Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 050619
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED MAR 4 2015

.SYNOPSIS...
THE CLOUD BAND OVER THE STATE WILL SHIFT SOUTHEAST TONIGHT...
LIMITING MOST OF ITS RAIN TO MAUI AND HAWAII COUNTIES AFTER ABOUT
MIDNIGHT. A COOLER AND DRIER AIR MASS WILL PREVAIL OVER KAUAI
COUNTY...AND OAHU AFTER MIDNIGHT. THE RAIN AND CLOUDS OVER THE
SOUTHEAST END OF THE STATE WILL DIMINISH GRADUALLY THROUGH THE
WEEKEND. NORTHEAST WINDS WILL PERSIST THROUGHOUT. A SIMILAR RAIN
BAND MAY AFFECT THE STATE EARLY NEXT WEEK.

&&

.DISCUSSION...
DEEP CLOUD LAYERS BLANKETED THE MAIN HAWAIIAN ISLANDS FROM OAHU TO
THE BIG ISLAND. ALTHOUGH NO FRONT AS SUCH WAS PRESENT...THE AIR MASS
CHANGED RAPIDLY WITH DISTANCE FROM THE RELATIVELY MOIST AND WARM AIR
MASS OVER THE BIG ISLAND...TO THE RELATIVELY DRY AIR MASS OVER
KAUAI. ALOFT...A LOCALLY SHARP EXTENSION OF THE BROADER TROUGH
LOCATED WELL TO THE NORTHEAST PROVIDED LIMITED DYNAMIC UPLIFT...BUT
ITS IMPRESSIVE COLD POOL LIKELY CONTRIBUTED MORE TO THE INSTABILITY
DRIVING THE WEATHER ACROSS THE STATE. WINDS WERE A LITTLE TOO
NORTHERLY TO BE CALLED PROPER TRADE WINDS...AND SPEEDS TOO HIGH TO
BE CALLED TYPICAL.

THROUGH TONIGHT...GUIDANCE PREDICTED THE DEEP CLOUD LAYERS TO SHIFT
SOUTHEAST...AND SATELLITE IMAGES CERTAINLY SUPPORTED SUCH A TREND.
OAHU SHOULD FOLLOW KAUAI INTO THE DRIER...COOLER SECTOR DURING THE
NEXT FEW HOURS. UNTIL THEN...SHOWERS STILL MAY OCCUR ALONG THE BACK
EDGE OF THE CLOUD BAND. SOLUTIONS AGREED SURPRISINGLY WELL THAT THE
SHORT WAVE ON THE MID-LEVEL TROUGH WILL SHIFT TO THE EAST END OF THE
STATE...SO THE SLIGHT CHANCE OF THUNDERSTORMS AROUND THE BIG ISLAND
STILL SEEMED PRUDENT...ALONG WITH A RISK OF HEAVY RAIN. HOWEVER...BY
THURSDAY MORNING MOST OF THE PRECIPITATION SHOULD BECOME LIMITED TO
STRATUS RAIN.

IT WAS LESS CLEAR HOW SOON THE DEEP CLOUD LAYERS WILL LEAVE MAUI
COUNTY AND THE BIG ISLAND. GOING BACK AS FAR AS LAST WEEK...
SOLUTIONS HAVE TENDED TO PORTRAY A MORE GRADUAL DECREASE IN
PRECIPITATION AND CLOUD COVER THERE. BASED ON THIS HISTORY...
INCLUDING RECENT RUNS...THE OFFICIAL FORECAST FOR THE SOUTHEAST
COUNTIES MAY BE TOO DRY AND CLEAR TOO SOON. ONE ALTERNATIVE
POSSIBILITY MAY BE THAT THE CLOUD LAYERS WILL FRAY GRADUALLY THROUGH
THE REST OF THE WEEK AND INTO THE WEEKEND...WITH SHOWERS DIMINISHING
EQUALLY SLOWLY THROUGH THIS PERIOD.

IN ANY CASE...KAUAI COUNTY AND OAHU WILL SPEND MOST OF THE REST OF
THE WEEK UNDER THE COLD-AIR CUMULI. ALTHOUGH HEAVY SHOWERS WILL BE
UNLIKELY THERE AFTER TONIGHT...OROGRAPHIC FORCING MAY BE ABLE TO
SQUEEZE OUT SOME RAIN FROM THE COOL AIR MASS OVER WINDWARD SLOPES.
ACCUMULATION WILL BE LIGHT...BUT POPS AS SUCH AND CLOUD COVER MAY
NEED A BOOST IN PREFERRED AREAS.

A PAIR OF FRONTS CRASHING INTO THE SURFACE HIGH TO THE NORTH WILL
DIMINISH WIND SPEEDS OVER THE STATE THROUGH THE NEXT 72 HOURS...BUT
WIND DIRECTION SHOULD REMAIN A LITTLE TO THE NORTH OF CLIMATOLOGY.

UNSURPRISINGLY...SOLUTIONS STARTED TO DRIFT APART BY EARLY NEXT
WEEK. HOWEVER...SOME MODELS PREDICTED A LOBE OF THE MID-LEVEL LOW TO
SWEEP OVER THE ISLANDS AGAIN...PROVIDING UPLIFT AND REDUCING
STABILITY. GUIDANCE DID AGREE THAT WATER VAPOR WOULD ACCUMULATE
ALONG THE BOUNDARY BETWEEN THE AIR MASSES AGAIN BY THAT TIME. THE
SUPPORT FROM ALOFT MAY ENABLE THE BOUNDARY TO SHIFT NORTH OVER THE
STATE AGAIN...POTENTIALLY BRINGING A REPEAT OF THE PAST FEW DAYS.

&&

.MARINE...
A SLIGHT CHANCE OF THUNDERSTORMS WILL CONTINUE OVER THE COASTAL
WATERS AROUND THE BIG ISLAND AND MAUI THROUGH TONIGHT. A SMALL CRAFT
ADVISORY WAS IN EFFECT FOR STRONG TRADE WINDS AND ROUGH SEAS OVER
TYPICALLY WINDIER COASTAL WATERS. ROUGH SURF WILL BUILD ALONG
EAST-FACING SHORES LATER IN THE WEEK...POSSIBLY REQUIRING A HIGH
SURF ADVISORY. A NORTH SWELL ARRIVING SUNDAY MAY PRODUCE ADVISORY-
LEVEL SURF ALONG NORTH-FACING SHORES. OTHERWISE...SURF IS EXPECTED
TO REMAIN BELOW THE ADVISORY THRESHOLDS THROUGH THE WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 6 AM HST THURSDAY FOR MAUI-KONA-SOUTH
BIG ISLAND-BIG ISLAND NORTH AND EAST-KOHALA-BIG ISLAND INTERIOR.

WINTER STORM WARNING UNTIL 6 AM HST THURSDAY FOR BIG ISLAND
SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-KAIWI CHANNEL-MAALAEA
BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-
BIG ISLAND SOUTHEAST WATERS.

&&

$$

RYSHKO




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