Areal Flood Advisory 13, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
239 PM PDT Sun Oct 24 2021

.SYNOPSIS...Moderate to heavy rain in the North Bay today will
shift into the Bay Area through the afternoon. The heavy rain
band will shift over the Santa Cruz Mountains by early evening and
the Central coast tonight. In addition to heavy rain, strong
southerly winds will continue for much of today into this evening.
Rain turns to showers overnight into early Monday. Large
northwest swells arrive Monday with dangerous waves. A chance of
North Bay light rain Tuesday otherwise warming and drying trend.

&&

.DISCUSSION...as of 02:32 PM PDT Sunday...

Through Tonight:

The long scheduled Atmospheric River (AR) event has arrived.
Moderate to heavy rain is ongoing for the North Bay and is moving
into the North and East Bays early this afternoon. This area of
rainfall will continue moving south through the remainder of our
area overnight. Weather-related concerns remain unchanged and we are
monitoring flash flood potential for the 2020 burn scar areas,
street/nuisance flooding for urban areas, and gusty winds area-wide.
This is all to say that it's probably a good idea to stay in today
if you don't have travel plans.

Getting into a little more detail, the main AR should drop south
through the afternoon to early evening hours with several hours of
rain impacting the urban corridors including 101/280 on the
Peninsula and 880/680 on the East Bay. As the AR boundary approaches
the Santa Cruz mountains the focus will then shift to monitoring the
CZU burn scar into this evening for flash flooding potential.
Additionally, 50+ kt winds at ridge top level will create additional
concerns for downed trees and power outages especially for the
higher elevations.

By late evening and before midnight the AR boundary will push into
the hills of coastal Monterey County. The back edge will be abrupt
with rain ending quickly from the north. By midnight rain should
diminish for the Bay area with lingering precipitation overnight
through early tomorrow morning across southern Monterey County.

Monday through Sunday:

Cooler temperatures arrive with a few showers on Monday, with
hazardous marine and beach conditions. A massive northwest swell
from 20-30 feet will hammer the coastline during this time and a
High Surf Advisory is in effect. Be sure to stay well away from the
ocean early next week and stay safe.

Light precipitation may linger into Tuesday for the North Bay as a
weak weather system moves through. Thereafter high pressure should
take hold with dry weather returning.

&&

.AVIATION...as of 10:44 AM PDT Sunday...For the 18z TAFs.
Atmospheric river is in full swing across the North Bay with heavy
rain and MVFR/IFR vis/cigs. Observations show KSTS down to 1.5 SM
vis due to heavy rain with 2 SM all the way down to KSFO. MVFR-IFR
cigs are forecast to persist through mid to late Monday morning
due to rain, low cigs, and low vis. Observations currently have
ceiling heights between 800-2,500 ft for low clouds, 3,500-6,000
ft for mid level clouds, and 10,000 to 15,000 ft for high clouds.
Heavier showers are still expected to move south this afternoon
into the SF Bay/South Bay before reaching the Monterey Bay late
this afternoon/early this evening. Strong winds will also continue
both at the surface (30-40 kt gusts) and aloft where winds of
45-55 kt out of the SW are forecast through late tonight. LLWS
therefore will remain an issue along with gusty SE/SW surface
winds and wet runways. Both surface and winds aloft should
gradually diminish this evening and overnight. Winds are expected
to take a more westerly component tomorrow morning, though some
models have hinted at this happening this evening for certain
locations. Bottom line, poor conditions the rest of today and most
of tonight with heavy rain becoming showers tomorrow.

Vicinity of KSFO...MVFR/IFR conditions are expected to develop by
the afternoon due to low clouds and/or low vis due to heavy rain.
The strongest precipitation is still expected this afternoon into
this evening. Strong southerly surface winds continue with current
observations at the terminal gusting over 40 kt. The AWW remains
in effect until 05z tonight, though latest guidance shows winds
diminishing a little earlier than previously. Will monitor obs and
drop early if possible. Winds look to gradually turn more westerly
overnight, though the HRRR had been suggesting this may happen
earlier. Will monitor obs and adjust the taf as needed. Winds
aloft also remain strong with LLWS expected through late tonight.
Conditions to improve late tonight and tomorrow.

KSFO Bridge Approach...Similar to KSFO.

Monterey Bay...VFR/MVFR ahead of a storm system set to arrive
later this afternoon. Showers remain in the vicinity, but no heavy
rain has been observed thus far at the Monterey Bay terminals.
Cigs should gradually lower ahead of the heavier showers with MVFR
(possibly IFR/LIFR) conditions then persisting through at least
tomorrow morning. Gusty southerly winds also expected with gusts
25-35 kt. Stronger winds aloft are also expected at 40-50 kt thus
resulting in some LLWS through late tonight. Winds should diminish
overnight.

