542
FXUS66 KMTR 031802
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1102 AM PDT THU SEP 3 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1010 PM PDT WED SEP 2 2026
- BENEFICIAL RAIN THURSDAY, MAINLY IN THE NORTH BAY
- HAZARDOUS BEACH CONDITIONS THIS WEEKEND
SHORT TERM
ISSUED AT 1010 PM PDT WED SEP 2 2026
(TONIGHT THROUGH FRIDAY)
THE MARINE LAYER IS GONE. A COLD FRONT IS CURRENTLY LOCATED ABOUT
200 MILES WEST OF SAN FRANCISCO AND IS SUPPORTED IN THE UPPER LEVELS
BY A 500 MB TROUGH AND A MERIDIONAL JET STREAM. WE SAW SOME PRE-
FRONTAL RAIN IN THE NORTH BAY ON WEDNESDAY. SANTA ROSA RECEIVED
0.08" AND MT. TAM RECORDED 0.64". THAT WAS JUST THE WARM-UP. THE
MAIN EVENT WILL OCCUR THURSDAY MORNING AS THE FRONT MOVES THROUGH.
MODELS HAVE BEEN TRENDING WETTER, AND WE'RE NOW EXPECTED AROUND 1/4"
IN SANTA ROSA THROUGH THE MORNING AND UP TO 1" IN THE MOUNTAINS.
THAT'S NOT ENOUGH TO CAUSE ANY MAJOR ISSUES, BUT IT IS REAL RAIN,
ESPECIALLY FOR THIS TIME OF YEAR. THE NORMAL RAINFALL FOR THE
ENTIRE MOTH OF SEPTEMBER IS 0.15" AT SANTA ROSA. EXPECT SLICK
ROADWAYS IN THE NORTH BAY THURSDAY MORNING.
AS THE FRONT CONTINUES TO MARCH SOUTH, THE ASSOCIATED RAIN SHOULD
CROSS THE GOLDEN GATE BY MIDDAY, BUT IT WILL BE LOSING UPPER LEVEL
SUPPORT AND START TO RAPIDLY WEAKEN. WHILE A GOOD PORTION OF THE
BAY AREA SHOULD SEE SOME RAIN, IT LIKELY WON'T BE MORE THAN A FEW
HUNDREDTHS OUTSIDE OF THE COASTAL MOUNTAINS. THE CENTRAL COAST
WILL BE EVEN DRIER, AND WILL HAVE TO WAIT UNTIL THURSDAY EVENING
TO SEE IF ANY RAIN WILL FALL.
IN ADDITION TO RAIN, THIS FRONT WILL BRING NW WINDS WITH GUSTS UP TO
25 MPH FOR MOST. STRONGER GUSTS OF 30-40MPH ARE EXPECTED THROUGH
FAVORED GAPS/PASSES, AND IN THE SALINAS VALLEY. WE'LL OBVIOUSLY HAVE
MORE CLOUD COVER THURSDAY AS WELL, KEEPING THE TEMPERATURES COOL
AND COMFORTABLE.
AFTER THE FRONT PASSES, SKIES WILL CLEAR FROM NORTH TO SOUTH THROUGH
THURSDAY EVENING. AS THE SKIES CLEAR, RADIATIONAL COOLING OVERNIGHT
WILL HELP THE MARINE LAYER WILL START TO REFORM. WHILE THERE IS
STILL SOME UNCERTAINTY WITH THE TIMING, MARINE LAYER STRATUS WILL
LIKELY RETURN TO THE NORTH BAY BY FRIDAY MORNING, BUT MAY TAKE UNTIL
SATURDAY OR EVEN SUNDAY TO REACH THE CENTRAL COAST.
LONG TERM
ISSUED AT 1010 PM PDT WED SEP 2 2026
(FRIDAY NIGHT THROUGH NEXT WEDNESDAY)
SPEAKING OF THIS WEEKEND, A BEACH HAZARDS STATEMENT IS IN EFFECT
FROM FRIDAY THROUGH MONDAY AS SOUTHERLY SWELL FROM MULTIPLE DISTANT
HURRICANES REACHES THE COAST. DAYS WHEN IT'S NICE OUTSIDE BUT THE
OCEAN IS ENERGETIC ARE TYPICALLY THE MOST DEADLY. ON TOP OF THAT
IT'S A HOLIDAY WEEKEND. PLEASE REFER TO THE BEACHES SECTION BELOW
FOR MORE DETAILS.
