Castro Valley, CA 94546 Weather

: New UPDATE, MARINE:

Key messages

Updated at 1200 AM PDT Fri Oct 30 2026

- Moderate coastal flooding at high tide for Bayshore and Pacific Coast locations through the weekend

- Seasonal to slightly below seasonal temperatures through the extended forecast

- Potential for rain Saturday and again next week

Update

Issued at 906 AM PDT Fri Oct 30 2026

High based rain showers and/or sprinkles continue to move out of our region this morning, yet chances reamin through the rest of the day as most of the high resolution forecast models depict the potential for them to continue across the Central Coast until sunset. There is a 5-10% probability of thunderstorms across interior Monterey County and San Benito County by mid afternoon, yet conditions do not appear favorable for them to occur. However, cannot rule out a strike or two over the aforementioned areas. That said, any stronger cell that does develop would likely produce wetting (>0.10) rainfall. Thus, we will continue to monitor throughout the day. For more information on the Coastal Flood Advisory, please see both the Short and Long Term discussions below.

RGass

Short term

Issued at 1200 AM PDT Fri Oct 30 2026 (Today and tonight)

Satellite imagery is showing a pretty robust stream of high clouds into the Bay Area and Central Coast, stemming from the remnants of a low from the Central Pacific merging into a wider trough pattern across the West Coast. Earlier tonight, some of the embedded moisture gave us some rather cool cloud tops on satellite and echoes from the KMUX radar and several stations within Monterey and San Benito Counties have reported measurable rainfall (up to a tenth of an inch) over the last few hours. Although shower coverage has since decreased, chances for showers have been added to the forecast for Monterey and San Benito Counties through the rest of the morning.

Otherwise, the weather pattern continues to be dominated by a deep ridge that has set up across the West Coast. Morning lows will hover in the lower to middle 40s in the North Bay valleys, which have remained rather clear overnight, and the upper 40s to the middle 50s across the rest of the Bay Area and Central Coast. Highs today range from the middle to upper 60s in the inland valleys and the SF Bayshore, the lower 70s along the warmest parts of the southern Salinas Valley, and the upper 50s to lower 60s close to the Pacific coast.

A combination of high astronomical tides and surge from thermal expansion and low pressure effects brings the risk of minor coastal flooding along the Bayshore at the San Pablo, San Francisco, and Monterey Bays, and the Pacific coast, at high tide today. At the San Francisco tidal gauge, high tide is expected to be 1.9 ft above normal (7.7 ft MLLW) at 2:39 PM today, including around 1.5 ft of surge residual.

Long term

Issued at 1200 AM PDT Fri Oct 30 2026 (Saturday through Thursday)

The trough will start to progress eastwards on Saturday, as the trough axis digs into California and an upper level ridge behind it starts to push it onshore and into the Great Basin. As it does, it pulls in a couple of jet streaks eastwards. One of them will be a meridional (north to south) jet streak that will set up to the west of the trough, paralleling the coast of Oregon and northern California. Quick meteorology lesson -- within a jet streak, the balance of all the forces in the atmosphere means that there are two regions where cyclogenesis and unsettled weather are favored. Those two regions are on the right side of the entrance to the jet streak (looking along the direction of wind flow) and the left side of the exit of the jet streak. It just so happens that the left exit region of the jet streak off Oregon and northern California will help provide an impulse to a bit of upper level vorticity, which grows into a bigger blob of vorticity, that pushes the trough ever more southwards until it develops into its own low pressure system off of southern California and the northern part of Baja California. That is the storm system that will come into southern California and bring some of the attendant moisture into our region. Meanwhile, weaker low pressure systems might develop across northern California as the jet streak approaches the coast. Rain totals look to be around a tenth to a quarter of an inch within the far interior of Monterey and San Benito Counties, around a few hundredths of an inch in the rest of the Central Coast and orographically favored regions of the coastal Bay Area, to a few sprinkles in the interior Bay Area. The current forecast has rain coming into the interior Central Coast Saturday morning before spreading northwards into the Bay Area later on Saturday. Light rain and drizzle may start during trick-or-treat hours in the SF Bay Area, but the best chances for rain lie overnight. A low chance for thunderstorms (less than 10% probability) is also present with this system. The conditions might be marginal, but with a cold airmass coming with the upper level low, there might just be enough moisture, instability, and lift to get some convective cells in the higher elevations. K-Index values up to 25-27 degrees C would support isolated to widely scattered thunderstorms. As a final note, high temperatures on Saturday will dip into the middle 60s for the inland valleys, the lower 60s close to the Bays, and the upper 50s to near 60 for the Pacific coast.

The rain will clear out Sunday and Monday as the upper level ridge comes across the West Coast, and highs in the inland valleys will rise to the middle to upper 60s. Beyond that the forecast remains uncertain. The current forecast shows some rain chances returning as early as Tuesday as another trough or cut-off low comes into the region, but the timing of that parent low remains uncertain and ensemble model cluster analysis shows a potential delay of the incoming rain until Wednesday. Rain chances linger through the end of the seven-day outlook, but confidence in any particular scenario remains low heading into the latter part of next week.

Coastal flooding concerns continue across Bayshore locations within the San Pablo, San Francisco, and Monterey Bays through Sunday and the Pacific coastal regions through Saturday. At the San Francisco tidal gauge, high tide is expected to be 1.5 ft above normal (7.3 ft MLLW) at 3:44 PM Saturday, and 1.0 feet above normal (6.8 ft MLLW) at 3:59 PM Sunday, including around 1.5 ft of surge residual.

Aviation

(12Z TAFS) Issued at 437 AM PDT Fri Oct 30 2026

VFR conditions are expected to prevail through a majority of the forecast period, with a slight chance of MVFR ceilings developing early Saturday morning for sites closest to the coast.

Vicinity of SFO: VFR. There is a slight chance of MVFR ceilings developing early Saturday morning, however there is much uncertainty to if/what extent the marine layer will reorganize before another fetch of offshore flow Sunday and Monday.

SFO Bridge Approach: Similar to SFO.

Monterey Bay Terminals: VFR today and tonight with a slight chance of MVFR ceilings late in the forecast period. Similar as above, there is much uncertainty in how well the marine layer can or will reorganize before another fetch of offshore flow Sunday and Monday.

Marine

(Today through Wednesday) Issued at 906 AM PDT Fri Oct 30 2026

Gentle to fresh northwesterly breezes prevail with moderate seas through the weekend. A long period southwesterly swell combines with a long period west-northwest swell early next week.

Watches, warnings and advisories

CA: Coastal Flood Advisory until 6 PM PDT Sunday for CAZ006-506-508- 529-530.

Coastal Flood Advisory until 6 PM PDT Saturday for CAZ505-509.

PZ: None.