&&

.BEACHES...as of 4:29 AM PDT Sunday...A strong, early season
storm system arrives today and will result in significantly
increased wave energy from late today into early Tuesday. This
wave energy will transition through the coastal waters from late
today into Tuesday, and peak on Monday. Swell of 16 to 24 feet at
16 to 18 seconds is forecast to arrive with the swell train as it
peaks on Monday and result in a number of coastal hazards. These
hazards include large breaking waves of 20 to 30 feet (higher at
favored break points), increased risk of strong longshore and rip
currents, increased risk of coastal erosion and minor coastal
flooding, and enhanced coastal run up concerns due to the summer
beach profiles in place. Due to the early arrival of these large
waves, many beaches are still transitioning from their summer
beach profiles and lack the features and steepness to resist
larger wave run up on coasts. This means that more of this wave
energy will have a chance to move onto the beach and overtake
individuals, potentially injuring them, or pulling them into the
cold ocean. Each year, people die at the coast due to these or
similar ocean conditions. A high surf warning for the entire coast
has been issued for this threat and is in effect from 11PM Sunday
to 11AM Tuesday, with the highest risks once again at west to
northwest facing beaches.

&&

.MARINE...as of 10:05 AM PDT Sunday...A strong storm system
continues to impact the waters with heavy rain, strong winds, and
high seas. Gale force gusts are expected for the entire coastal
waters at some point today including all of the bays. Wind gusts
could strengthen to 40 to 50 kt. These strong winds will generate
very steep swell that result in hazardous conditions, especially
for smaller vessels. Additionally, this system will generate a
large west to northwest swell train with swell heights of 16 to 24
feet at 16 to 18 seconds. Swell heights to peak on Monday and
bring hazardous conditions to the surf zone and near harbor
entrances with breaking waves of 20 to 30 feet.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Wind Advisory...CAZ516>518-528-530
             Flash Flood Watch...CAZ517
             Wind Advisory...CAZ006-508>513-529
             Flash Flood Watch...CAZ509-512
             High Surf Warning...CAZ006-505-509-529-530
             Wind Advisory...CAZ505>507
             GLW...SF Bay until 9 PM
             GLW...Mry Bay until 9 PM
             GLW...Pt Reyes to Pigeon Pt 0-10 nm until 9 PM
             GLW...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             GLW...Pt Arena to Pt Reyes 0-10 nm until 3 PM
             GLW...Pt Arena to Pigeon Pt 10-60 nm until 3 PM

&&

PUBLIC FORECAST: RWW/SPM
AVIATION: AS
MARINE: AS

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1224 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1200 PM     NON-TSTM WND DMG 2 ESE DEL MONTE FOREST  36.58N 121.91W
10/24/2021                   MONTEREY           CA   NWS EMPLOYEE

            TREE DOWN AT MONTEREY COMMUNITY HOSPITAL.

&&

SPM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
201 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0148 PM     FLOOD            2 W ROHNERT PARK        38.35N 122.74W
10/24/2021                   SONOMA             CA   LAW ENFORCEMENT

            STREET FLOODING AT INTERSECTION OF ROHNERT
            PARK EXPWY AND STONY POINT RD.

&&

JL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
214 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0154 PM     NON-TSTM WND DMG 8055 FERNWOOD AVE       37.07N 122.08W
10/24/2021                   SANTA CRUZ         CA   LAW ENFORCEMENT

            TREE DOWN, HIT RPS GARAGE AND ANOTHER
            STRUCTURE.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
217 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0131 PM     NON-TSTM WND DMG 2 SSW LEXINGTON HILLS   37.14N 121.99W
10/24/2021                   SANTA CRUZ         CA   LAW ENFORCEMENT

            TREE DOWN BLOCKING ROAD WAY.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
311 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0255 PM     NON-TSTM WND DMG GRAHAM HILL RD          37.01N 122.03W
10/24/2021                   SANTA CRUZ         CA   PUBLIC

            TREE DOWN 1125 NB LNS.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
325 PM PDT SUN OCT 24 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0308 PM     NON-TSTM WND DMG SCENIC WY               36.97N 122.05W
10/24/2021                   SANTA CRUZ         CA   PUBLIC

            LARGE TREE DOWN 1125 LN OF TRAFF.

&&

ED