BEHIND THE FRONT THE TEMPERATURE OUTSIDE OF THE NEWLY FORMING MARINE
LAYER WILL START TO WARM UP THROUGH THE WEEKEND. AT 500 MB THE
TROUGH OVER THE COAST WILL BECOME A PSEUDO CUT-OFF LOW. WHILE IT
DETACHES FROM THE 500 MB FLOW, A HEALTHY JET FINGER WILL CONTINUE TO
PROVIDE SOME UPPER LEVEL DIVERGENCE THROUGH THE WEEKEND.
NEVERTHELESS THE LOW PRESSURE WILL GRADUALLY FILL. MEANWHILE HIGH
PRESSURE OVER THE SOUTHWEST WILL START TO INFLUENCE THE WEATHER,
ALLOWING TEMPERATURES TO REBOUND BACK TO NORMAL BY MONDAY.
AS HURRICANE MARIE NOW LOOKS LIKE IT WILL TAKE A MORE WESTERLY TRACK
OUT TO SEA, THE RESIDUAL MOISTURE IMPACTS ARE MUCH LESS LIKELY TO
REACH ANY FURTHER NORTH THAN SOUTHERN CALIFORNIA THIS WEEKEND.
MODELS ARE ALSO SHOWING A SLUG OF DRY AIR SUNDAY OVER THE CENTRAL
COAST THAT BLOCKS THE LESS DENSE TROPICAL AIR MASS FROM MOVING
NORTH. THE DETERMINISTIC ECMWF SHOWS 1.8" OF PW AT LOS ANGELES
SUNDAY AFTERNOON, WHILE MONTEREY HAS 0.5". THAT WOULD GIVE
SOUTHERN CALIFORNIA A DECENT AMOUNT OF RAIN, BUT NOTHING FOR THE
BAY AREA. IT'S A SIMILAR STORY WITH INSTABILITY. NOT A SINGLE
MEMBER OF THE ECMWF ENSEMBLE HAS MUCAPE OVER 50 J/KG NORTH OF PT.
CONCEPTION. THERE IS ALWAYS THE CHANCE THAT THE TROPICAL MOISTURE
RIDES OVER THIS DRY AIR MASS, OPENING THE DOOR FOR DRY
THUNDERSTORMS. THERE'S NO DIRECT SUPPORT FOR THAT IN THE MODEL
GUIDANCE AT THE MOMENT, BUT PATTERN RECOGNITION SUGGESTS IT'S
WORTH KEEPING AN EYE ON.
WHILE THIS WEEKEND NOW LOOKS LIKE IT WILL PROBABLY BE DRY, THERE IS
A HINT IN THE GUIDANCE THAT THE REMNANTS OF MARIE WILL EVENTUALLY
GET CAUGHT UP IN THE PERSISTENT SW FLOW IF THE CUT-OFF LOW CAN
SURVIVE LONG ENOUGH. IF THAT HAPPENS, WE MAY SEE SOME ASSOCIATED
MOISTURE BY THE MIDDLE OF NEXT WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1101 AM PDT THU SEP 3 2026
INLAND TERMINALS ARE MOSTLY VFR WITH SUB-MVFR CONDITIONS ACROSS THE
NORTH BAY AND NEAR THE COAST AS A WEAK FRONTAL BOUNDARY APPROACHES
THE REGION. THE GREATEST POTENTIAL FOR -RA WILL BE AT KSTS THIS
MORNING AND THROUGH EARLY AFTERNOON BEFORE THE BOUNDARY SAGS
SOUTHWARD THROUGHOUT THE AFTERNOON AND EARLY EVENING. -RA IS ALSO
POSSIBLE AT TERMINALS TO THE SOUTH, BUT LITTLE TO NO MENSURABLE
RAINFALL IS EXPECTED SOUTH OF THE GOLDEN GATE. ONSHORE WINDS WILL
INCREASE A BIT THIS AFTERNOON IN WAKE OF THE FRONTAL PASSAGE WITH
VFR CONDITIONS RETURNING. TONIGHT, THE MARINE LAYER IS FORECAST TO
DEEPEN TO AROUND 2000 FEET AND WILL SEE MVFR CIGS ALONG THE COAST
WITH THE POTENTIAL FOR SUB-MVFR CIGS EARLY FRIDAY MORNING. VFR
CONDITIONS ARE ANTICIPATED AFTER OR AROUND 18Z FRIDAY.
