Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 180127
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
327 PM HST FRI APR 17 2015

.SYNOPSIS...
HIGH PRESSURE NORTH OF THE STATE WILL KEEP FRESH TO LOCALLY STRONG TRADE
WINDS ACROSS HAWAII INTO TUESDAY. ISOLATED TO SCATTERED SHOWERS
WILL FOCUS OVER THE WINDWARD AND MAUKA AREAS WITH STABLE CONDITIONS
ALOFT KEEPING RAINFALL ACCUMULATIONS LIGHT. AN UPPER TROUGH AND COLD
FRONT NORTHWEST OF THE AREA APPROACH HAWAII AND WEAKEN THE TRADES
DURING THE MIDDLE TO LATTER PART OF NEXT WEEK.

&&

.DISCUSSION...
DRIER AND MORE STABLE CONDITIONS HAVE MOVED OVER THE HAWAIIAN ISLANDS
THIS AFTERNOON AS UPPER LEVEL RIDGING BEGINS TO MOVE IN FROM THE WEST.
CURRENT VISIBLE SATELLITE SHOWS MORE SUNSHINE OVER THE STATE WITH
A SOME LOW LEVEL CLOUD BUILD UPS ACROSS WINDWARD SIDES OF THE SMALLER
ISLANDS...AND LEEWARD AREAS OF HALEAKALA AND BIG ISLAND. SOUNDINGS
FROM THIS AFTERNOON SHOW A STRENGTHENING INVERSION AT LIHUE AND
PRECIPITABLE WATER VALUES OF 0.94 INCHES. THE HILO SOUNDING SHOWS
AN ELEVATED INVERSION...BUT PRECIPTABLE WATER VALUES HAVE DROPPED
OFF SINCE THIS MORNING...SHOWING 1.07 INCHES.

HIGH PRESSURE WILL REMAIN NORTH OF HAWAII INTO THE FIRST HALF OF
NEXT WEEK AND WILL KEEP THE TRADE WINDS BLOWING. THE CURRENT HIGH
IS LOCATED FAR NORTHEAST OF THE STATE...AND WILL BE REPLACED BY
ANOTHER HIGH NORTHWEST OF THE STATE THAT WILL TRACK EASTWARD
MONDAY AND TUESDAY. THE PRESSURE GRADIENT OVER THE ISLANDS WILL
TIGHTEN TONIGHT...ALLOWING WINDS TO BOOST UP TO FRESH TO LOCALLY
STRONG THROUGH TUESDAY. RIDGING ALOFT WILL KEEP THE ATMOSPHERE
STABLE DURING THIS TIME...LIKELY RESULTING IN ONLY A FEW WINDWARD
AND MAUKA SHOWERS.

THE NEXT WEATHER SYSTEM...A COLD FRONT WITH SOME UPPER LEVEL SUPPORT...WILL
APPROACH THE ISLANDS FROM THE NORTHWEST TUESDAY NIGHT. EXPECT THE
TRADES TO WEAKEN AND VEER TO THE SOUTHEAST TUESDAY NIGHT AND
WEDNESDAY. BOTH GFS AND ECMWF KEEP MOST OF THE ENERGY AND MOISTURE
ASSOCIATED WITH THIS SYSTEM TO THE NORTH OF THE STATE THROUGH THE
SECOND HALF OF THE WEEK. HOWEVER...MODELS DISAGREE ON WHETHER TO
LIFT THE LOW AWAY FROM THE AREA OR SLOW THE SYSTEM DOWN NORTHWEST
OF THE AREA. THIS DIFFERENCE IN MODEL SOLUTIONS WILL AFFECT THE
WIND PATTERN OVER THE STATE DURING THIS TIME. CONFIDENCE IN THE
MODEL DETAILS DEGRADES IN THE LONG TERM...AND WILL CONTINUE TO
MONITOR THIS WEATHER SYSTEM IN THE COMING DAYS.


&&

.AVIATION...
BREEZY TRADE WINDS WILL KEEP CLOUDS AND SHOWERS FOCUSED ACROSS
MAINLY WINDWARD SECTIONS. CONDITIONS HAVE DRIED OUT SINCE THIS
MORNING...BUT OCCASIONAL MVFR CONDITIONS ARE STILL EXPECTED IN
SHOWERS.

RADAR VAD WIND PROFILES AND 00Z SOUNDINGS SHOW WINDS HAVE DROPPED
OFF A BIT TO 20 KT...BUT THE 18Z GFS SHOWS THIS AS A BRIEF LULL
BEFORE PICKING UP AGAIN THIS EVENING. WITH THE STRENGTHENING
SUBSIDENCE INVERSION...WILL KEEP THE AIRMET GOING FOR MODERATE
LOW-LEVEL TURBULENCE. WINDS ARE EXPECTED TO STRENGTHEN FURTHER LATE
SATURDAY AS A NEW HIGH BUILDS NORTH OF THE STATE...WHICH WILL
FURTHER INCREASE THE POTENTIAL FOR LOW-LEVEL TURBULENCE THROUGH AT
LEAST MONDAY.


&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ IS IN EFFECT FOR THE TYPICAL WINDY
ZONES AROUND THE BIG ISLAND AND MAUI COUNTY...PLUS THE KAIWI
CHANNEL THROUGH SUNDAY. THE SCA IS A RESULT OF STRONG TRADE WINDS
ACCELERATING AROUND THE ISLAND TERRAIN. GIVEN THE TRADE WINDS ARE
ANTICIPATED TO REMAIN STRONG INTO TUESDAY...THE SCA WILL LIKELY BE
EXTENDED DURING THE WEEKEND. THERE IS ALSO THE POSSIBILITY WINDS COULD
BECOME STRONG ENOUGH TO EXPAND THE COVERAGE AREA INTO MORE COASTAL
MARINE ZONES...PARTICULARLY SATURDAY NIGHT THROUGH MONDAY. CHOPPY SURF IS
EXPECTED BE ALONG EAST FACING SHORES AS WIND SPEEDS REMAIN ELEVATED.

THE CURRENT NORTHWEST SWELL WILL CONTINUE TO DECLINE THROUGH
SATURDAY. MINOR REINFORCEMENT SWELLS ARE EXPECTED ON SUNDAY AND
TUESDAY NIGHT. ONLY SMALL SURF IS EXPECTED ALONG SOUTH FACING
SHORES THROUGH THE WEEKEND...THEN BUILDING TO MODERATE SURF
HEIGHTS ON TUESDAY. THE SOUTH SWELL WILL GRADUALLY DECLINE
THROUGH THE REST OF NEXT WEEK.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR KAIWI CHANNEL-
MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND
LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.


&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...BRAVENDER




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