FXHW60 PHFO 281949
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
950 AM HST SAT NOV 28 2009
.SYNOPSIS...
MODERATE TRADE WINDS AND WINDWARD SHOWERS BOTH WILL DIMINISH TODAY.
AN UPPER LEVEL DISTURBANCE IN MIDDLE ATMOSPHERE WILL SPREAD HEAVIER
SHOWERS AND A FEW THUNDERSTORMS ACROSS THE STATE SUNDAY AND MONDAY.
MORE TYPICAL TRADE WIND CONDITIONS WILL RETURN BY MID-WEEK FOLLOWED
BY LIGHT SOUTHEASTERLY WINDS AROUND THURSDAY. ANOTHER COLD FRONT
WILL APPROACH THE STATE NEXT WEEKEND.
&&
.DISCUSSION...
GRIDS LOOK IN GOOD SHAPE TO START THE DAY SHIFT. WATER VAPOR IMAGERY
DEPICTS PROGRESSIVE SHORT WAVE RIDGING OVER HAWAII. THE NEXT
INCOMING MID LEVEL SHORT WAVE TROUGH IS AMPLIFYING WELL NORTHWEST OF
KAUAI RIGHT NOW MOVING SOUTHWARD ALONG WITH THE ASSOCIATED SURFACE
COLD FRONT. THE MID LEVEL ENERGY WILL FRAGMENT AND AMPLIFY FURTHER
BECOMING POSITIVELY TILTED OVER THE STATE. SHOWER ACTIVITY OVER THE
NORTHWEST PORTION OF THE STATE WILL BEGIN TO GRADUALLY INCREASE
TONIGHT. CHANCES FOR TSTORMS WILL ALSO INCREASE AFTER MIDNIGHT INTO
TOMORROW MORNING AS 500 MB HEIGHTS FALL AND MID LEVEL LAPSE RATES
STEEPEN AHEAD OF THE APPROACHING IMPULSE. ADDITIONAL LOW LEVEL
FORCING AND CONVERGENCE WILL ALSO INCREASE LATE TONIGHT AS THE
WEAKENING SURFACE BOUNDARY APPROACHES THE NORTHWESTERN COASTAL
WATERS. AS LOW LEVEL MOISTURE BEGINS TO INCREASE OVER THE STATE AND
THE COLD POOL ALOFT MIGRATES SLOWLY SOUTHEASTWARD ACROSS THE
FORECAST AREA...THIS WILL TRIGGER SCATTERED HEAVY SHOWERS AND
TSTORMS SUNDAY AFTERNOON INTO MONDAY. TRADES WILL PERSIST AT THE
SURFACE...SO WINDWARD TERRAIN WILL LIKELY BE THE FOCUS OF THE
HEAVIEST SHOWERS/TSTORMS. PLENTY OF SHOWERS WILL BE CARRIED TO
LEEWARD/INTERIOR SECTIONS GIVEN THE ERODED AND LIFTED. THERE WILL BE
CHANCES FOR MIXED FROZEN PRECIP ACROSS THE SUMMITS BEFORE THE
WEEKEND IS OVER AS THE FREEZING LEVEL LOWERS. WILL REVISIT SUMMIT
WEATHER THROUGH THE DAY SHIFT...AS WELL AS TSTORM COVERAGE/TIMING.
AS OF NOW...NOT ANTICIPATING ANY BIG CHANGES TO THE SHORT TERM GRIDS
OTHER THAN SOME MINOR TWEAKS AND HOUSECLEANING.
AS THE UPPER LOW DROPS FURTHER SOUTH...CONDITIONS WILL BEGIN TO
GRADUALLY IMPROVE FROM NORTHWEST TO SOUTHEAST HEIGHTS RISE
ASSOCIATED WITH SHORT WAVE RIDGING AGAIN. CONDITIONS ACROSS THE
STATE WILL BE GETTING BACK TO NORMAL TUESDAY. MODEL SOLUTIONS STILL
AGREE ON ANOTHER POTENT SHORT WAVE APPROACHING THE AREA MID WEEK.
REGARDLESS OF SOME DIFFERENCES IN AMPLITUDE AND THE SURFACE RESPONSE
LOCALLY...THEY DO SUGGEST VEERING LOW LEVEL FLOW WEDNESDAY INTO
THURSDAY WHICH MAY USHER IN DEEPER TROPICAL ITCZ MOISTURE AND A
FRONTAL PASSAGE FRIDAY INTO SATURDAY. DRIER COOLER MID LATITUDE AIR
WILL BE ADVECTED OVER THE STATE IN THE NORTHERLY FLOW BEHIND THE
FRONT OVER THE WEEKEND. NOT PLANNING ANY SIGNIFICANT CHANGES TO THE
LONG TERM RIGHT NOW.
&&
.PREVIOUS DISCUSSION.../ISSUED 400 AM HST SATURDAY MORNING/
SATELLITE IMAGES SHOWED THE MORE FAMILIAR TRADE-WIND SHOWERS AROUND
THE MAIN HAWAIIAN ISLANDS...AND SURFACE DATA REPORTED FURTHER
REDUCTIONS IN WIND SPEEDS DOWN TO A MODERATE LEVEL. PRESSURE TRENDS
WERE DOWN...THOUGH THE NET CHANGE OVER THE PAST 24 HOURS WAS NOT
LARGE. ALTHOUGH GUIDANCE PREDICTS SLIGHT FURTHER DECREASES IN TRADE
WIND SPEEDS TODAY AS THE FRONT TO THE NORTHWEST DISRUPTS THE
SUBTROPICAL RIDGE...THE HIGH IS EXPECTED TO REBUILD VERY QUICKLY
FROM TONIGHT INTO SUNDAY BEHIND THE FRONT...BRINGING THE TRADES
BACK UP AGAIN FROM SUNDAY MORNING INTO MONDAY MORNING.
