588
FXUS66 KMTR 311900
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1200 PM PDT MON AUG 31 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1004 PM PDT SUN AUG 30 2026
- MORNING DRIZZLE LIKELY ALONG THE COAST
- COOLER WEATHER CONTINUES THIS WEEK
- CHANCE FOR LIGHT RAIN WED-THU IN NORTH BAY
SHORT TERM
ISSUED AT 1004 PM PDT SUN AUG 30 2026
(TONIGHT THROUGH TUESDAY)
MARINE LAYER STRATUS IS BECOMING MUCH BETTER ORGANIZED THAN 24
HOURS AGO. LOW CLOUDS NOW COVER THE ENTIRE COAST SOUTH OF PT.
REYES. WITH A DEEPER, MORE ORGANIZED MARINE LAYER, HIGH
RESOLUTION MODELS ARE SUGGESTING COASTAL DRIZZLE IS LIKELY MONDAY
AND TUESDAY MORNING.
THE TROUGHING PATTERN WILL DEEPEN OVER THE NEXT 48 HOURS, KEEPING
HIGH TEMPERATURES 5-15 DEGREES BELOW NORMAL FOR THIS TIME OF YEAR.
ACCORDING TO THE ECMWF ENSEMBLE, THERE IS AN 90% CHANCE THE 850
MB TEMPERATURE WILL DROP BELOW 12 C ON TUESDAY, WHICH IS THE
BOTTOM 10TH PERCENTILE FOR THIS TIME OF YEAR. AS THE TROUGH AXIS
APPROACHES THE COAST, THERE IS A GOOD CHANCE (ROUGHLY 70%) THAT
THE NORTH BAY WILL GET SOME LIGHT RAIN STARTING TUESDAY.
LONG TERM
ISSUED AT 1004 PM PDT SUN AUG 30 2026
(TUESDAY NIGHT THROUGH NEXT SUNDAY)
THE JET STREAM BECOMES HIGHLY MERIDIONAL (NORTH TO SOUTH) BY
WEDNESDAY. THIS MAKES THE FORECAST MORE CHALLENGING. THE 500 MB
LOW WILL LINGER AROUND THE PACIFIC NORTHWEST, BUT THE EXACT TRACK
BECOMES MUCH LESS CERTAIN, AND THE MODELS ARE SPLIT IF IT WILL
BECOME COMPLETELY CUT-OFF FROM THE JET STREAM LATER THIS WEEK OR
NOT. EITHER WAY THE COOLER WEATHER AND OCCASIONAL LIGHT RAIN
CHANCES WILL CONTINUE THROUGH THE REST OF THE WEEK. THE EXACT EVOLUTION
OF THIS LOW COULD HAVE A MAJOR IMPACT ON THE WEATHER NEXT WEEKEND
AND BEYOND.
FIRST SOME BACKGROUND. THERE IS AN TROPICAL DISTURBANCE IN THE
EASTERN PACIFIC WELL OFFSHORE SW MEXICO. THE NATIONAL HURRICANE
CENTER IS CURRENTLY CALLING THIS SYSTEM INVEST AREA 95E AS THEY
MONITOR FOR THE FURTHER DEVELOPMENT NEEDED TO EARN A NAME. THIS
SYSTEM HAS A 90% CHANCE OF FORMATION INTO A TROPICAL DEPRESSION IN
THE NEXT 48 HOURS, AND HAS A HIGH CHANCE OF BECOMING A HURRICANE
BY MID-WEEK. THIS WOULD BE THE 13TH TROPICAL CYCLONE IN THE
EASTERN PACIFIC THIS SEASON, SO WHY AM I WRITING ABOUT IT?
TROPICAL CYCLONES ARE STEERED BY LARGE SCALE, MID-TROPOSPHERIC
PRESSURE SYSTEMS. TYPICALLY THE SEMI-PERMANENT HIGH PRESSURE OVER
THE SUBTROPICAL EASTERN PACIFIC BLOCKS TROPICAL CYCLONES FROM
LEAVING THE DEEP TROPICS. THEY VERY OFTEN RIDE THE TRADE WINDS AND
FOLLOW A WNW TRACK AFTER FORMING, MOVING INTO THE OPEN OCEAN.
WITH THE DEEP TROUGH OVER THE WEST COAST BREAKING UP THE TYPICAL
PATTERN, THE DOOR IS OPEN FOR THIS PARTICULAR TROPICAL CYCLONE TO
TAKE A MORE NORTHERLY TRACK, ROUGHLY PARALLEL TO THE COAST OF
MEXICO.
