Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 240625
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED APR 23 2014

.SYNOPSIS...
BREEZY AND GUSTY TRADE WINDS WILL STRENGTHEN GRADUALLY INTO
FRIDAY...AND THEN DIMINISH FROM SUNDAY INTO NEXT WEEK. A MOISTER
AIR MASS WILL BRING MORE SHOWERS AROUND FRIDAY...BUT OTHERWISE
RAINFALL WILL BE LIGHT...AND FOCUSED MAINLY OVER WINDWARD SLOPES...
THOUGH THE WIND WILL CARRY SOME SHOWERS LEEWARD BEFORE THEY
DISSIPATE.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED
MODERATE TO STRONG TRADE WINDS BLOWING...WHILE PRESSURE TRENDS
SUGGESTED A SLIGHT INCREASE IN SPEEDS THROUGH THE SHORT RUN. CLOUD
COVER WAS ON THE LOW SIDE OF USUAL UPWIND OF THE STATE...AND SO
UNSURPRISINGLY MOST PRECIPITATION OVER LAND REMAINED LIMITED MAINLY
TO WINDWARD SLOPES...WHERE IT RECEIVED SUPPORT FROM OROGRAPHIC
FORCING. THREE-HOUR ACCUMULATION VARIED FROM BARELY ANY...TO NEARLY
A THIRD OF AN INCH...LIKELY INFLUENCED BY MINOR DIFFERENCES IN THE
WIND...LOCAL TOPOGRAPHY...AND THE ARRIVAL OF EXISTING SHOWERS FROM
UPWIND.

ALOFT...WEAK TROUGHING TO THE SOUTHWEST MOVED FURTHER AWAY FROM THE
ISLANDS...WHILE BROAD RIDGING EXPANDED OVER THE STATE FROM THE
NORTHWEST. GUIDANCE PREDICTED THIS MID-LEVEL RIDGE TO PERSIST
THROUGH ABOUT SATURDAY...PROVIDING SUBSTANTIAL SUPPORT TO THE
SUBTROPICAL RIDGE AT THE SURFACE TO THE NORTHEAST...AND INCREASING
LOCAL STABILITY CONSIDERABLY. SINCE WIND SPEEDS AT MANY LOCATIONS
STILL REMAINED CLOSE TO THE CRITERION FOR A WIND ADVISORY...THIS
PRODUCT MAY WELL BE NEEDED AT SOME POINT AS THE WINDS INCREASE.

IN ANY CASE...DRY TRADE-WIND CONDITIONS WILL PREVAIL. HOWEVER...
INCREASED WIND SPEEDS WILL CONTINUE TO SQUEEZE OUT AT LEAST A LITTLE
RAIN OVER WINDWARD SLOPES...ESPECIALLY FROM FRIDAY INTO FRIDAY
NIGHT...WHEN MOST SOLUTIONS PREDICTED A SOMEWHAT MOISTER AIR MASS TO
PASS.

FROM LATE SUNDAY INTO THE EARLY PART OF NEXT WEEK...THE RIDGE ALOFT
WILL SHIFT QUITE FAR EAST...LIMITING ITS INFLUENCE LOCALLY. SOME
MODELS HINTED THAT THE OLD MID-LEVEL LOW MAY RETURN FROM THE WEST AS
AN OPEN...IF SHALLOW...TROUGH ON A BROADER AND DEEPER TROUGH
APPROACHING FROM THE NORTH NORTHWEST. THIS LATE IN THE SEASON...THE
DEEPER TROUGH WILL BE VERY UNLIKELY TO HAVE MUCH LOCAL EFFECT...BUT
THE SHALLOWER ONE MAY BE ABLE TO WEAKEN THE SUBTROPICAL RIDGE...AND
THUS THE TRADE WINDS...THROUGH THIS PERIOD. BY THE TIME THAT THE
SURFACE FRONT ASSOCIATED WITH THE DEEPER TROUGH ARRIVES AROUND
WEDNESDAY...IT SHOULD BE LIMITED TO LITTLE MORE THAN A SLIGHT WIND
SHIFT...AND A BIT OF CONVERGED MOISTURE SUPPORTING THE WINDWARD
SHOWERS. MORE TYPICAL TRADE WINDS WILL PREVAIL THROUGH THE SECOND
HALF OF NEXT WEEK.

&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ REMAINED IN EFFECT FOR ALL WATERS IN
ANTICIPATION OF STRENGTHENING WINDS AND BUILDING COMBINED SEAS
THROUGH FRIDAY AFTERNOON...BUT MAY BE REDUCED IN AREA TO THE
TYPICALLY WINDY WATERS AROUND THE BIG ISLAND AND MAUI ON SATURDAY
NIGHT OR SUNDAY. THE NORTHEASTERLY WINDS WILL REACH THEIR MINIMUM
SPEEDS LATE SUNDAY OR MONDAY...AND THEN INCREASE AGAIN BY THE MIDDLE
OF NEXT WEEK.

THE PERSISTENT TRADE WINDS WILL BUILD SEAS...PRODUCING ROUGH SURF
NEAR THE ADVISORY LEVEL ALONG EAST-FACING SHORES BY FRIDAY. THE
INCREASING SEAS ALSO WILL CONTRIBUTE TO THE NEED FOR AN EXPANDED
SCA. SEAS WILL DIMINISH WITH THE WINDS LATE SATURDAY AND
SUNDAY.

A NORTHWEST SWELL WILL CONTINUE TO BUILD THIS EVENING...PRODUCING
SIGNIFICANT WAVE HEIGHTS JUST BELOW THE NORTH-SHORE ADVISORY
CRITERION ON THE SMALLER ISLANDS LATE TONIGHT AND THURSDAY. THE
SWELL WILL DROP FRIDAY AND SATURDAY...BUT A SMALL REINFORCING
NORTHWEST SWELL MAY ARRIVE LATE SUNDAY INTO TUESDAY.

SOUTH-FACING SHORES HAVE BEEN RECEIVING SOME SWELL ENERGY FROM THE
SOUTHWEST. THIS SWELL WILL FADE ON FRIDAY...BUT SMALL SWELL FROM
THE SOUTH SOUTHEAST MAY ARRIVE OVER THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR ALL HAWAIIAN
WATERS-

&&

$$

RYSHKO




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