Weather Service Report


230 
FXHW60 PHFO 260612
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SAT APR 25 2015

.SYNOPSIS...
A SLOW-MOVING FRONT WILL SPREAD MODEST RAIN FROM KAUAI TO THE BIG 
ISLAND THROUGH MONDAY NIGHT. LIGHT SOUTHEAST WINDS AHEAD OF THE 
FRONT WILL TURN DIRECTLY INTO BREEZY TRADE WINDS BEHIND IT. THE 
TRADE WINDS WILL CONTINUE TO BRING ACTIVE SHOWERS TO WINDWARD SLOPES 
THROUGH MOST OF THE COMING WEEK.

&&

.DISCUSSION...
A SLOW-MOVING FRONTAL CLOUD BAND MOVED FROM EAST TO WEST ACROSS 
KAUAI...WHILE LIMITED AFTERNOON CONVECTION PREVAILED IN THE LIGHT 
SOUTHEAST FLOW OVER THE REST OF THE STATE. ALTHOUGH CONVERGENCE 
BETWEEN SOUTHEAST AND MORE SOUTHERLY OR SOUTHWESTERLY WINDS OFTEN 
SUPPORTS SHOWER DEVELOPMENT AS A FRONT APPROACHES THE STATE...IN 
THIS CASE THE PRE-FRONTAL AIR MASS PROVIDED RELATIVELY LITTLE WATER 
VAPOR. ALOFT...A WELL-DEFINED LOW TO THE NORTH OF THE STATE MIRRORED 
THE SURFACE LOW TO WHICH THE FRONT WAS ATTACHED...BUT MOST OF THE 
DYNAMIC SUPPORT WAS FOCUSED WELL NORTH OF 25N.

THOUGH OCCASIONAL TOWERING CUMULI ROSE THROUGH THE SURROUNDING 
LAYERS OF THE CLOUD BAND EVEN SOUTH OF 20N...NEAR THE ISLANDS THE 
MAIN STRENGTH OF THIS FEATURE WAS CONCENTRATED IN A THIN AND ROPY 
LINE OF SHOWERS. DESPITE TRAINING FOR HOURS THIS AFTERNOON OVER 
KAUAI...THE BAND DROPPED ONLY MODEST PRECIPITATION...AND PROBABLY 
WILL DO NO MORE OVER OAHU ON SUNDAY. CONVECTIVE SHOWERS ALONG THE 
FRONT...OR FROM CONVERGENCE IN THE PRE-FRONTAL SECTOR...LIKELY WILL 
BE THE MAIN CONCERN. IN ANY CASE...THE SHOWER BAND SHOULD REACH OAHU 
BY SUNDAY AFTERNOON...MAUI COUNTY BY SUNDAY EVENING...AND THEN THE 
BIG ISLAND BY MONDAY EVENING. SLOWLY DISSIPATING CLOUD LAYERS WILL 
OBSCURE THE SKY AND DROP A FEW SPRINKLES ON BOTH SIDES OF THE MAIN 
RAIN BAND.

GUIDANCE AGREED WELL IN PREDICTING THE SUPPORTING MID-LEVEL LOW TO 
LIFT OUT RAPIDLY TOWARD THE NORTHEAST THROUGH THE NEXT 24 HOURS... 
LEAVING ONLY A SHALLOW TROUGH TO SUPPORT THE WEAKENING FRONT. SOLID 
RIDGING ALOFT BUILDING IN FROM THE NORTHWEST WILL SUPPORT THE RAPID 
DEVELOPMENT OF THE SURFACE HIGH BEHIND THE FRONT...BRINGING MODERATE 
TO STRONG WINDS SHORTLY AFTER FRONTAL PASSAGE. THESE WINDS WILL HAVE 
MORE OF AN EASTERLY COMPONENT THAN IS USUAL IN SUCH CASES...SO ONE 
COULD SAY SIMPLY THAT MODERATE TO STRONG TRADE WINDS WILL RETURN TO 
NEARLY ALL OF THE STATE BY MONDAY EVENING...AND THEN PERSIST THROUGH 
MOST OF THE COMING WEEK.

AS THE FRONTAL CLOUD BAND FALLS APART...IT WILL SHED ITS LOAD OF 
WATER VAPOR ONTO THE TRADES. THE WINDS IN TURN WILL CARRY THIS MOIST 
AIR MASS OVER THE STATE AGAIN...PRODUCING CONTINUED RAINFALL OVER 
WINDWARD SLOPES. THUS...CONDITIONS WILL REMAIN ON THE WET SIDE OF 
USUAL THROUGH THE FORECAST PERIOD.

&&

.MARINE...
SURF ALONG SOUTH- AND EAST-FACING SHORES WILL SUBSIDE THROUGH THE 
REST OF THE WEEKEND AS THE WINDS AND SOUTH-SOUTHWEST SWELL TAPER 
OFF. A LARGER NORTH-NORTHWEST SWELL SHOULD ARRIVE SUNDAY NIGHT...AND 
THEN BECOME MORE NORTHERLY BY MONDAY NIGHT. THIS SWELL LIKELY WILL 
PRODUCE SURF ABOVE THE ADVISORY THRESHOLD ALONG NORTH-FACING SHORES 
BY MONDAY...AND ALONG EAST-FACING SHORES BY LATE MONDAY OR TUESDAY 
AS THE SWELL DIRECTION BECOMES MORE NORTHERLY.

SOUTH TO SOUTHEAST WIND SPEEDS SHOULD REMAIN BELOW THE THRESHOLD 
FOR A SMALL CRAFT ADVISORY THROUGH SUNDAY. HOWEVER...STRONG 
NORTHEAST WINDS BEHIND THE FRONT WILL SPREAD SCA CONDITIONS 
SOUTHEAST ALONG THE ISLAND CHAIN FROM KAUAI TO THE BIG ISLAND FROM 
SUNDAY EVENING THROUGH MONDAY NIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

RYSHKO



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