986
FXHW60 PHFO 030139
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST MON NOV 2 2009
SYNOPSIS
MODERATE TRADE WINDS WILL BRING SHOWERS TO WINDWARD AND MAUKA AREAS
TONIGHT...BEFORE A COLD FRONT USHERS IN A WEATHER CHANGE TUESDAY AND
TUESDAY NIGHT. THE FRONT WILL BRING ADDITIONAL SHOWERS TO MOST
ISLANDS AS IT MOVES DOWN THE ISLAND CHAIN. STRONG NORTHEAST WINDS
WILL FOLLOW IMMEDIATELY BEHIND THE FRONT...AND WILL BRING IN A
COOLER AIR MASS THAT WILL LINGER FOR A COUPLE OF DAYS. A RETURN TO
TRADE WIND WEATHER IS EXPECTED FOR THE SECOND HALF OF THE WEEK.
DISCUSSION
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL RIDGE OVER THE STATE...WITH
A DIGGING TROUGH ABOUT 350 MILES NORTHWEST OF KAUAI. THIS TROUGH IS
HELPING TO REINVIGORATE A STALLED SURFACE FRONT NORTHWEST OF THE
STATE...AND WILL PROPEL IT SOUTHEASTWARD ACROSS US TUESDAY/TUESDAY
NIGHT. HOWEVER...OVER THE PAST 12 HOURS THE LEADING EDGE OF THE
FRONTAL CLOUD BAND HAS MOVED VERY LITTLE. 00Z SOUNDINGS FROM HILO
AND LIHUE SHOW INVERSIONS NEAR 7-8KFT AND PRECIPITABLE WATERS OF
1.3-1.4 INCHES. THE AMSU/SSMI BLENDED TOTAL PRECIPITABLE WATER
IMAGERY SHOWS SIMILAR VALUES NEAR THE STATE...WITH PW VALUES UP TO
1.8 INCHES POOLED ALONG THE BOUNDARY TO THE NORTHWEST.
IN THE NEAR TERM THIS EVENING...WIDESPREAD CLOUDS AND SHOWERS WILL
CONTINUE TO AFFECT OAHU AND MOLOKAI THIS EVENING. A LOW-LEVEL SWIRL
CAN BE SEEN ON VISIBLE IMAGERY NORTH OF MAUI COUNTY...WHICH IS
HELPING TO MAINTAIN THIS AREA OF CLOUDS. THE SWIRL HAS BEEN MOVING
SLOWLY WESTWARD. HOWEVER...AT SOME POINT IT WILL SLOW AND STALL AS
THE IT BECOMES BLOCKED BY THE FRONT. THE 18Z GFS LATCHES ONTO THIS
FEATURE MORE THAN EARLIER RUNS...AND MAKES IT THE PRIMARY WEATHER
PRODUCER FOR THE CENTRAL ISLANDS. HAVE INCREASED POPS/CLOUDS/WEATHER
FOR OAHU THIS EVENING...AND ALSO NUDGED THEM UP OVERNIGHT.
THE 18Z MODELS HAVE CONTINUED THE TREND OF THE EARLIER RUNS...AND
ARE SLOWER YET TO BRING THE FRONT ACROSS THE STATE. HAVE ADJUSTED
THE WIND AND POP/WEATHER/SKY GRIDS TO REFLECT THE SLOWER MOVEMENT.
THUNDER POTENTIAL CONTINUES TO LOOK MARGINAL. HOWEVER...AMSU/SSMI
IMAGERY SHOWS ADDITIONAL MOISTURE CONTINUES TO POOL ALONG THE
FRONT...WITH VALUES ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL FOR US.
DURING THE DAY THERE HAVE BEEN A COUPLE STRONGER UPDRAFTS THAT
DEVELOPED ALONG THE FRONTAL BAND...BUT NOTHING VERY PERSISTENT. BY
THE TIME THE FRONT REACHES THE MAIN HAWAIIAN ISLANDS...THE MAIN
UPPER LEVEL SUPPORT AND MID-LEVEL COLD POOL WILL HAVE SHIFTED
EASTWARD. WILL TRIM BACK THE THUNDER MENTION TO JUST KAUAI AND
ADJACENT WATERS...WHERE THERE IS THE GREATER OVERLAP OF MOISTURE AND
INSTABILITY.