TO BE CLEAR, THERE IS VIRTUALLY NO CHANCE THAT A HURRICANE WILL
MAKE LANDFALL IN CALIFORNIA. WHILE IT'S TRUE THE SST ANOMALIES
ARE QUITE HIGH (3-5 F) ALONG THIS TRACK, THE ACTUAL WATER
TEMPERATURE (70-74 F) IS STILL FAR TOO COLD TO SUPPORT A
TROPICAL CYCLONE NORTH OF THE VIZCAINO PENINSULA (MID BAJA).
HOWEVER, IF THE CUT-OFF LOW STAYS STRONG ENOUGH, AND MOVES FAR
ENOUGH SOUTH TO PULL THE TROPICAL CYCLONE QUICKLY TO THE NORTH,
THERE COULD BE IMPACTS FROM THE REMNANTS OF THIS SYSTEM IN ABOUT A
WEEK. THE PRIMARY IMPACTS WOULD BE RAIN AND WIND, AND THEY WOULD
LIKELY BE FOCUSED ACROSS SOUTHERN CALIFORNIA. THERE ARE SO MANY
MOVING PUZZLE PIECES THAT IT'S IMPOSSIBLE TO BE MORE SPECIFIC AT
THIS TIME, BUT THE CHANCE IS THERE, AND WE'LL KEEP AN EYE ON IT.
AVIATION
(18Z TAFS)
ISSUED AT 1156 AM PDT MON AUG 31 2026
FINISHING FOGUST OFF STRONG WITH A ROBUST MARINE LAYER AT A DEPTH OF
AROUND 2200 FEET THIS MORNING. MVFR STRATUS WILL TAKE A BIT LONGER
TO SCATTER OUT TODAY, LIKELY IN THE EARLY AFTERNOON. MODERATE
ONSHORE WINDS INCREASE THROUGH THE DAY AND EASE SLIGHTLY OVERNIGHT.
APC AND LVK MAY EXPERIENCE GUSTS UP TO 20 KT THROUGH THE LATE
AFTERNOON WHICH WILL GRADUALLY DIMINISH TONIGHT. MEDIUM CONFIDENCE
ON HOW WIDESPREAD THE MARINE LAYER WILL BE TONIGHT AS AN UPPER LEVEL
TROUGH APPROACHES OUR COAST. THIS TROUGH MAY GENERATE SUFFICIENT
LIFTING TO MIX OUT THE MARINE LAYER ACROSS THE NORTH BAY, BUT
CONFIDENCE REMAINS LOW. HIGHER CONFIDENCE FOR COASTAL SITES TO
DEVELOP MVFR CEILINGS AROUND SUNSET WITH HAF LIKELY TO STAY CLOUDY
ALL DAY.
VICINITY OF SFO...MVFR STRATUS PERSISTS INTO THE AFTERNOON AS
MODERATE WESTERLY WINDS INCREASE. THERE HAS BEEN SOME DISAGREEMENT
IN THE MODEL GUIDANCE ON WHETHER STRATUS WILL COMPLETELY SCATTER OUT
TODAY. CURRENTLY ON SATELLITE, THERE IS SOME DRY AIR MAKING ITS WAY
TO OUR COAST. THIS DRY AIR COMBINED WITH A MODERATE ONSHORE FLOW
MAY BE ENOUGH TO SCATTER OUT THE REMAINING CLOUDS IN THE SF BAY.
MVFR CEILINGS RETURN AS WINDS EASE TO GENTLE AND PERSIST INTO
TUESDAY AFTERNOON. MEDIUM CONFIDENCE ON THE OVERALL FORECAST.
SFO BRIDGE APPROACH...STRATUS IS LIKELY TO BECOME PATCHY OVER THE
BRIDGE BEFORE SCATTERING OUT AT THE TERMINALS THIS
MORNING/EARLY AFTERNOON. OTHERWISE, SIMILAR TO SFO.
MONTEREY BAY TERMINALS...NORTHWEST TO WESTERLY BREEZES INCREASE TO
MODERATE THIS AFTERNOON AS MVFR CEILINGS SCATTER OUT. THE MARINE
LAYER IS LESS LIKELY TO MIX OUT DUE TO THE UPPER LEVEL TROUGH,
THEREFORE ANTICIPATE AN EARLY RETURN OF MVFR CEILINGS RIGHT
AROUND SUNSET.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 1156 AM PDT MON AUG 31 2026
NORTHWEST TO WESTERLY GENTLE BREEZES PREVAIL THROUGH THE WEEK AND
MAY BECOME MODERATE AT TIMES. WIND DRIVEN SEAS REMAIN SLIGHT TO
MODERATE THROUGH THE WEEK AS A LONG PERIOD SOUTHERLY SWELL
CONTINUES TO DIMINISH BY TUESDAY.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT TUESDAY FOR SF BAY N OF BAY
BRIDGE.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR MRY BAY.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...NAVARRETE
MARINE...NAVARRETE
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