Marine Weather and Tide Forecast for Diablo Grande, CA

UPDATE
Issued at 826 PM PDT Mon Sep 21 2026

Stratus is expanding across the inland valleys in the wake of the cut-off low, which is moving across the southern part of the Central Valley into the Mojave Desert. Coastal drizzle was reported in the late afternoon hours, and will be added to the forecast through the night with the upcoming forecast package. No other changes to the forecast.

DialH

SHORT TERM
Issued at 1120 AM PDT Mon Sep 21 2026 (This afternoon through Tuesday)

The dominant weather feature today is a 500 mb cut-off low currently centered over Pt. Conception. The 500 mb height at Vandenberg was 5750m as measured from the 12Z sounding. This is just below the 10th percentile in the climatology for this time of year, so it's fairly notable, but not extreme. The result is cooler temperatures, a deeper marine layer, some morning drizzle, and even a few real raindrops. The marine layer was measured at 2,400 feet deep by the 12Z weather balloon from Oakland. This deeper cloud layer, combined with low-level vorticity and orographic lift allowed some coastal drizzle this morning. Drizzle was reported throughout the typical areas across the Bay Area and Central Coast. The La Honda RAWS in the Santa Cruz Mountains was the winner with 0.05" of precipitation recorded over the last 24 hours. This deep marine layer, high humidity and ample cloud cover will keep temperatures 5-10 degrees cooler than normal this afternoon.

The cut-off low will continue to slide NE over the next 24 hours, loosening its grip on the weather here. Tuesday will be a transition day as the marine layer starts to compress and temperatures increase back to normal.

LONG TERM
Issued at 1120 AM PDT Mon Sep 21 2026 (Tuesday night through next Sunday)

The long term forecast is a little bit of a roller coaster, but like the kind for kids that doesn't do anything too scary. As the low continues to exit the area, the upper level pattern will gradually shift to a strong trough over the Gulf of Alaska and a ridge stretching from Texas to central Canada. By Wednesday the west coast will be in between these two features, with a small positive 500 mb height anomaly arriving Wednesday. While the 500 mb height anomaly is minor, the 850 temperature anomaly will climb to around 5-7C above normal Wednesday - Thursday. This will bring inland temperatures into the upper 80s to low 90s, with 70s along the coast both Wednesday and Thursday. There is some moderate HeatRisk associated with this event, but it's not widespread and has been trending down. With the longer nights, short duration, and continued onshore winds, we are not expecting a heat advisory with this event at this time. The trough over the Gulf of Alaska will move into the Pacific Northwest by Friday, reversing the warming trend and bringing temperatures back below normal for next weekend.

AVIATION
(00Z TAFS)
Issued at 457 PM PDT Mon Sep 21 2026

Marine layer remains entrenched along the coast and locally inland already as of 00z and will spread inland efficiently and early this evening with a trough over the region. Low cigs to linger at least through 18-19z Tuesday before mixing out.

Vicinity of SFO...Low cigs to push over the terminal early this evening, as early as 03z then linger at least through 18-19z Tuesday.

SFO Bridge Approach...Stays clear through around 04z before losing visuals through at least 17z Tuesday.

Monterey Bay Terminals...KMRY and KSNS already have ceilings and high confidence they continue at least through 18-19z Tuesday.

MARINE
(Tonight through next Sunday)
Issued at 826 PM PDT Mon Sep 21 2026

Moderate to fresh northwest breezes persist overnight with locally stronger winds north of Point Reyes. By Tuesday afternoon, widespread strong northwest winds prevail across the coastal waters, allowing for seas to build from moderate to rough.
Northwest winds and seas remain elevated through the week with a brief period of improved conditions Wednesday night into Thursday.
By Friday, winds increase with building rough seas.

FIRE WEATHER
Issued at 423 AM PDT Mon Sep 21 2026

An upper-level low will support near to slightly below normal temperatures, increased diurnal winds, a deep (2,500') marine layer. Warming and drying trend kicks off Tuesday with temperatures up to 10 degrees above normal and areas of moderate HeatRisk Wednesday and Thursday. The marine layer will compress below 1,000 feet during this warm-up with nocturnal drying expected above it.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 3 PM to 9 PM PDT Tuesday for Pigeon Pt to Pt Pinos 0-10 nm.

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

Small Craft Advisory from 3 PM Tuesday to 5 AM PDT Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.