THE MORNING QUIKSCAT PASS SHOWED 25-30 KNOTS OF WIND OVER THE OPEN
OCEAN BEHIND THE FRONT...AND BUOYS 51001 AND 51101 BOTH HAVE BEEN
REPORTING WINDS OF 30 KNOTS GUSTING INTO THE MID 30S. WILL KEEP THE
FORECAST GEARED TOWARD THE STRONGER NAM/RSM. THE GFS IS TOO WEAK
GIVEN THE STRENGTH OF THE CURRENT PRESSURE GRADIENT AND THE UNSTABLE
BOUNDARY LAYER UNDER COLD ADVECTION BEHIND THE FRONT. THE HIGH
NORTHWEST OF THE STATE...RESPONSIBLE FOR THE STRONG GRADIENT AND
WINDS BEHIND THE FRONT...IS NEAR ITS PEAK STRENGTH AND IS EXPECTED
TO WEAKEN OVER THE NEXT COUPLE DAYS. GIVEN THIS WEAKENING TREND...AM
HESITANT ABOUT GOING TOO STRONG WITH WINDS ACROSS THE ISLANDS. GIVEN
THE CURRENT STRENGTH OF THE HIGH...WE WOULD PROBABLY REACH WIND
ADVISORY LEVELS OF 30 MPH ACROSS THE ISLANDS. HOWEVER...WITH THE
HIGH EXPECTED TO WEAKEN...WINDS SHOULD REMAIN BELOW THAT THRESHOLD.
WILL CARRY WINDS OF UP TO 20 TO 25 MPH FOR TUESDAY INTO TUESDAY
NIGHT. A SURGE OF DRIER AIR WILL ALSO SPREAD ACROSS THE STATE
WEDNESDAY/WEDNESDAY NIGHT BEHIND THE FRONT.
FOR THURSDAY THROUGH THE WEEKEND...THE ECMWF/GFS CONTINUE TO TREND
MORE PROGRESSIVE WITH A SYSTEM THAT NOW IS EXPECTED TO DEVELOP WELL
EAST OF THE STATE. AN UPPER LEVEL RIDGE WILL DOMINATE OVER THE
ISLANDS...BETWEEN LOWS THAT DEVELOP TO THE EAST AND TO THE WEST. THE
PAST COUPLE RUNS OF THE GFS HAVE SHOWN A SECONDARY COLD FRONT OR
TRADE WIND SURGE REACHING US THURSDAY/FRIDAY...HELPING TO ENHANCE
WINDWARD AND MAUKA SHOWERS. HIGH PRESSURE WILL ALSO MOVE NORTHEAST
OF THE STATE...ALLOWING WINDS TO RETURN TO A MORE EASTERLY TRADE
DIRECTION /AS OPPOSED TO THE NORTHEAST WINDS MID-WEEK/. THE GFS AND
ECMWF SHOW THE LOW WEST OF THE STATE LIFTING NORTHEASTWARD THIS
WEEKEND...WHICH MAY WEAKEN AND DISPLACE THE RIDGE SOUTHWARD OVER US.
HOWEVER...AT THIS POINT IT DOES NOT LOOK AS THOUGH THIS SYSTEM WILL
HAVE A DIRECT IMPACT ON US.
MARINE
THE CURRENT NORTHWEST SWELL HAS CONTINUE TO DIMINISH. THE WAIMEA
BUOY HAS DROPPED TO 6 FEET/12 SECONDS...AND SURF REPORTS INDICATE
THAT SURF HEIGHTS HAVE DROPPED BELOW ADVISORY LEVELS. THEREFORE WE
WILL DROP THE HIGH SURF ADVISORY WITH THIS PACKAGE.
A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE TYPICALLY WINDIER
LOCATIONS NEAR THE BIG ISLAND. GIVEN THE SLOWER APPROACH OF THE
FRONT...HAVE DELAYED THE INCREASE IN WIND SPEEDS ACROSS THE
NORTHWEST COASTAL WATERS UNTIL TUESDAY/TUESDAY NIGHT. HOWEVER...A
SOLID 25 KNOTS OF WINDS ARE EXPECTED WITH THE FRONT. HAVE EXPANDED
THE SMALL CRAFT TO INCLUDE WATERS NEAR KAUAI BEGINNING ON TUESDAY.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.
SMALL CRAFT ADVISORY FROM 6 AM TUESDAY TO 6 AM HST WEDNESDAY FOR
KAUAI NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD
WATERS-KAUAI CHANNEL.
BRAVENDER
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