Wednesday, April 23, 2014 596-SURF , 596-WAVE , 922-BONG , 638-RUSH , 572-SURF(MAUI) , 241-SURF (KAUAI) , 324-RUSH (BIG ISLAND)
   
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000
FXHW60 PHFO 231356
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED APR 23 2014

.SYNOPSIS...
STRONG RIDGING NORTH OF THE STATE WILL MAINTAIN BREEZY AND GUSTY
TRADE WINDS THROUGH SATURDAY. LOW CLOUDS AND SHOWERS CARRIED BY THE
TRADES WILL REMAIN FOCUSED MAINLY ALONG WINDWARD FACING SLOPES OF
THE ISLAND CHAIN...BUT SOME BRIEF SHOWERS WILL CONTINUE TO BE BLOWN
OVER TO LEEWARD SECTIONS OF THE SMALLER ISLANDS...ESPECIALLY DURING
NIGHTS AND MORNINGS. A SLIGHT INCREASE IN SHOWERS IS EXPECTED ACROSS
PARTS OF THE STATE LATE THURSDAY. THE TRADE WIND SPEEDS ARE FORECAST
TO GRADUALLY DECLINE FROM SUNDAY INTO EARLY NEXT WEEK.

&&

.DISCUSSION...
A 1028 MB SURFACE HIGH CENTERED NEAR 32N 142W...OR MORE THAN 1250
MILES NORTHEAST OF HONOLULU...IS MOVING TOWARD THE SOUTHEAST AT
ABOUT 10 MPH. A SURFACE RIDGE EXTENDS WEST FROM THIS HIGH THROUGH A
POINT ABOUT 650 MILES NORTH OF HONOLULU. THE RELATIVELY TIGHT
PRESSURE GRADIENT SOUTH OF THESE FEATURES CONTINUES TO MAINTAIN
BREEZY AND LOCALLY GUSTY TRADE WINDS ACROSS THE MAIN HAWAIIAN
ISLANDS EARLY THIS MORNING.

ALOFT...THE CLOSE PROXIMITY OF A STRONG MID-TROPOSPHERIC ANTICYCLONE
NORTHEAST OF THE ISLANDS IS MAINTAINING STABLE ATMOSPHERIC
CONDITIONS ACROSS THE REGION TONIGHT. AS A RESULT...THE LOW-LEVEL
TRADE WIND INVERSION IS AROUND 6 THOUSAND FEET. THIS RELATIVELY LOW
INVERSION HEIGHT HAS CONTRIBUTED TO MAINTAINING THE GUSTY TRADE
WINDS ACROSS PARTS OF THE STATE TONIGHT. THIS IS ESPECIALLY TRUE IN
VALLEYS DOWNWIND OF HIGHER TERRAIN...SUCH AS THE KOOLAU MOUNTAIN
RANGE ON OAHU. SATELLITE IMAGERY AND RADAR REFLECTIVITY DATA ALSO
SHOW LIMITED SHOWER BEARING CLOUDS OVER AND IMMEDIATELY UPSTREAM OF
THE STATE. THEREFORE...THE STABLE CONDITIONS DUE TO THE
MID-TROPOSPHERIC ANTICYCLONE ARE LIKELY CONTRIBUTING TO THE
REDUCTION OF RAINFALL OVER MOST OF THE REGION. NOTE THAT THE
PRESENCE OF AN UPPER TROPOSPHERIC TROUGH NEAR KAUAI CONTINUES TO
SEND PATCHES OF CIRRUS UP OVER PARTS OF THE ISLAND CHAIN THIS
MORNING.

THE FORECAST MODELS INDICATE STRONG SURFACE RIDGING WILL CONTINUE
NORTH OF THE ISLANDS BETWEEN LATITUDES 30N AND 35N INTO SATURDAY.
THE TIGHT PRESSURE GRADIENT SOUTH OF THIS RIDGING WILL KEEP THE
TRADE WINDS BREEZY AND GUSTY. ALSO...THE STRONG MID-TROPOSPHERIC
RIDGING OVER THE REGION WILL MAINTAIN STABLE ATMOSPHERIC CONDITIONS
THROUGH THE END OF THE WORK WEEK. AT THE SAME TIME...THE LOW-LEVEL
TRADE WIND INVERSION WILL CAUSE PERIODS OF ENHANCED WIND GUSTS OVER
AND DOWNWIND OF HIGHER TERRAIN ACROSS PARTS OF THE STATE. IN
FACT...THE GFS AND ECMWF MODELS SUGGEST THERE MAY BE ANOTHER
INCREASE IN 850 MB WINDS BY LATE THURSDAY AT THE SAME TIME A NEW
SURFACE HIGH PASSES NORTH OF THE STATE. THIS COULD LEAD TO ANOTHER
ROUND OF STRONG TRADE WINDS...WHICH MAY REQUIRE THE ISSUANCE OF WIND
ADVISORIES FOR PARTS OF THE STATE.

