839
FXHW60 PHFO 020131
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 PM HST SUN NOV 1 2009
SYNOPSIS
A COLD FRONT WILL BE MOVING ACROSS THE STATE EARLY THIS WEEK
BRINGING SHOWERS AND A CHANCE OF THUNDERSTORMS. DRIER AIR...COOLER
TEMPERATURES AND BREEZY NORTHEAST WINDS WILL FOLLOW IMMEDIATELY
BEHIND THE FRONT. WINDS AND WEATHER WILL GRADUALLY TREND BACK TO A
MORE SEASONAL TRADE WIND PATTERN FRIDAY INTO THE WEEKEND.
DISCUSSION
THERE HAVE NOT BEEN ANY BIG CHANGES IN THE FORECAST REASONING FROM
EARLIER IN THE SHIFT. SATELLITE DERIVED PRECIPITABLE WATER IMAGERY
DEPICTS RELATIVELY DRY AIR BEING ADVECTED OVER THE STATE IN THE
TRADE WINDS. COMBINED WITH A SUBSIDENCE/TRADE WIND INVERSION BETWEEN
6-7 KFT ONLY LIGHT SCATTERED SHOWERS ARE EXPECTED ALONG WINDWARD AND
MOUNTAIN TERRAIN OVERNIGHT. SATELLITE IMAGERY ALSO SHOWS AN AXIS OF
HIGHER PRECIPITABLE WATER VALUES NEARLY STATIONARY JUST NORTHWEST OF
THE KAUAI WHICH WILL WORK ITS WAY SOUTHEASTWARD LATER TONIGHT AS IT
INTERACTS WITH ANOTHER PASSING SHORTWAVE TROUGH. PWAT VALUES AROUND
KAUAI WILL BEGIN TO RISE SIGNIFICANTLY AFTER MIDNIGHT ALONG WITH
BACKING WINDS TO THE NORTHEAST AS THE REMNANT FRONTAL MOISTURE TO
THE NORTHWEST IS REINFORCED AND BEGINS MOVING SOUTHEASTWARD AGAIN AS
A COLD FRONT. THE FRONT WILL MOVE ACROSS THE STATE DURING THE FIRST
HALF OF THE WEEK BRINGING WIDESPREAD RAINFALL AND THE POSSIBILITY OF
THUNDERSTORMS TO KAUAI/OAHU/MAUI COUNTIES MAINLY MONDAY AND TUESDAY.
ANOTHER POTENT SHORTWAVE TROUGH CAN BE SEEN DIVING OUT OF THE BERING
SEA RIGHT NOW. THIS WILL INTENSIFY FURTHER AS IT PROGRESSES
SOUTHEAST PROVIDING ADDITIONAL COLD AIR ADVECTION TO PUSH THE FRONT
TO THE BIG ISLAND LATE TUESDAY NIGHT/EARLY WEDNESDAY MORNING WHERE
IT WILL SLOWLY WASH-OUT. CONDITIONS BEHIND THE FRONT WILL SEEM
NOTICEABLY COOLER AND WINDIER AS DRIER MID-LATITUDE AIRMASS MOVES
OVER THE STATE. THE CURRENT FORECAST DOES LOOK ON TRACK FOR THE
FRONTAL PASSAGE.
THE AFOREMENTIONED 500 MB SHORTWAVE DIVING OUT OF THE BERING SEA IS
EXPECTED TO CUT-OFF AND BECOME NEARLY STATIONARY NORTHEAST OF THE
STATE AS IT OCCLUDES. THE GFS/GFS ENSEMBLES AND ECMWF SOLUTIONS
REMAIN IN FAIRLY GOOD AGREEMENT REGARDING THE OVERALL TRAJECTORY...
PROPAGATION...AND PASSING OF SHALLOW FRONTAL BANDS IN THE
NORTHEASTERLY FLOW WHICH SHOULD CONTINUE INTO AT LEAST THURSDAY.
TRADES WILL RETURN TO A MORE SEASONAL ROUTINE FRIDAY INTO THE
WEEKEND...MAYBE AS EARLY AS LATE THURSDAY.
PREVIOUS DISCUSSION
/ISSUED 1000 AM HST SUNDAY/
WATER VAPOR IMAGERY SHOWS A WEAKENING SHORTWAVE TROUGH 350 MILES
WEST NORTHWEST OF KAUAI...AND A STRONGER DEVELOPING SHORTWAVE 800
MILES NORTHWEST OF KAUAI. ACROSS THE FAR NORTHERN PACIFIC...ALONG
170W JUST SOUTH OF 50N...THERE IS ANOTHER SYSTEM THAT MAY HAVE AN
IMPACT ON THE STATE DURING THE SECOND HALF OF THE WEEK. VISIBLE AND
IR IMAGERY SHOWS A RAGGED BAND OF CLOUDS NORTHWEST OF KAUAI
ASSOCIATED WITH A WEAKENING STATIONARY FRONT...WITH MORE TYPICAL
TRADE CONDITIONS ACROSS THE STATE. 12Z SOUNDINGS FROM LIHUE AND HILO
SHOW INVERSIONS RUNNING 6-7KFT...WITH PRECIPITABLE WATERS RANGING
FROM 1.1 AT LIHUE TO 1.4 AT HILO. THE AMSU/SSMI BLENDED TOTAL
PRECIPITABLE WATER IMAGERY IS SIMILAR ACROSS THE STATE...WITH PW
VALUES INCREASING TO 1.6-1.8 INCHES IN A BAND ALONG THE OLD FRONT.
