646
FXUS66 KMTR 041806
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1106 AM PDT FRI SEP 4 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1151 PM PDT THU SEP 3 2026
- COASTAL FLOOD ADVISORY IN EFFECT AROUND HIGH TIDE BAYSIDE
MARIN COUNTY FRIDAY AFTERNOON AND EVENING
- HAZARDOUS BEACH CONDITIONS AT PACIFIC COAST BEACHES FRIDAY
THROUGH MONDAY
- BELOW NORMAL TEMPERATURES THROUGH THE WEEKEND, A GRADUAL
WARMING AND DRYING TREND MONDAY THROUGH WEDNESDAY
SHORT TERM
ISSUED AT 103 AM PDT FRI SEP 4 2026
(TODAY AND TONIGHT)
A 500 MB LOW PRESSURE SYSTEM (GEOPOTENTIAL HEIGHT 555 DECAMETERS,
MUCH BELOW NORMAL FOR EARLY SEPTEMBER) WILL MOVE ONSHORE OVER OREGON
TODAY. OVER OUR FORECAST AREA 500 MB HEIGHTS ARE IN THE 570 DECAMETERS
RANGE WHICH IS NEAR THE 10TH PERCENTILE FOR EARLY SEPTEMBER. IF IT
WAS ANY TIME IN THE COOL SEASON 570S WOULD NOT BE A BIG DEAL OR
IMPRESSIVE. HOWEVER, FOR EARLY SEPTEMBER MUCH BELOW NORMAL HEIGHTS
OVER OUR AREA ARE DUE TO CHILLY TEMPS IN THE AIR COLUMN ABOVE PER
INSPECTION OF THE 925 MB, 850 MB, 700 MB TEMPS ON THE OAKLAND AIR
UPPER SOUNDING. THESE READINGS ARE NEAR OR LESS THAN THE 10TH
PERCENTILE AS WELL, I.E. AT THE LOWER END (COOL TEMPS) BUT WITHIN
OAKLAND UPPER AIR LONG TERM CLIMATOLOGY FOR EARLY SEPTEMBER SINCE
1948. THE CURRENT WEATHER PATTERN IS A GREAT EXAMPLE OF WATER
VAPOR RICH AIR (PRECIPITABLE WATER WAS 1.35", NEAR THE EARLY SEP
MAX MOVING AVERAGE) AND COOL AIR WITHIN A TROUGH OF LOW PRESSURE
RESULTING IN AREAS OF MEASURABLE PRECIPITATION, IN EARLY SEPTEMBER
(NORMALLY THE THIRD DRIEST MONTH BEHIND JULY AND AUGUST) WHEN
IT'S TYPICALLY WARMER/HOT AND DRY WHEN E.G. SEP-OCT FAVOR OFFSHORE
WINDS. THE LARGER SCALE NORTHERN HEMISPHERIC PATTERN CONTINUES TO
BE ACTIVE WITH ~ 6 LONG WAVE TROUGHS, A SIGNATURE OF RATHER STRONG
JET STREAM WINDS, WIND SHEAR AND UNSTEADY FLOW. THE AUGUST PACIFIC
DECADAL OSCILLATION REMAINED NEGATIVE. THE NORTH PACIFIC HIGH AND
ITS CLOCKWISE WIND FLOW REMAINED RATHER ROBUST. A STRONG EQUATOR
TO POLE TEMPERATURE GRADIENT CONTINUES, AND NOT TO MENTION THREE
HURRICANES AT THE SAME TIME IN THE EASTERN PACIFIC, A POWERFUL
SHOW OF THERMODYNAMICS (FLOW OF HEAT) FROM SEA SURFACE TO THE
HIGHEST THUNDERSTORM CLOUD TOPS. JUST LIKE A CUP OF HOT COFFEE, AN
OPEN SYSTEM WHERE HEAT AND MASS ARE FREE TO FLOW, 100% WHENEVER
THERE IS AN IMBALANCE HEAT AND MASS WILL FLOW.
