Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 290131
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
331 PM HST THU APR 28 2016

.SYNOPSIS...
A STRONG RIDGE NORTH OF THE AREA WILL KEEP TRADE WINDS LOCALLY
BREEZY. A SLIGHT WEAKENING IS POSSIBLE ON FRIDAY AND SATURDAY AS
A FRONT PASSES NORTH OF THE STATE...THEN A NEW HIGH WILL BUILD IN
TO OUR NORTH EARLY NEXT WEEK. THE TRADES WILL FOCUS SHOWERS
PRIMARILY OVER WINDWARD SLOPES. SOME SHOWERS WILL SPREAD LEEWARD
OVER THE SMALLER ISLANDS...MAINLY NIGHTS AND MORNINGS. AFTERNOON
SHOWERS ARE EXPECTED OVER THE LEE SLOPES OF THE BIG ISLAND.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL RIDGE OVER/NORTHEAST OF
THE STATE. AT THE SURFACE...HIGH PRESSURE IS LOCATED NORTHEAST OF
THE STATE...WITH A RIDGE PASSING SEVERAL HUNDRED MILES TO OUR
NORTH. 00Z SOUNDINGS FROM LIHUE AND HILO SHOW INVERSIONS OF
7-9KFT. PRECIPITABLE WATERS ARE 1.0 AND 1.2 INCHES RESPECTIVELY...
WHICH IS NEAR AVERAGE FOR APRIL. EARLY AFTERNOON MIMIC TOTAL
PRECIPITABLE WATER IMAGERY SHOWS A POCKET OF MOISTURE WITH VALUES
NEAR 1.3 INCHES NORTH OF KAUAI...AND DRIER AIR WITH VALUES OF 1
INCH OR LESS EXTENDING SEVERAL HUNDRED MILES EAST OF THE STATE.

IN THE LARGE SCALE...AN UPPER LEVEL TROUGH AND COLD FRONT WILL
PASS WELL NORTH OF THE STATE THIS WEEKEND. WHILE THE FRONT WILL
NOT REACH OUR LATITUDE...IT WILL WEAKEN AND DISPLACE THE HIGH TO
THE NORTHEAST AND LEAD TO A SUBTLE DROP IN WIND SPEEDS OVER THE
NEXT COUPLE DAYS /LOCALLY BREEZY VERSUS THE CURRENT MORE
WIDESPREAD BREEZY/. FORECAST SOUNDINGS AND CROSS SECTIONS SHOW
ONLY MINOR FLUCTUATIONS IN INVERSION HEIGHT/MOISTURE DEPTH...
LEADING TO A RELATIVELY CONSISTENT AND TYPICAL TRADE WIND PATTERN
FOR CLOUDS/SHOWERS THROUGH THE WEEKEND.

AS THE FRONT AND PARENT LOW PULL FARTHER AWAY FROM THE STATE...A
NEW HIGH WILL BUILD IN TO OUR NORTH LATE IN THE WEEKEND...BRINGING
ANOTHER SURGE IN TRADE WIND SPEEDS. MOISTURE LEFT BEHIND BY THE
FRONT WILL GET PICKED UP BY THE TRADES AND ENHANCE SHOWERS ACROSS
THE ISLANDS BY THE MIDDLE OF NEXT WEEK. TIMING IS STILL
UNCERTAIN...WITH EXTENDED MODELS SHOWING QUITE A SPREAD FROM AS
EARLY AS TUESDAY IN THE ECMWF TO AS LATE AS THURSDAY IN THE GFS.
IT DEPENDS ON EXACTLY HOW THE OLD FRONTAL MOISTURE INTERACTS WITH
THE HIGH AND HOW QUICKLY IT MOVES SOUTH. RIGHT NOW AM LEANING
TOWARD THE SLOWER GFS AS IT SEEMS AS THOUGH IT SHOULD TAKE LONGER
FOR THE MOISTURE TO WORK DOWN TO OUR LATITUDE...BUT IT IS TOO
EARLY TO RELIABLY DETERMINE WHICH IS MORE LIKELY AT THIS POINT.
THEREFORE WILL KEEP SIMILAR CLIMATOLOGICAL POPS THROUGH MUCH OF
NEXT WEEK.

&&

.AVIATION...
MODERATE TO FRESH TRADE WINDS WILL FOCUS CLOUDS AND LIGHT SHOWERS
OVER THE WINDWARD AND MAUKA AREAS. AIRMET TANGO REMAINS IN EFFECT
FOR TEMPO MODERATE LOW LEVEL TURB OVER AND IMMEDIATELY S THROUGH W
OF THE MOUNTAINS DUE TO THE TRADES. THE WILL REMAIN UP THROUGH
TONIGHT AND POSSIBLY FRIDAY AS WELL.

TEMPO MVFR CIGS AND MTN OBSC WILL BE POSSIBLE LATE TONIGHT FOR SOME
OF THE WINDWARD AREAS...WHICH MAY PROMPT AN AIRMET SIERRA ISSUANCE.

&&

.MARINE...
THE MORNING ASCAT PASS ONLY CLIPPED THE WESTERN HALF OF THE
STATE...AND MISSED THE AREA WHERE THE SMALL CRAFT ADVISORY IS
CURRENTLY IN EFFECT. HOWEVER...THE LARGE AREA OF 20 KNOT WINDS
AROUND OAHU DOES VALIDATE THE STRONGER MODEL SOLUTIONS...WHICH
CONTINUE TO SHOW 25 KNOTS THROUGH THE TYPICALLY WINDIER AREAS. THE
CURRENT ADVISORY RUNS THROUGH TONIGHT...WITH THE IDEA THAT THE
WEAKENING GRADIENT WILL CAUSE WINDS TO DROP BELOW 25 KNOTS. THE
DECREASE IN WINDS IS LESS PRONOUNCED THAN EXPECTED BEFORE...AND WE
WILL BE BORDERLINE FOR SMALL CRAFT THROUGH THE WEEKEND. WILL HOLD
OFF ON ADJUSTING THE ADVISORY FOR NOW SO WE CAN GET A LOOK AT THE
EVENING ASCAT PASS TO SEE HOW THE TREND IN SPEEDS IS PROGRESSING.

THE MOKAPU AND HILO BUOYS SHOW SEAS OF 8-9 FEET DUE MAINLY TO
TRADE SWELL /MAINLY EAST-NORTHEAST THOUGH THE HILO BUOY IS
REPORTING MORE OF A EAST-SOUTHEAST DIRECTION/. THIS SWELL SHOULD
GRADUALLY DECREASE OVER THE NEXT COUPLE DAYS AS THE HIGH TO THE
NORTHEAST WEAKENS...THEN PICK BACK UP EARLY NEXT WEEK AS THE NEXT
HIGH BUILDS NORTH OF THE AREA. SMALL SWELLS FROM THE NORTHWEST AND
SOUTH ARE ALSO IN STORE THIS WEEK. SURF ALONG SOUTH FACING SHORES
MAY RISE EARLY NEXT WEEK AS A SWELL FROM EAST OF NEW ZEALAND
REACHES THE ISLANDS.

&&

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

&&

$$

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


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