunderstorms Saturday through Sunday. High pressure builds behind the system with fresh northwest winds developing early next week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory from 9 AM to 9 PM PDT Saturday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.

Small Craft Advisory from 9 AM to 3 PM PDT Saturday for Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory from 3 PM to 9 PM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM.