FXUS66 KMTR 081709
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1009 AM PDT Tue Sep 8 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1130 PM PDT Mon Sep 7 2026

  - Warming and drying trend will bring widespread moderate to 
    major HeatRisk through Thursday

&&

.UPDATE...
Issued at 927 AM PDT Tue Sep 8 2026

Want to emphasize that today will begin a warm-up that will peak
tomorrow, then moderate somewhat on Thursday with temperatures
closer to normal by Friday into the weekend. Even though todays
heat may not reach the level or extent necessary for an advisory,
it will still feel warmer than normal across much of our area,
including much our coastal areas that are experiencing a weak 
fetch of offshore flow. Another factor adding to the heat concerns
tomorrow and Thursday, is the amount of moisture advecting north 
with the remnants of Marie. Not only will we see higher 
temperatures, we'll see less relief overnight with the higher 
dewpoints and higher relative humidity levels during peak heating 
Wednesday and Thursday, further complicating heat impacts. 
Remember to never leave people or pets in the car, take plenty of 
breaks and seek shade/AC shelter if working outside and drink 
plenty of people.

&&

.SHORT TERM...
Issued at 1151 PM PDT Mon Sep 7 2026
(Tonight through Wednesday)

24 hour trends are warmer and drier. Already a warming trend is 
underway with increasing thermal and height ridging aloft. Any
marine layer influence is confined to within a few hundred feet 
of sea level with only a few patches of fog along the Big Sur 
coast at the moment.

The large scale pattern shift to warmer/hotter temperatures 
involves both the retrogression (westward motion) of the 
subtropical ridge over the central U.S. and the eventual merging 
of tropical energy and moisture from steadily decaying TS Marie 
and a cut-off low far to our west (also forecast to retrogress). 
Strengthening 500 mb heights, large scale compression and the Sep 
sun angle will raise temperatures up further Tuesday, peaking well
above normal both Wednesday and Thursday. A little bit of a 
wildcard to this week's pattern is the northward intrusion of 
tropical moisture including some warm air advection (far from 
decaying TS Marie) which will be west of the 500 mb ridge axis. 
Higher to much higher precipitable water will arrive here, model 
forecasts are still showing near 1.40" in the Bay Area mid-week, 
near the max moving average for Oakland upper air early-mid Sep 
climatology. Mid and high clouds will increase, but we don't 
really know quite yet with high confidence how well the models may
or may not be handling mid-level convective potential (mucape) 
with disagreement among various output from e.g. from the HRRR and
GFS. Good to see the GFS shows very minimal to no mucape anyhow. 
Also, with hotter surface temperatures (greater internal energy) 
air parcels will stay capped as long as the atmosphere is stable.

Hot temperatures for this week are not quite in reach of long term
record highs at this point, except Half Moon Bay may get close if
there's no shallow sea breeze mid-week as an offset to the 
temperature. Will continue to monitor.

A Heat Advisory is in effect for the entire forecast area from 10
AM Wednesday to 10 PM Thursday. We've had a nice 10 to 11 day run
of below normal temperatures (due to a large scale trough), 
especially inland, so the sudden reversal in temperatures will be 
noticeable if not already. With widespread moderate to major 
HeatRisk, this affects most individuals sensitive to heat, 
especially those without effective cooling and/or adequate 
hydration. Please stay out of direct sunlight, and stay properly
hydrated. Hot conditions can cause heat illnesses.

Also, minor coastal flooding is likely within a small window of 
time of about 1 hour nearest high tide Tuesday (possibly Wednesday
as well) for bayshore locations of Marin County. Impacts will 
include minor flooding of the lowest lying areas directly along 
the shoreline. At the San Francisco tidal gauge, high tide is 
expected to be 1 ft above normal at 9:59 PM 9/8. At this time we 
are messaging it here and will include messaging in social media 
vs issuing a coastal flood advisory for Tuesday.

The Beach Hazards Statement was allowed to expire.

&&

.LONG TERM...
Issued at 1151 PM PDT Mon Sep 7 2026
(Wednesday night through next Monday)

Well above normal hot weather continues Thursday. Thereafter
northwest winds and a gradual weakening of the 500 mb ridge will
bring a cooling trend for late in the week and weekend. Daytime
highs will cool back to near normal Friday, then possibly a few
degrees below normal for the upcoming weekend. Late week weather
will be dry with the mid-latitude pattern settling back in.

&&

.AVIATION...
(18Z TAFS)
Issued at 958 AM PDT Tue Sep 8 2026

Currently VFR at all terminals with stratus along the Big Sur 
Coast and high clouds streaming in from the southwest. High 
confidence in VFR through the TAF period, the only exception would
be if an eddy formed in the Monterey Bay or stratus developed off 
the San Francisco Peninsula Coast. If clouds are able to form, 
ceilings and visibilities would be LIFR. Diurnal winds will 
prevail with a later than normal arrival of the sea breeze in the 
afternoon. Winds will be light and likely variable overnight, 
favoring terrain.

Vicinity of SFO...Currently VFR with light northeasterly flow.
High confidence in VFR through the TAF period. Diurnal winds will
prevail with a later than normal arrival of the sea breeze this
afternoon. Winds overnight may be light and variable, but will
likely favor a northeasterly direction.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with northwesterly flow at
MRY and VFR with drainage flow at SNS. Moderate to high confidence
in VFR prevailing through the TAF period, only exception would be
if an eddy is able to develop within the Bay. Diurnal winds will
prevail with a later than normal arrival of the sea breeze this
afternoon with drainage winds tonight.

&&

.MARINE...
(Today through Sunday)
Issued at 927 AM PDT Tue Sep 8 2026

A gentle to moderate northwesterly breeze will prevail through
Wednesday, increasing to become fresh to strong Thursday afternoon
into the weekend. Slight to moderate seas will prevail, building
to become rough in the outer waters Friday into Saturday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 8 PM this evening to 1 AM PDT 
     Thursday for CAZ006-506-508-529-530.

     Heat Advisory from 10 AM Wednesday to 10 PM PDT Thursday for 
     CAZ006-502>506-508>510-512>518-528>530.

PZ...None.
&&

$$

SHORT TERM...Canepa
LONG TERM....Canepa
AVIATION...Sarment
MARINE...Sarment

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Prepared by Boulder-Creek.com Weather at: Tue Sep 8 12:30:03 PDT 2026