THE FORECAST GUIDANCE INDICATES WE SHOULD CONTINUE TO HAVE A RATHER
TYPICAL TRADE WIND WEATHER PATTERN WITH LOW CLOUDS AND SHOWERS
MAINLY AFFECTING WINDWARD FACING SLOPES. HOWEVER...THE REMNANT
MOISTURE FROM A DECAYING FRONT EAST NORTHEAST OF THE STATE WILL
LIKELY RIDE IN ON THE INCREASING LOW-LEVEL TRADE WIND FLOW BY LATE
THURSDAY. AS A RESULT...A SLIGHT INCREASE IN PRECIPITATION OVER
WINDWARD AND MAUKA AREAS THURSDAY...ESPECIALLY THURSDAY NIGHT. AT
THE SAME TIME...THE STRENGTHENING TRADE WINDS MAY CARRY SOME BRIEF
SHOWERS OVER TO LEEWARD SECTIONS OF SOME OF THE SMALLER ISLANDS...
ESPECIALLY DURING THURSDAY NIGHT AND EARLY FRIDAY MORNING. BESIDES
THE POTENTIALLY WETTER CONDITIONS LATE THURSDAY...THE FORECAST
GUIDANCE DOES NOT SHOW ANY OTHER ORGANIZED SYSTEM WITH ENHANCED
COVERAGE OF SHOWERS MOVING INTO THE AREA THROUGH THIS WEEKEND.

THE UPPER LEVEL TROUGH IS FORECAST TO CONTINUE TO WEAKEN AND LIFT
OUT TO THE NORTHEAST LATER TODAY AND TONIGHT...WHICH IS EXPECTED TO
DIMINISH THE COVERAGE OF CIRRUS CLOUDS NEAR THE ISLANDS. HOWEVER...A
NEW UPPER LEVEL TROUGH MOVING INTO THE VICINITY OF THE MAIN HAWAIIAN
ISLAND CHAIN THIS WEEKEND MAY PRODUCE WIDESPREAD HIGH CLOUDS OVER
PARTS OF THE STATE AGAIN STARTING SATURDAY.

THE LONGER RANGE FORECAST MODELS INDICATE THE TRADE WIND SPEEDS WILL
BEGIN TO DECREASE FROM LATE THIS WEEKEND INTO EARLY NEXT WEEK AS THE
SURFACE RIDGE TO THE NORTH OF THE AREA WEAKENS. NOTE THAT RECENT
RUNS OF THE ECMWF MODEL WEAKEN THE WINDS MORE THAN THE MOST RECENT
RUNS OF THE GFS MODEL. THE CURRENT FORECAST IS A BLEND OF THESE
MODELS...SO THERE MAY BE SOME ADJUSTMENT UP OR DOWN TO THE TRADE
WIND SPEEDS EARLY NEXT WEEK ONCE THE MODELS START TO COME INTO
BETTER AGREEMENT IN THE NEXT FEW DAYS.

THE TRADE WIND WEATHER PATTERN IS EXPECTED TO CONTINUE FROM SUNDAY
INTO EARLY NEXT WEEK...WITH MAINLY WINDWARD AND MAUKA SHOWERS.
HOWEVER...A WEAKENING FRONTAL BAND MAY MOVE SOUTHWARD AND REACH THE
STATE NEXT WEEK. BASED ON THE LATEST GUIDANCE...THIS FEATURE MAY
ENHANCE RAINFALL ACROSS MANY AREAS OF THE STATE STARTING LATE
TUESDAY OR WEDNESDAY OF NEXT WEEK.

&&

.AVIATION...
LOW CLOUDS AND SHOWERS CARRIED BY THE MODERATE TRADE WINDS WILL
AFFECT MAINLY WINDWARD AND MOUNTAIN AREAS...THOUGH WINDS ARE STRONG
ENOUGH FOR SOME OF THESE SHOWERS TO REACH LEE AREAS OF THE SMALLER
ISLANDS. VFR CONDITIONS WILL PREVAIL FOR ALL SITES...THOUGH PASSING
LOW CLOUDS AND SHOWERS MAY BRING BRIEF MVFR CEILING OR EVEN IFR
CEILING CONDITIONS MAINLY FOR THE WINDWARD SITES.

AIRMET TANGO FOR MECHANICAL TURBULENCE TO THE LEE OF MOUNTAINS
CONTINUES TODAY DUE TO THE WINDS.

&&

.MARINE...
THE FRESH TO LOCALLY STRONG TRADE WINDS CONTINUE TO REQUIRE A SMALL
CRAFT ADVISORY /SCA/ REMAIN IN EFFECT FOR ALL HAWAIIAN CHANNELS AND
THE TYPICALLY WINDY WATERS ADJACENT TO THE BIG ISLAND AND MAUI.
SINCE THE TRADE WINDS WILL LIKELY REMAIN STRONG THROUGH THE
REMAINDER OF THE WORK WEEK...THE SCA IS CURRENTLY IN'EFFECT FOR
THESE WATERS THROUGH FRIDAY. NOTE THAT THERE MAY BE A SLIGHT
INCREASE IN WINDS BY LATE THURSDAY THURSDAY...SO ADDITIONAL HAWAIIAN
WATERS MAY NEED TO BE ADDED TO THE SCA FROM THURSDAY NIGHT INTO
FRIDAY. THE FORECAST GUIDANCE SUGGESTS THERE MAY BE A SLOW
DECREASING TREND IN WINDS FROM LATE SATURDAY INTO EARLY NEXT
WEEK...SO THE SCA MAY EVENTUALLY BE DROPPED FOR MOST OR ALL HAWAIIAN
WATERS BY SUNDAY OR MONDAY.

