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Hawaiian Islands Synoptic Discussion and Guidance

891
FXHW60 PHFO 161333
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED APR 16 2014

.SYNOPSIS...
MODERATE TRADE WINDS WILL CONTINUE THROUGH THE WEEKEND AND INTO NEXT
WEEK...POSSIBLY PEAKING IN STRENGTH AROUND SUNDAY NIGHT. ACTIVE
SHOWERS MOVING IN ON THE TRADES WILL DIMINISH TODAY...AND THEN
INCREASE FROM THURSDAY INTO FRIDAY...BUT THEN EVENTUALLY BECOME
LIMITED MAINLY TO WINDWARD SLOPES.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS STILL REPORTED
MODERATE TO LOCALLY STRONG TRADE WINDS BLOWING. PRECIPITABLE WATER
IN THE AIR MASS WAS NEAR TYPICAL VALUES AROUND THE STATE...AND
SLIGHTLY HIGHER UPWIND...THOUGH DRIER AIR PREVAILED IN MOST OTHER
DIRECTIONS.

THROUGH MOST OF THE NIGHT...A WEAKENING MID-LEVEL TROUGH TO THE
NORTHEAST THROUGH EAST PROVIDED UPLIFT...RAISING THE INVERSION
HEIGHT AND ENCOURAGING SHOWERS PASSING UNDER IT TO DEVELOP MORE THAN
USUAL. THESE SHOWERS THEN TRAINED OVER THE ISLANDS FROM THE EAST.
HOWEVER...AS THE TROUGH WEAKENED GRADUALLY...THIS STREAM OF SHOWERS
DIMINISHED WITH TIME. RAIN RATES APPROACHED MODERATE STRENGTH IN
SOME AREAS...BUT ACCUMULATION OVERALL REMAINED ON THE LIGHT SIDE.

GUIDANCE GENERALLY AGREED THAT THROUGH THE SHORT RUN...MODERATE TO
STRONG...IF FLAT...RIDGING ALOFT EXTENDING OVER THE ISLANDS FROM
THE NORTHWEST WILL EXPAND FURTHER TOWARD THE EAST...WHILE THE TROUGH
WILL CONTINUE TO RECEDE TOWARD THE NORTHEAST. THE RESULTING DEEP
RIDGING THEN WILL PERSIST THROUGH THE REST OF THE FORECAST PERIOD...
DISPLACING THE STORM TRACK TOO FAR NORTH TO HAVE MUCH INFLUENCE ON
THE STATE.

UNDER THESE CONDITIONS...THE SUBTROPICAL RIDGE AT THE SURFACE WILL
RECEIVE ENOUGH SUPPORT FROM ALOFT TO KEEP TRADE WINDS BLOWING
THROUGH THE WEEKEND AND INTO NEXT WEEK. SOLUTIONS DID DIFFER
SOMEWHAT WITH RESPECT TO WIND SPEEDS OVER TIME...BUT THE CONSENSUS
KEPT SPEEDS NEAR MODERATE LEVELS THROUGHOUT...WITH A POSSIBLE PEAK
NEAR SUNDAY NIGHT.

DEEP RIDGING ALSO WILL TEND TO LOWER THE INVERSION HEIGHT OVER
TIME...AND GUIDANCE PREDICTED THE AIR MASS TO DRY A BIT...SO SHOWER
ACTIVITY WILL DIMINISH. HOWEVER...SOLUTIONS SUPPORTED A PLUME OF
MORE HUMID AIR TO TRAIN OVER MAUI AND HAWAII COUNTIES FROM THURSDAY
THROUGH FRIDAY. THUS...POPS AND RELATED FIELDS HAVE BEEN INCREASED
SLIGHTLY THROUGH THIS TIME. ALSO...OROGRAPHIC FORCING WILL CONTINUE
TO SQUEEZE OUT SOME MOISTURE ALONG WINDWARD SLOPES...SO THE
GREATEST DRYING WILL OCCUR MAINLY LEEWARD.

&&

.AVIATION...
THE STRONG TRADE WINDS ARE ON TAP TO CONTINUE STRONG THROUGH TODAY
THOUGH NOT AS STRONG AND GUSTY AS IN PREVIOUS DAYS.

THE MORNING SOUNDING FROM LIH SHOWS A SHARP INVERSION AT 8K. THE
ITO SOUNDING HAS AN INVERSION AT 10K AND NOT AS SHARP AS LIH.
HOWEVER...AN AMDAR SOUNDING FROM KOA AT MIDNIGHT SHOWS A SIMILAR
TEMP PROFILE TO ITO BUT WITH A GOOD VERTICAL WIND SHEAR BTN 8 AND
15K. THUS WILL WE CONTINUE WITH THE CURRENT TURB AIRMETS.

THE AMOUNT OF SHOWER BEARING CLOUDS UPWIND OF THE ISLANDS LOOKS
LESS AREA WIDE COMPARED TO 24 HOURS AGO....BUT IS CONCENTRATED ON
THE HAMAKUA COAST AND HILO PUNA DISTRICTS OF THE BIG ISLAND. WE DO
NOT EXPECT TO IMPOSE AIRMET SIERRA FOR MTN OBSC.

THUS VFR IS THE PREVAILING FLYING WEATHER. THERE WILL BE BRIEF MVFR
CEILINGS AND VIS ASSOCIATED WITH THE SHOWERS RIDING IN WITH THE
TRADES. THESE CLDS AND SHOWERS WILL FAVOR THE WINDWARD AND MTN AREAS
WITH A FEW OF THESE SHOWERS DRIFTING DOWNWIND INTO THE LEEWARD ZONES
OF THE SMALLER ISLANDS. THE KONA CST AND SLOPES WILL HAVE A FEW
AFTERNOON SHOWERS.

&&

.MARINE...
THE SMALL CRAFT ADVISORY /SCA/ WAS EXTENDED THROUGH THIS AFTERNOON
FOR THE CHANNELS AND WATERS AROUND KAUAI AND OAHU...AND CONTINUED
THROUGH FRIDAY FOR TYPICALLY WINDIER AREAS AROUND MAUI AND THE BIG
ISLAND. TRADE WINDS WILL DIMINISH SOMEWHAT TODAY...BUT THEN REMAIN
MODERATE TO FRESH THROUGH FRIDAY. WIND WAVES PRODUCED BY THE
PERSISTENT TRADE WINDS ALSO WILL CONTINUE TO REQUIRE A HIGH SURF
ADVISORY FOR EAST-FACING SHORES THROUGH THIS AFTERNOON.

A SMALL SWELL FROM THE WEST NORTHWEST WILL ARRIVE LATE TODAY...AND
THEN PEAK THURSDAY BELOW THE ADVISORY LEVELS. NO OTHER SIGNIFICANT
SWELLS ARE EXPECTED.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
WINDWARD-OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-
WINDWARD HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-OAHU
WINDWARD WATERS-KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-BIG
ISLAND WINDWARD WATERS.

&&

$$

AVIATION...LAU
REST...RYSHKO



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It was last modified on: Tue, Sep 21 2010 - 2314 UTC
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