AS THE FARTHER NORTHWEST SYSTEM DIGS TOWARD THE STATE...IT WILL PICK
UP THE WEAKER SYSTEM HELP TO REINVIGORATE THE SURFACE FRONT. THE 12Z
GFS IS A BIT WEAKER AND SLOWER THAN EARLIER RUNS...BUT SHOWS THE
BOUNDARY REACHING KAUAI MONDAY NIGHT AND PROGRESSING DOWN THE ISLAND
CHAIN THROUGH TUESDAY NIGHT. WHILE THIS FEATURE LOOKS MORE LIKE A
SHEARLINE...WITH EASTERLY WINDS PRECEDING IT AND STRONGER
NORTHEASTERLY WINDS FOLLOWING IT...THERE IS A CHANGE IN AIRMASS
WITH 850MB TEMPERATURES DROPPING 2-3C BEHIND IT. WINDS WILL ALSO BE
STRONGER BEHIND THE BOUNDARY AS THE COOLER AIR MOVING ACROSS WARMER
WATER LEADS TO MORE UNSTABLE CONDITIONS AND GREATER MIXING WITHIN
THE BOUNDARY LAYER. THE HIGHER RESOLUTION NAM AND RSM SEEM TO HAVE A
BETTER HANDLE ON THE WINDS THAN THE GFS.
BY MIDWEEK...ATTENTION TURNS TO A DEVELOPING SYSTEM EAST OF THE
STATE. THE SHORTWAVE CURRENTLY NEAR 50N MENTIONED ABOVE WILL DIG
SOUTHEASTWARD AND EVENTUALLY CUTOFF. THIS IS THE SYSTEM THAT THE
EXTENDED MODELS HAVE BEEN HAVING TROUBLE WITH THE PAST FEW DAYS. THE
12Z GFS HAS CONTINUED THE TREND OF ITS RECENT RUNS...DEVELOPING THE
LOW FARTHER EAST AWAY FROM THE STATE. THE 12Z ENSEMBLES STILL SHOW
10-15 DEGREES OF SPREAD LONGITUDINALLY AS TO WHERE THE LOW WILL
DEVELOP...WHICH IS BETTER THAN THE 30-40 DEGREES OF SPREAD FROM
EARLIER RUNS. THE ENSEMBLES BREAK DOWN INTO TWO MAIN GROUPS...A MORE
CUTOFF/MORE WESTERLY ONE WHICH INCLUDES THE OPERATIONAL RUN AND A
MORE PROGRESSIVE/MORE EASTERLY ONE. EITHER WAY...IT PLACES HAWAII
MORE SOLIDLY IS A PERSISTENT NORTHEASTERLY FLOW THAN EARLIER RUNS.
THE 12Z ECMWF ALSO SHOWS THE SAME TREND...DEVELOPING THE CUTOFF LOW
FARTHER EAST AND KEEPING US UNDER STRONGER NORTHEASTERLIES. GIVEN
THE CONSISTENT TREND OF THE EXTENDED MODELS...WITH ADJUST THE
FORECAST TOWARD THIS SOLUTION.
MARINE
LARGE HEAVY SURF CONTINUES TO POUND NORTH FACING SHORES THIS
AFTERNOON. BUOY DATA AND OBSERVATIONS STILL SUPPORT THE CURRENT HIGH
SURF ADVISORY. SURF IS STILL WELL ABOVE THE ADVISORY LEVEL OF 15
FEET. SURF WILL CONTINUE TO REACH UP TO 20 FEET THROUGH THE
REMAINDER OF THE DAYLIGHT HOURS TODAY AS A SLOW DOWNWARD TREND
BEGINS OVERNIGHT. THE ADVISORY STILL EXPIRES MONDAY EVENING AT 6 PM
HST...EXCEPT HAVE TRIMMED THE EXPIRATION TIME FOR WEST FACING OAHU
BACK TO 6 AM HST MONDAY MORNING. IN ADDITION...WITH THE HIGHER SWELL
AND HIGHER SIGNIFICANT WAVE HEIGHTS...WE HAVE ISSUED A SMALL CRAFT
ADVISORY FOR 10 FOOT SEAS FOR THE NORTHWEST COASTAL WATERS THROUGH
TONIGHT.
WINDS WILL INCREASE TO SMALL CRAFT ADVISORY LEVELS OF 25 KNOTS
BEHIND THE COLD FRONT. WINDS WILL BE STRONGEST AGAIN ACROSS
NORTHWEST WATERS...WHERE THE FRONT WILL HAVE THE MOST STRENGTH. THE
MORNING QUIKSCAT PASS SHOWED WINDS OF 25 KNOTS BEHIND THE
BOUNDARY...AND 12Z NAM/RSM SHOW WINDS OF THIS STRENGTH REACHING
KAUAI LATE MONDAY.
AVIATION
VFR CONTINUES FOR THE TERMINALS THIS AFTERNOON. ONLY ISOLATED LIGHT
SHRA IS AFFECTING WINDWARD TERRAIN. ANY MVFR CIGS/VIS ARE MINIMAL
AND SHORT LIVED RIGHT NOW. CHANCES FOR MORE WIDESPREAD FLIGHT
RESTRICTIONS WILL COME LATER TONIGHT AND INTO MONDAY AS A FRONT
APPROACHES FROM THE NORTHWEST. EXPECTING STRONGER NORTHEAST WINDS
BEHIND THE FRONT AS WELL CAPABLE OF PRODUCING GUSTS OVER 30 KT
PRODUCING SIGNIFICANT LOW LEVEL TURB. AS THE FRONT PASSES...MOUNTAIN
OBSCURATION MAY ALSO BECOME AN ISSUE.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 6 PM HST MONDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-WINDWARD
HALEAKALA.
SMALL CRAFT ADVISORY UNTIL 10 PM HST THIS EVENING FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL-OAHU WINDWARD WATERS.
PUBLIC/AVIATION...DEJESUS
MARINE...DEJESUS/BRAVENDER
PREVIOUS...BRAVENDER
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