236
FXHW60 PHFO 022013
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST MON NOV 2 2009
SYNOPSIS
MODERATE TRADE WINDS WILL BRING SHOWERS TO WINDWARD AND MAUKA AREAS
THROUGH TONIGHT...BEFORE A COLD FRONT USHERS IN A WEATHER CHANGE
TUESDAY AND TUESDAY NIGHT. THE FRONT WILL BRING ADDITIONAL SHOWERS
TO MOST ISLANDS...AND A SLIGHT CHANCE OF THUNDERSTORMS TO KAUAI...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 400 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. 12Z SOUNDINGS FROM HILO AND LIHUE SHOW INVERSIONS NEAR 7KFT
AND PRECIPITABLE WATERS FROM 1.2 TO 1.4 INCHES RESPECTIVELY. THE
AMSU/SSMI BLENDED TOTAL PRECIPITABLE WATER IMAGERY SHOWS SIMILAR
VALUES NEAR THE STATE...WITH PW VALUES OF 1.6-1.8 INCHES POOLED
ALONG THE BOUNDARY TO THE NORTHWEST.
THE 12Z MODELS ARE IN SIMILAR AGREEMENT WITH THE TIMING OF THE
BOUNDARY ACROSS THE STATE...AND HAVE ALL TRENDED SLOWER WITH ITS
APPROACH. HAVE ADJUSTED THE WIND FORECAST TO ACCOUNT FOR THE SLOWER
MOVEMENT...AND WILL MAKE SIMILAR ADJUSTMENTS TO THE POP AND WEATHER
FIELDS AS WELL. THUNDER POTENTIAL ALONG THE BOUNDARY LOOKS MARGINAL.
THERE IS SUFFICIENT MOISTURE...BUT MID-LEVEL TEMPERATURES ARE NOT AS
COLD AS EARLIER PROJECTIONS. 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 12Z NAM/RSM CONTINUE TO SHOW WIND VALUES OF +25KT OVER THE
COASTAL WATERS FOLLOWING THE FRONT. THESE VALUES SEEM REASONABLE
GIVEN THE INITIALIZATION COMPARED TO UPSTREAM QUIKSCAT VALUES BEHIND
THE FRONT. WINDS WILL 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. WINDS WILL DIMINISH RATHER
QUICKLY WEDNESDAY/WEDNESDAY AS THE STRONG HIGH NORTHWEST OF THE
STATE WEAKENS...CAUSING THE GRADIENT BEHIND THE FRONT TO DIMINISH. A
SURGE OF DRIER AIR WILL ALSO SPREAD ACROSS THE STATE
WEDNESDAY/WEDNESDAY NIGHT.
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 WAIMEA BUOY SHOWS THE CURRENT NORTHWEST SWELL CONTINUES TO
DIMINISH. THE 12Z WAVEWATCH III GUIDANCE IS PRETTY WELL IN LINE WITH
THE BUOY READINGS. NO CHANGES ARE EXPECTED TO THE HIGH SURF
ADVISORY...WHICH REMAINS IN EFFECT THROUGH THE AFTERNOON.
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. THE SMALL CRAFT ADVISORY
WILL LIKELY NEED TO BE EXPANDED WITH THE AFTERNOON PACKAGE TO COVER
THESE AREAS FOR TUESDAY.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 6 PM HST TODAY FOR NIIHAU-KAUAI WINDWARD-
KAUAI LEEWARD-OAHU NORTH SHORE-OAHU KOOLAU-MOLOKAI-MAUI WINDWARD
WEST-MAUI CENTRAL VALLEY-WINDWARD HALEAKALA.
BRAVENDER
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