THE ROUGH ELEVATED SURF CONTINUES JUST BELOW THE HIGH SURF ADVISORY
THRESHOLD ALONG EAST FACING SHORES. THE MOST RECENT OBSERVATIONS
FROM THE COASTAL BUOYS NEAR WINDWARD SHORELINES OF THE ISLANDS HAVE
BEEN SHOWING SIGNIFICANT WAVE HEIGHTS OF 7 TO 8 FEET WITH A PERIOD 8
TO 9 SECONDS. THE WAVE WATCH III MODEL GUIDANCE SUGGESTS THERE WILL
BE LITTLE VARIATION IN THESE WAVE HEIGHTS AND PERIODS INTO SATURDAY.
SURF HEIGHTS ARE EXPECTED TO GRADUALLY DIMINISH ALONG EAST FACING
SHORES FROM SATURDAY NIGHT THROUGH MONDAY.

ELSEWHERE...THE NEW LONG-PERIOD NORTHWEST SWELL HAS ARRIVED AT BUOY
51101 NORTHWEST OF KAUAI. FORERUNNERS FROMM THIS NEW SWELL HAVE ALSO
ARRIVED AT THE HANALEI BUOY NEAR THE NORTH SHORE OF KAUAI. THIS
SWELL WILL GRADUALLY BUILD ACROSS EXPOSED NORTH AND WEST FACING
SHORES OF THE ISLANDS TODAY...AND PEAK ON THURSDAY. THE WAVE WATCH
III MODEL INDICATES SURF PRODUCED BY THIS SWELL WILL REMAIN BELOW
THE HIGH SURF ADVISORY CRITERIA ALONG NORTH AND WEST FACING SHORES
OF THE SMALLER ISLANDS. HOWEVER...WE WILL MONITOR THE BUOY
OBSERVATIONS IN CASE THE SWELL IS LARGER THAN FORECAST. THIS
NORTHWEST SWELL WILL GRADUALLY SUBSIDE FROM FRIDAY THROUGH SATURDAY.
NO OTHER SIGNIFICANT SWELLS ARE EXPECTED THROUGH NEXT TUESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR ALL HAWAIIAN
CHANNELS...MAALAEA BAY AND THE WATERS SOUTH OF THE BIG ISLAND.

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...HUI





THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD

HAWAII EXTENDED FORECAST DISCUSSION




HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
756 AM EDT WED APR 23 2014

VALID 00Z THU APR 24 2014 - 00Z THU MAY 01 2014

MODELS AND ENSEMBLES DISPLAY RELATIVELY GOOD AGREEMENT AND
CONTINUITY THROUGH ABOUT SAT.  HIGH PRESSURE NEAR 30-35N LATITUDE
WILL SUPPORT MODERATE TO BRISK TRADES WITH RNFL TENDING TO FAVOR
WINDWARD TERRAIN.  A MODEST WEAKNESS ALOFT COULD SUPPORT SLIGHT
ENHANCEMENT OF ACTIVITY INTO THU WITH A RIDGE ALOFT JUST NW/N OF
THE ISLANDS EXPANDING SOMEWHAT BRIEFLY THEREAFTER.  TRADES SHOULD
BEGIN TO TREND LIGHTER DURING THE WEEKEND AS HIGH PRESSURE
WEAKENS.  FROM SUN ONWARD THERE ARE CONTINUING DIFFS WITH THE
DEGREE OF CNTRL-ERN PAC TROUGH AMPLIFICATION WHICH LEAD TO SPREAD
WITH THE TIMING/SWD EXTENT OF THE ASSOC SFC FRONT THAT MAY REACH
THE ISLANDS DURING THE FIRST HALF OF NEXT WEEK.  IN A REVERSAL
FROM 24 HRS AGO THE 00Z/06Z GFS RUNS ARE NOW ON THE MORE AMPLIFIED
SIDE OF THE SPREAD WITH THE TROUGH ALOFT AND FASTER/FARTHER SWD
WITH THE SFC FRONT RELATIVE TO THE 00Z ECMWF/ECMWF MEAN.  THE MOST
CONSISTENT INTERMEDIATE SOLN AT THIS TIME APPEARS TO BE A
COMPROMISE BETWEEN THE 00Z GEFS MEAN AND 00Z ECMWF/ECMWF MEAN. 
HIGH PRESSURE BUILDING IN BEHIND THIS FRONT WILL LIKELY SERVE TO
STRENGTHEN TRADES SOMEWHAT BY TUE-WED.

RAUSCH





Last Updated: 756 AM EDT WED APR 23 2014




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