A SOLID MODEL CONSENSUS STILL SUGGESTS THAT THE NEXT MID-LEVEL
TROUGH WILL START TO DEEPEN OVER THE ISLANDS AS EARLY AS SUNDAY
MORNING...AND PROBABLY WILL CUT OFF INTO A LOW WITH AN IMPRESSIVE
COLD POOL. GUIDANCE DOES DIFFER SIGNIFICANTLY WITH RESPECT TO THE
SOUTHWESTWARD PROGRESS AND INTENSITY OF THIS COLD POOL...BUT AT A
MINIMUM THE LOW WILL PROVIDE UPPER SUPPORT FOR SHOWER DEVELOPMENT.
IF THE COLD POOL FOLLOWS THE MORE SOUTHERLY TRACK FAVORED BY SOME
SOLUTIONS...THEN SOME TRULY EPIC THUNDERSTORMS COULD DEVELOP AROUND
THE STATE FROM SUNDAY AFTERNOON INTO MONDAY MORNING. THE CURRENT
FORECAST TAKES THE MIDDLE ROAD BETWEEN WIDESPREAD THUNDER AND MERELY
ENHANCED SHOWERS...BUT THE OUTSIDE POSSIBILITIES WILL REQUIRE
CONTINUED CONSIDERATION.
THUS...THE WHOLE SCENARIO MAY END UP LOOKING LIKE A REPEAT OF
EARLIER THIS WEEK...WITH MODERATE TO STRONG TRADES...LOCALLY HEAVY
TRADE-WIND SHOWERS...AND THE POTENTIAL FOR CONSIDERABLE THUNDER. THE
FRONT ITSELF IS NOT EXPECTED TO SURVIVE THE COLLISION WITH THE
HIGH...BUT ITS REMNANTS WILL TRAVEL FAR ENOUGH SOUTHEAST TO FEED
THE CONVECTION OVER THE STATE ANYWAY. IT REMAINS TO BE SEEN WHETHER
MODEL PREDICTIONS OF A MOISTURE PLUME FROM THE DEEP TROPICS REACHING
THE STATE DURING THIS SAME TIME WILL MATERIALIZE...BUT IF THEY
PROVE CORRECT...THEN THE CHANCES FOR HEAVY RAIN WILL INCREASE
SUBSTANTIALLY.
THE MORE EXTREME WEATHER PROBABLY WILL WIND DOWN BY WEDNESDAY AS THE
MID-LEVEL LOW LIFTS OUT AGAIN...AND HIGH PRESSURE REESTABLISHES
ITSELF BOTH ALOFT AND AT THE SURFACE TO THE NORTH. MODERATE TRADES
ARE EXPECTED TO RETURN BY THE MIDDLE OF NEXT WEEK WITH MORE TYPICAL
TRADE-WIND SHOWERS...ONLY TO BE REPLACED AGAIN BY WEAK SOUTHERLIES
AHEAD OF AN OSTENSIBLY STRONGER FRONT APPROACHING THE STATE BY NEXT
WEEKEND.
&&
.MARINE...
THE HIGH SURF ADVISORY REMAINS FOR EAST-FACING SHORES OF MOST
ISLANDS. EXPECT THIS SWELL TO LAST AT LEAST UNTIL EARLY SUNDAY. A
NEW NORTHWEST SWELL MAY ARRIVE LATER THIS MORNING...POSSIBLY RAISING
SURF HEIGHTS TO NEAR THE ADVISORY LEVEL ALONG NORTH SHORES...BUT AT
THIS POINT BUOY DATA SUGGEST THAT IT WILL NOT BE LARGE ENOUGH.
HIGH SEAS AND MODERATELY STRONG TRADE WINDS STILL REQUIRE A SMALL
CRAFT ADVISORY FOR TYPICALLY WINDIER AREAS AROUND MAUI COUNTY AND
THE BIG ISLAND...BUT THIS ADVISORY WILL COME DOWN THIS EVENING AS
CONDITIONS BECOME LESS HAZARDOUS THROUGH THE DAY. HOWEVER...THE LULL
WILL NOT LAST LONG...AS WINDS AND SEAS WILL RISE AGAIN OVERNIGHT...
REQUIRING A SMALL CRAFT ADVISORY FOR MOST OF THE COASTAL WATERS BY
SUNDAY NIGHT.
&&
.AVIATION...
VFR WILL BE THE RULE FOR THE TERMINALS TODAY. ANY SHORT LIVED MVFR
CIGS/VIS WILL BE CONFINED MAINLY TO WINDWARD/MT TERRAIN.
TONIGHT...SHRA COVERAGE INCREASES...WITH HIGHER CHANCES FOR
+SHRA/TSRA AFTER 10Z FOR KAUAI/OAHU. CHANCES FOR WIDESPREAD FLIGHT
RESTRICTIONS INCREASE FOR SUNDAY/MONDAY WITH EMBEDDED IFR/LIFR
AROUND THE STRONGER CONVECTION AND SOME WINDWARD SLOPES. AIRMET
TANGO WILL LIKELY REMAIN IN EFFECT FOR A WHILE.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR NIIHAU-KAUAI
WINDWARD-OAHU KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-BIG ISLAND NORTH AND EAST.
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
&&
$$
PUBLIC/AVIATION...DEJESUS
MARINE...DEJESUS/RYSHKO
PREVIOUS...RYSHKO
