FXUS66 KMTR 072334
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
434 PM PDT Wed Oct 7 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1259 PM PDT Wed Oct 7 2026
- Hot inland temperatures continue through Thursday
- Sharp cool-down this weekend
- Coastal flooding and large swell this weekend
- Light rain possible early next week
&&
.SHORT TERM...
Issued at 1259 PM PDT Wed Oct 7 2026
(This evening through Thursday night)
Another hot day. Inland temperatures have already climbed into
the 90s, and the hottest spots will get close to 100 degrees later
this afternoon. At 500 mb a ridge is extending over the Bay Area,
originating from high pressure over the Channel Islands. The 850
mb temperature is 21.5C, which is well above the 90th percentile,
and near the daily max for this time of year. Winds are generally
onshore, which is bringing good relief to the coast, where
temperatures are in the 60s and 70s. As we've seen the last few
days, there is a chance for coastal fog in the morning within a
shallow marine layer.
The ridge will remain in place Thursday, although it will start to
weaken through the day as a cut-off low pressure system approaches
from the west. This will allow the marine layer to expand a bit.
Nevertheless inland temperatures will be broadly similar Thursday,
and the Heat Advisory remains in effect through the day.
&&
.LONG TERM...
Issued at 1259 PM PDT Wed Oct 7 2026
(Friday through next Tuesday)
The long term forecast is quite active. I'll start with a
synoptic breakdown and then list the individual hazards in greater
detail. By Friday the ridge will break down as the cut-off low off
the coast starts to dominate the pattern. This feature will merge
with the jet stream to the north and the remnants of Hurricane
Rachel to the south to form a high amplitude trough over California
through the weekend.
Temperatures: The pattern change will lead to a drastic drop in
temperatures. High temperatures Wed-Thu are 10-20 degrees above
normal for this time of year, and will drop to 5-10 degrees below
normal by Saturday. Friday is the transition with some relief before
the big cool down arrives Saturday. Livermore, for example, has
been dealing with 100+ degree high temperatures since last
Saturday, and we have 72 degrees in the forecast for this
Saturday. That's the good news.
Wind: The incoming trough will bring much lower surface pressure to
California, with a central pressure likely below 1000 mb somewhere
in the Central Valley this weekend. By Saturday, the gradient
between this low pressure and higher pressure over the Pacific will
generate strong to near gale force northwesterly winds across the
coastal waters and along Pacific beaches. These winds will push
inland through gaps and passes as fresh to strong west - southwest
winds Saturday afternoon. We're probably not quite at wind
advisory level, but bring a wind breaker if you're going to Fleet
Week or anywhere near the beach.
Coastal Flooding: With warm waters driven by El Nino, we are seeing
some remarkable tidal anomalies. Every tidal station in the Bay Area
down to Monterey is recording a full foot of residual surge (extra
water above the tide table prediction). With clear skies, light
winds and high pressure, this is caused primarily by thermal
expansion from the warm water. The current sea surface temperatures
are in the low to mid 60s, which is around 5-7 degrees above
normal for this time of year. Beyond the local SST, the regional
waters are quite warm across the Eastern Pacific, especially at
depth. There has been a lot of talk about the 3+ C SST anomaly
from El Nino (a record), but the larger anomaly is found at depth,
closer to the thermocline. In the Nino 3.4 region, the water
temperature at 100 m depth is over 10-13.5C above normal. That's
18-24F. Warmer water takes up more volume through thermal
expansion, and the only place that extra water can go is up. A
Kelvin wave of even warmer water has reached southern California,
where the SSTs are in the 70s and the tidal anomaly is roughly
1.2-1.4 feet above normal. That's heading our way, moving at about
5-10 mph up the coast. All of this extra water will make the
typically innocuous Spring tide driven by a normal new moon feel
more like a King Tide this weekend. The incoming winds and swell
will push the tide even higher. We are expecting high tides this
weekend to be somewhere from 1.2 to 1.5 feet above normal. That's
enough to trigger minor coastal flooding across low-lying areas
in the San Francisco Bay and southern Monterey Bay. This is just a
sign of things to come this season. The extra foot of water will
be here for several months, including during the real king tides
in Nov, Dec, and Jan.
