San Francisco Bay South of the Bay Bridge Marine Forecast
|Tonight...W Winds 10 To 15 Knots With Gusts Up To 25 Knots... Diminishing To 5 To 10 Knots After Midnight.|
|Fri...W Winds 15 To 20 Knots With Gusts Up To 25 Knots.|
|Fri Night...W Winds 10 To 15 Knots. A Chance Of Rain.|
|Sat...W Winds 10 To 15 Knots. A Chance Of Rain.|
|Sat Night...Sw Winds 5 To 10 Knots.|
|Sun...Sw Winds 5 To 10 Knots.|
|Sun Night...Sw Winds 5 To 10 Knots.|
|Mon...W Winds 5 To 10 Knots.|
|Tue...W Winds 5 To 10 Knots.|
| Area Forecast Discussion|
National Weather Service San Francisco CA 508pm PDT Thu September 28 2023
.SHORT TERM... (This evening through Friday) Issued at 124pm PDT Thu September 28 2023
Clear skies abound once again today as the atmosphere remains well- mixed around the base of a deep upper trough. Highs this afternoon running right about normal for most, slightly below normal along the coast. A change is in store for tomorrow with the deep trough digging southward across CA. Evident on satellite currently up in Oregon and off the coast of northern CA, more extensive cloud cover will begin to affect our area midday into the afternoon hours tomorrow. As such, a slight cool down in temps can be expected. Gusty winds generally 25-30 mph will spread across the area before the arrival of the surface cold front during the afternoon. Scattered rain showers will gradually spread southward through the evening hours. Rain chances begin to increase during the evening and overnight hours Friday, but most of the rain is expected to fall into Saturday morning. More detail in the long term discussion below.
(Friday night through next Wednesday) Issued at 1232pm PDT Thu September 28 2023
Friday Night through Sunday:
A meridional flow pattern will exist aloft featuring a sharpening trough across the Western CONUS and amplified ridging over the eastern Pacific. An occluding surface low attendant to the upper feature should trek along the northern/central CA coast late Friday night into Saturday with an associated surface front moving onshore. This should provide sufficient lift for light to occasionally moderate rain showers to push south through the region during this timeframe. While rain amounts shouldn't be overly impressive (generally below 0.25 inches for most), this looks to be the first widespread wetting rainfall this season for much of the inland Bay Area and Central Coast. Sufficient instability also exists across mainly inland Monterey and San Benito Counties for a thunderstorm or two to develop, although potential and confidence are low (10-15% range) at this time. If an isolated storm did develop it would be of the wet variety. Outside of rain chances breezy onshore winds are expected along the coastal interface, within the higher terrain, and through the favorable gaps and passes. These winds should remain below Wind Advisory thresholds (which require 45+ gusts in the lower elevations) but will be breezy nevertheless. Temperatures will be on the cool side given clouds and precipitation with highs mostly in the 60s to lower 70s. Lows should generally be in the 50s.
Sunday Night through Thursday:
The upper trough will depart to our east early in the period thus allowing eastern Pacific high pressure to nose in through mid week. There may be a quick burst of northerly (drying) winds across eastern Napa County late Saturday night into Sunday morning. At this point the duration of any gusty/drying conditions appears rather short and this would be following potential precipitation on Saturday. So for now it does not appear to be a particularly great fire weather concern but trends will be monitored. Looking forward, the upper ridge may lose some influence by late week as some weak perturbations trek north through the region. However the most likely forecast outcome suggests dry and quiet weather for the end of the work week.
(Today through Tuesday) Issued at 243am PDT Thu September 28 2023
Northwesterly winds continue to strengthen, with gales beginning to develop over much of the outer waters and coastal jet regions. Gales last through much of the day today, then weakening towards late Friday morning to become fresh. Northwest swell continues to diminish, though large wind waves build overnight tonight and persist through the weekend. Both winds and waves will combine to create dangerous conditions for small craft through the remainder of the week. Chances of rain approach towards Saturday evening with the arrival of a new low pressure system.
NOAA San Francisco Bay Area Office: Watches - Warnings - Advisories
CA...None. PZ...Small Craft Advisory from 9am Friday to 3am PDT Saturday for PZZ530.
Small Craft Advisory until 9pm PDT this evening for PZZ535.
Small Craft Advisory from 9am to 9pm PDT Friday for PZZ535.
Gale Warning until 3am PDT Friday for PZZ540-570-575.
Gale Warning until 9pm PDT this evening for PZZ545-560.
Gale Warning until 4pm PDT Friday for PZZ565.