553
FXUS66 KEKA 071023
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
323 AM PDT MON SEP 7 2026
KEY MESSAGES
* CONVECTIVE POTENTIAL REMAINS LOW (UP TO 15% CHANCE) AND LIMITED
TO NORTHERN TRINITY AND FAR INTERIOR DEL NORTE THROUGH EARLY
EVENING.
* EXPANDING HIGH PRESSURE ALOFT AND COMPRESSING MARINE AIR WILL
DRIVE A SHARP WARMING TREND TUESDAY THROUGH THURSDAY, BRINGING
INCREASED HEATRISK POTENTIAL AND TEMPERATURES 10-15 DEGREES ABOVE
EARLY SEPTEMBER NORMALS ACROSS INTERIOR VALLEYS.
SYNOPSIS
A MID-LEVEL DISTURBANCE EXITS THE REGION. ATMOSPHERIC
HIGH PRESSURE CENTERED OVER THE DESERT SOUTHWEST WILL BUILD
WESTWARD STARTING MONDAY, INITIATING A PRONOUNCED WARMING TREND
THROUGH MID-WEEK. OFFSHORE FLOW ON WEDNESDAY WILL CLEAR COASTAL
LOW CLOUDS TEMPORARILY BEFORE MARINE AIR MODERATES CONDITIONS LATE
IN THE WEEK.
DISCUSSION
A TROUGH EXITS THE REGION WITH MID LEVEL HEIGHTS
QUICKLY INCREASING ACROSS THE REGION FROM A STRONG DESERT
SOUTHWEST AREA OF HIGH PRESSURE. THE RIDGE EXPANDS NW THROUGH
MIDWEEK, WITH 500 HEIGHTS RISING TO 591 TO 594 DAM. AN ANOMALOUSLY
WARM AIRMASS WILL ACCOMPANY THE RIDGE, WITH 850 MB TEMPERATURES
INCREASING TO 24 TO 26C. DEEP DAYTIME MIXING OF THIS WARM AIRMASS
SUPPORTS WIDESPREAD UPPER 90S TO LOWER 100S ACROSS N CA INTERIOR.
ADDITIONALLY, A DEVELOPING THERMAL TROUGH AND OFFSHORE COMPONENT
TO THE LOW LEVEL FLOW SHOULD LIMIT MARINE INFLUENCE AND ENHANCE
WARMING, ESPECIALLY WEDNESDAY.
THE HOT CONDITIONS WILL REACH THE COAST, WITH A HIGH PROBABILITY
OF TEMPERATURES REACHING THE 70, AND PERHAPS UPPER 70S TO EVEN LOW
80S IF THE OFFSHORE WINDS ARE FULLY REALIZED. INTERIOR VALLEYS
SUCH AS GARBERVILLE AND UKIAH HAVE OVER A 70 PERCENT CHANCE OF
EXCEEDING 100 WEDNESDAY, AND 850 TEMPERATURES SUPPORT THESE
VALUES. THERE IS ALSO A LESSER 34 TO 45 PERCENT CHANCE OF A
MAXIMUM HIGH TEMPERATURE OF 105 IN THE DESCRIBED LOCATIONS,
INCLUDING THE HOOPA THROUGH WILLOW CREEK VALLEYS. IF THIS HIGH
VALUE OCCURS, IT SHOULD BE VERY LOCALIZED. THIS HEAT IN
COMBINATION WITH WARM OVERNIGHT LOWS IN THE 60S WILL YIELD
MODERATE HEATRISK (2/4), WITH LOCALIZED MAJOR (3/4) CATEGORY
POSSIBLE.
WHILE TEMPERATURES MAY REMAIN BELOW ADVISORY CRITERIA, SOME
CAUTION IS WARRANTED FOR THOSE SPENDING EXTENDED PERIODS OUTDOORS.