BACK TO OUR AREA, WITHIN THE AFOREMENTIONED LONG WAVE TROUGH A
MUCH SMALLER SCALE COOL FRONTAL BOUNDARY WITH AREAS OF LIGHT
MEASURABLE RAIN WILL CONTINUE TO MOVE SOUTHEASTWARD OVER THE
FORECAST AREA TODAY. EARLY SEPTEMBER RAINFALL HAS REACHED A FEW
RECORDS, WE PLAN TO SEND A RECORD EVENT REPORT ON THIS OVERNIGHT.
DRY WEATHER REVISITS THE AREA TODAY IN THE POST FRONTAL COOLER THAN
NORMAL AIR MASS FOR EARLY SEPTEMBER. FORECAST DAYTIME HIGHS WILL
VARY FROM THE 60S COASTSIDE/BAYSIDE TO THE 70S/80 INLAND.
LONG TERM
ISSUED AT 103 AM PDT FRI SEP 4 2026
(SATURDAY THROUGH NEXT THURSDAY)
JET STREAM WINDS AND ADDITIONAL SHORTWAVE ENERGY WILL GENERALLY
REACH THE BASE OF THE 500 MB LOW PRESSURE SYSTEM OVER THE WEST.
THIS WILL PROVIDE FORWARD MOTION TO THE LOW, NUDGING THE SOUTHERN
U.S. HIGH FORWARD THROUGH EARLY TO MID NEXT WEEK. THE REDEVELOPMENT
OF 500 MB TROUGHING OVER THE EASTERN PACIFIC DURING THE MIDDLE OF
NEXT WEEK WILL PROVIDE A SMALL CHANCE OF ENTRAINING TROPICAL MOISTURE.
THIS IS A LONG TIME FROM NOW, IT'S A LOW CONFIDENCE FORECAST, BUT
BEARS MONITORING.
AVIATION
(18Z TAFS)
ISSUED AT 1045 AM PDT FRI SEP 4 2026
VFR IS EXPECTED TO PERSIST THROUGH THE REMAINDER OF TODAY AND
TONIGHT FOR A MAJORITY OF THE TERMINALS. MONTEREY BAY SITES MAY
SEE A RETURN OF MVFR/IFR CEILINGS IN THE HOURS AFTER MIDNIGHT BUT
CONFIDENCE IS LOW IN THE EXTENT AND TIMING OF STRATUS
REDEVELOPMENT WHILE THE MARINE LAYER ATTEMPTS TO REORGANIZE THIS
WEEKEND IN THE WAKE OF THE WEAK COLD FRONT PASSING EAST TODAY.
VICINITY OF SFO...VFR IS EXPECTED TO PREVAIL WITH BREEZY DIURNAL
ONSHORE FLOW THAT WILL EASE AFTER SUNSET. THERE IS A CHANCE OF
MVFR CEILINGS AROUND SUNRISE, MORE LIKELY AT KOAK IF THEY DEVELOP,
OTHERWISE VFR.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR THROUGH THE REMAINDER OF TODAY AND
TONIGHT WITH LOW CONFIDENCE IN TIMING AND EXTENT OF MVFR/IFR
CEILING DEVELOPMENT AFTER MIDNIGHT INTO THE EARLY PRE-DAWN HOURS
SATURDAY.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 1045 AM PDT FRI SEP 4 2026
GENTLE TO MODERATE WEST/NORTHWEST BREEZES WILL PERSIST THROUGH
THE WEEKEND INTO NEXT WEEK, WHEN THEY BECOME MORE WIDESPREAD.
OCCASIONALLY STRONG GUSTS ARE POSSIBLE ACROSS THE SAN PABLO, SAN
FRANCISCO BAY AND MONTEREY BAYS. TROPICAL ACTIVITY WILL CONTINUE
TO PRODUCE LONG PERIOD SOUTHERLY SWELL THROUGH THE WEEKEND INTO
THE BEGINNING OF 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 THROUGH MONDAY EVENING FOR CAZ006-505-
509-529-530.
COASTAL FLOOD ADVISORY FROM 4 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR CAZ506.
PZ...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR MRY BAY.
SHORT TERM...CANEPA
LONG TERM....CANEPA
AVIATION...JM
MARINE...JM
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