High Surf: In addition to the high tides, there will be large waves
this weekend. This is due to a combination of long period southerly
swell from Hurricane Rachel and large wind waves from the near gale
force conditions over the coastal waters. The forerunners from
Rachel will arrive as early as late Thursday and will build in
height through the weekend. A new set of westerly swell arrives
Sunday from a hurricane force extratropical storm in the central
north Pacific. As the swell reaches the beaches, breaking waves
of 15 feet are possible. Particularly during high tide, these
wave will run much further up the beach and cause erosion. There
will also be stronger currents than normal due to both the large
swell and big tidal swings. Expect a Beach Hazards Statement or
High Surf Advisory to be issued in the next day or two.
Rain: While the moisture from the remnants of Rachel will initially
be confined to the southern California, there is a potential for
some wrap around moisture to bring light rain early next week.
Roughly half of the European ensemble show measurable precip at
SFO Monday-Tuesday, with the ensemble mean around 0.05". None of
the current simulations show anything very impactful.
The cooler weather looks like it will stick around next week, as
the wind and waves calm down.
&&
.AVIATION...
(00Z TAFS)
Issued at 426 PM PDT Wed Oct 7 2026
A shallow marine layer is expected to return again tonight but the
timing of its return along the coast is a bit uncertain. Satellite
imagery shows the marine layer has receded offshore and will
likely take slightly longer to return than initially anticipated.
Have pushed back stratus arrival for MRY and SNS to closer to 06Z.
Stratus arrival for HAF was pushed back as well but confidence is
lower for HAF due to a more substantial stratus push in the
vicinity of HAF on satellite (compared to clear skies near MRY and
SNS). Otherwise, not anticipating stratus/fog to reach interior
airports. High resolution guidance is trying to resolve fog in the
vicinity of SJC overnight but confidence is low given the
relatively dry overnight conditions forecast. Diurnally breezy
onshore winds continue during the afternoon/evening with lighter,
variable to at times offshore winds overnight.
Vicinity of SFO...VFR through the TAF period. Not anticipating
stratus to reach SFO tonight given the shallow nature of the
marine layer. Moderate onshore winds pick up during the late
afternoon/early evening with winds around 18 knots expected before
winds weaken overnight.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Fog/stratus and IFR-LIFR conditions are
expected tonight but the exact timing of stratus return is
slightly uncertain. Pushed the stratus arrival back closer to
06-08Z with models decently resolving the drier airmass
offshore/more substantial recession of stratus offshore near the
Monterey Bay. The latest guidance has stratus filling in over the
bay closer to 06-08Z which contributed to pushing back the arrival
time. Conditions improve by late tomorrow morning with moderate NW
winds expected during the afternoon.
&&
.MARINE...
(Tonight through next Monday)
Issued at 426 PM PDT Wed Oct 7 2026
Gentle to moderate north breezes and moderate seas continue
through Thursday. Strong to near gale force north winds will
develop across the northern outer waters on Friday, spreading
across the rest of the waters this weekend. Rough to very rough
seas will build Friday into the weekend as a result. Long period
southerly swell arrives Friday with long period westerly swell
arriving Sunday, with both long period swells continuing into the
early part of next week.
&&
.FIRE WEATHER...
Issued at 410 AM PDT Wed Oct 7 2026
Hot and dry conditions will lead to elevated fire weather conditions
across the higher terrain through Thursday. Temperatures 10 to 20
degrees above normal and poor minimum relative humidity will
continue away from the compressed marine layer at the coast. The
higher terrain will experience active thermal belting, little-to-no
recovery with nocturnal drying across the highest peaks, and thus
prolonged burn periods. Winds remain the limiting factor, with
diurnal winds prevailing except for light northerly/offshore flow
overnight across the higher terrain. ERC values will rise to near
records during the hot and dry conditions. A pattern change Friday
into the weekend will bring cooler, moister, and windier
conditions.
Sarment
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 9 AM Friday to 3 PM PDT Tuesday for
CAZ006-508-529-530.
Heat Advisory until 10 PM PDT Thursday for CAZ503-504-506-508-
510-512>518.
Coastal Flood Advisory until 4 PM PDT Wednesday for CAZ506.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Kennedy
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Wed Oct 7 18:30:03 PDT 2026
From the National Weather Service
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