THE RAPID TRANSITION FROM THE RECENT COOL AND TROUGHY PATTER WILL
PROVIDE LITTLE OPPORTUNITY TO ACCLIMATE TO THE QUICKLY BUILDING
HEAT. THIS MAY BE PARTICULARLY NOTICEABLE IN NORMALLY COOLER
COASTAL AND NEAR-COASTAL AREAS, WHERE TEMPERATURES COULD REACH
LEVELS NOT EXPERIENCED SO FAR THIS SEASON.
A COMPLICATION TO THE HIGH TEMPERATURE FORECAST WILL DEVELOP AS A
SLUG OF TROPICAL MOISTURE MOVES THROUGH THE REGION WEDNESDAY OFF
PASSING TROPICAL SYSTEM MARIE. MODELS AND NBM PROBABILITIES SHOW
VERY LITTLE TO NO INSTABILITY COINCIDING WITH THE MOISTURE, AND
THE ENVIRONMENT WILL BE STRONGLY CAPPED. THIS WILL LIMIT
THUNDERSTORM CHANCES TO LESS THAN 5 PERCENT, BUT ASSOCIATED CLOUD
COVER COULD SUPPRESS THE HIGH TEMPERATURE POTENTIAL OF THE
THICKNESS IS SUFFICIENT. HIGH TEMPERATURES WILL QUICKLY LOWER
AGAIN FRIDAY AND THROUGH THE WEEKEND AS TROUGHING RETURNS.
AVIATION
MARINE LOW CLOUDS WILL RETURN ALONG THE COAST AFTER
07Z, WITH A DECREASED PROBABILITY OF 40% FOR LIFR CONDITIONS INTO
MONDAY MORNING FOR MAINLY AROUND HUMBOLDT BAY AND UP THE EEL
RIVER DELTA. WHAT DOES FORM WILL QUICKLY DISSIPATE MONDAY MORNING.
LIGHT OFFSHORE FLOW AND DRYING CONDITIONS WILL MAINTAIN VFR
ELSEWHERE. REGIONAL TERMINAL KUKI WILL REMAIN VFR THROUGHOUT THE
PERIOD WITH LIGHT DAYTIME WEST NORTHWEST WINDS MONDAY AFTERNOON.
MARINE
AN OFFSHORE HIGH-PRESSURE SYSTEM INTERACTING WITH THE
COASTAL THERMAL LOW CONTINUES TO DRIVE NORTHERLY WINDS, STRONGEST
ACROSS THE SOUTHERN MARINE ZONES.
FOR THE NORTHERN INNER WATERS, NORTH WINDS OF 10 TO 15 KNOTS WITH
GUSTS TO 20 KNOTS WILL PERSIST THROUGH MONDAY. COMBINED SEAS WILL
AVERAGE 4 TO 6 FEET, COMPOSED OF A DOMINANT NORTHWEST WIND WAVE OF 4
FEET AT 8 SECONDS AND A LONG-PERIOD SOUTHERLY SWELL OF 2 TO 3 FEET
AT 15 SECONDS.
FOR THE NORTHERN OUTER WATERS, NORTHERLY WINDS WILL RANGE FROM 15 TO
20 KNOTS. WAVE STEEPNESS REMAINS MARGINAL WITH DOMINANT PERIODS
AROUND 9 SECONDS. THIS DECISION IS DEFERRED TO THE UPCOMING MIDNIGHT
SHIFT AS SEA STATE CRITERIA REMAIN MARGINAL.
FOR THE SOUTHERN INNER WATERS, A SMALL CRAFT ADVISORY REMAINS ACTIVE
THROUGH 5 AM MONDAY FOR NORTH-NORTHWEST WINDS OF 15 TO 25 KNOTS AND
WAVE HEIGHTS OF 6 TO 8 FEET AT 8 SECONDS.
FOR THE SOUTHERN OUTER WATERS, A SMALL CRAFT ADVISORY CONTINUES
THROUGH 5 PM MONDAY FOR NORTH WINDS OF 20 TO 25 KNOTS, GUSTS TO 30
KNOTS, AND STEEP SEAS OF 7 TO 9 FEET AT 9 SECONDS.