VICINITY OF SFO...VFR. ONSHORE WINDS ARE FORECAST TO INCREASE THIS
AFTERNOON AND EARLY EVENING IN WAKE OF THE FRONTAL PASSAGE WITH
GUSTS UP TO 20 KT. THERE IS THE POTENTIAL FOR MVFR CONDITIONS AS THE
FRONT PASSES THROUGH BETWEEN 20Z THURSDAY-03Z FRIDAY. WINDS EASE
SLIGHTLY AFTER SUNSET. THERE IS GREATER CONFIDENCE FOR MVFR CIGS (40-
60% PROBABILITY) TO DEVELOP EARLY FRIDAY MORNING AND PERSIST THROUGH
16Z FRIDAY BEFORE LIFTING TO VFR. NORTHWESTERLY WINDS ONCE AGAIN
INCREASE FRIDAY AFTERNOON.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. ONSHORE WINDS ARE FORECAST TO INCREASE
THIS AFTERNOON AND EARLY EVENING. THE FRONTAL BOUNDARY IS FORECAST
TO GRADUALLY DISSIPATE AS IT APPROACHES THE REGION LATE TONIGHT AND
INTO EARLY FRIDAY MORNING. AS SUCH, EXPECTING MVFR CONDITIONS TO
DEVELOP BY LATE EVENING AND LOWER TO IFR (40-60% PROBABILITY) INTO
EARLY FRIDAY MORNING. THERE IS LESS THAN 10-30% CHANCE OF REACHING
LIFR CONDITIONS BETWEEN 08-15Z FRIDAY, HOWEVER HAVE LEFT OUT OF THE
CURRENT TAF PACKAGE. VFR CONDITIONS ARE ANTICIPATED AFTER OR AROUND
18Z FRIDAY.
MARINE
(TODAY THROUGH TUESDAY)
ISSUED AT 1101 AM PDT THU SEP 3 2026
RAIN CHANCES INCREASE OVER THE NORTHERN WATERS THROUGH THE DAY AS
A WEAK COLD FRONT MOVES THROUGH THE REGION. SOUTHWESTERLY WINDS
GRADUALLY SHIFT NORTHWESTERLY BY THIS AFTERNOON AFTER COLD FRONTAL
PASSAGE. WINDS GENERALLY STAY GENTLE TO MODERATE BUT DIURNAL
FRESH TO STRONG GUSTS RETURN WITHIN THE MONTEREY BAY AND ALONG THE
BIG SUR COAST FRIDAY INTO THE WEEKEND. MORE WIDESPREAD FRESH TO
STRONG GUSTS RETURN BY EARLY NEXT WEEK ACROSS THE COASTAL WATERS.
LONG PERIOD SOUTHERLY SWELL ASSOCIATED WITH TROPICAL ACTIVITY WELL
TO OUR SOUTH WILL REACH THE COASTAL WATERS FRIDAY AND CONTINUE
INTO EARLY NEXT WEEK.
BEACHES
ISSUED AT 1010 PM PDT WED SEP 2 2026
A BEACH HAZARDS STATEMENT IS IN EFFECT FRIDAY-MONDAY AS THE SWELL
FROM BOTH HURRICANE MARIE AND HURRICANE KARINA REACHES THE COAST.
AS THESE HURRICANE WHIP UP THE OCEAN, THE WAVES TRAVEL OVER 1,000
MILES IN ALL DIRECTIONS, GRADUALLY FLATTENING OUT TO LOW
AMPLITUDE, BUT LONG PERIOD SWELL. THESE WAVES AREN'T VERY
INTIMIDATING IF YOU'RE ON A BOAT IN THE OPEN OCEAN, BUT THE LONG
PERIOD ALLOWS THEM TO PUSH MUCH FARTHER UP THE BEACH. LONG PERIOD
SWELL ALWAYS INCREASES THE CHANCE FOR SNEAKER WAVES, BUT THAT'S
PARTICULARLY TRUE THIS WEEKEND SINCE THERE ARE 2 DIFFERENT SETS OF
SOUTHERLY SWELL, AND THEIR ENERGY WILL PERIODICALLY COMBINE. IN
ADDITION TO SNEAKER WAVES, EXPECT STRONG RIP CURRENTS AND
BREAKING WAVES UP TO 10 FT. AS THIS IS A HOLIDAY WEEKEND AND THE
WEATHER IS OTHERWISE PRETTY NICE, THE EXPOSURE TO THE RISK IS
HIGH. AVOID THE WATER IF YOU'RE NOT AN EXPERT SWIMMER. IF CAUGHT
IN A RIP CURRENT, SWIM PARALLEL TO SHORE UNTIL YOU STOP FEELING
THE PULL. EVEN ON THE BEACH, BE PREPARED FOR SNEAKER WAVES THIS
WEEKEND AND NEVER TURN YOUR BACK ON THE OCEAN.
MTR WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT FROM FRIDAY MORNING THROUGH MONDAY
EVENING FOR CAZ006-505-509-529-530.
PZ...SMALL CRAFT ADVISORY UNTIL 5 PM PDT THIS AFTERNOON FOR SF BAY N
OF BAY BRIDGE.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...RGASS
MARINE...RGASS
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