ADDITIONALLY, A SOUTH-SOUTHWEST SWELL OF 3 TO 5 FEET AT 15-16
SECONDS FROM HURRICANE MARIE WILL DECAY ACROSS ALL WATERS THROUGH
MONDAY NIGHT. A THERMAL TROUGH POSITIONING OVER THE COASTLINE
WEDNESDAY WILL BRIEFLY REDUCE WIND SPEEDS ACROSS ALL WATERS BEFORE
NORTHERLY FLOW RE-STRENGTHENS THURSDAY EVENING.
FIRE WEATHER
HIGH PRESSURE BUILDING OVER THE REGION MONDAY THROUGH
MID-WEEK WILL BRING MUCH WARMER AND DRIER CONDITIONS. HIGH
TEMPERATURES IN INTERIOR VALLEYS WILL CLIMB INTO THE 98 TO 102
DEGREE RANGE TUESDAY THROUGH THURSDAY, WITH AFTERNOON HUMIDITY
LEVELS DROPPING BETWEEN 12 AND 22 PERCENT. WINDS WILL FOLLOW
STANDARD DAILY PATTERNS, BLOWING UPHILL DURING THE DAY AND DOWN THE
VALLEYS AT NIGHT. BRIEF OFFSHORE WINDS WEDNESDAY MORNING WILL SPREAD
WARM TEMPERATURES AND LOWER HUMIDITY CLOSER TO THE COAST BEFORE FOG
AND LOW CLOUDS REBUILD LATE IN THE WEEK. OFFSHORE WINDS MAY BE
LOCALLY BREEZY AND WILL NEED TO BE MONITORED GIVEN THE EXPECTED
HEAT AND LOW RH.
BEACH HAZARDS
A LONG PERIOD SOUTHERLY CONTINUES IN WATERS, ONLY
SLOWLY LOSING ENERGY THROUGH THE WEEK, BUT 15 TO 16 SECOND PERIODS
ARE STILL BEING RECORDED. THUS, THERE IS AN ONGOING RISK OF
SNEAKER WAVES MONDAY FOR SOUTH FACING BEACHES IN MENDOCINO AND
SOUTHERN HUMBOLDT COUNTIES, INCLUDING THE LOST COAST TRAIL.
SNEAKER WAVES ARE A UNIQUE HAZARD, WITH UP TO 30 MINUTES BETWEEN
WAVES. LARGE, UNEXPECTED WAVES CAN SWEEP ACROSS THE BEACH WITHOUT
WARNING, SWEEPING PEOPLE INTO THE SEA FROM ROCKS, JETTIES, AND
BEACHES. THESE SNEAKER WAVES CAN ALSO MOVE LARGE OBJECTS SUCH AS
LOGS, CRUSHING ANYONE CAUGHT UNDERNEATH. EVEN ANKLE TO KNEE DEEP
WATER CAN KNOCK YOU DOWN AND DRAG YOU OUT WHEN A SNEAKER WAVE HITS.
PAY ATTENTION AND STAY ABOVE THE HIGH WATER LINE AND ANY WET SAND TO
STAY SAFE. IF THE GROUND IS WET, WAVES HAVE SURGED THERE RECENTLY.
STAY SAFE AND NEVER TURN YOUR BACK ON THE OCEAN!
EKA WATCHES/WARNINGS/ADVISORIES
CA...
BEACH HAZARDS STATEMENT THROUGH MONDAY EVENING FOR CAZ104-
109.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 5 AM PDT MONDAY FOR PZZ455.
SMALL CRAFT ADVISORY UNTIL 5 PM PDT MONDAY FOR PZZ475.
NOTE: THE FULL FORECAST DISCUSSION IS NOW REGULARLY ISSUED BETWEEN
10 AM/PM AND 1 PM/AM. ADDITIONAL UPDATES WILL BE ISSUED AS NEEDED.
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