Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 282005
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1005 AM HST THU APR 28 2016

.SYNOPSIS...
A STRONG RIDGE NORTH OF THE AREA WILL MAINTAIN LOCALLY BREEZY
TRADE WINDS THROUGH TONIGHT. THE TRADES WILL WEAKEN A BIT FRIDAY
AND SATURDAY AS A FRONT PASSES NORTH OF THE STATE...THEN
STRENGTHEN EARLY NEXT WEEK AS A NEW HIGH BUILD IN TO OUR NORTH.
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. 12Z SOUNDINGS FROM LIHUE AND HILO SHOW INVERSIONS OF
7-8KFT. PRECIPITABLE WATERS ARE 1.1-1.2 INCHES...WHICH IS JUST
ABOUT AVERAGE FOR APRIL. EARLY MORNING MIMIC TOTAL PRECIPITABLE
WATER IMAGERY SHOWS A POCKET OF MOISTURE WITH VALUES NEAR 1.2
INCHES AROUND THE SMALLER ISLANDS...AND DRIER AIR WITH VALUES
BELOW 1 INCH EXTENDING SEVERAL HUNDRED MILES UPSTREAM OF THE BIG
ISLAND.

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 /MODERATE VERSUS THE CURRENT 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 SHOWERS OVER THE
WINDWARD AND MAUKA AREAS.  ISOL MVFR CIGS/MTN OBSC WILL BE POSSIBLE
THROUGH THE MORNING...HOWEVER DECREASING CLOUD AND SHOWER COVERAGE
IS EXPECTED THROUGH THE REST OF TODAY AND NO AIRMET IS IN EFFECT FOR
TEMPO MTN OBSC.

AIRMET TANGO REMAINS IN EFFECT FOR TEMPO MODERATE LOW LEVEL TURB
OVER AND IMMEDIATELY S THROUGH W OF THE MOUNTAINS DUE TO THE BREEZY
TRADES. AIRMET TANGO WILL REMAIN UP THROUGH THE DAY AND POSSIBLY
ON FRIDAY AS WELL.

&&

.MARINE...
THE OVERNIGHT ASCAT PASS MISSED THE BIG ISLAND...BUT SHOWED A
LARGE AREA OF 25+ KNOT WINDS DOWNSTREAM OF BOTH THE ALENUIHAHA
CHANNEL AND SOUTH POINT. THE CURRENT SMALL CRAFT ADVISORY RUNS
THROUGH TONIGHT. AS THE HIGH WEAKENS FRIDAY/SATURDAY...NAM/GFS/ECMWF
AND THE HIGH RESOLUTION WRF FROM UH SHOW WINDS DROPPING ON FRIDAY
AND REMAINING BORDERLINE FOR 25 KNOTS...WHILE THE WRF-NMM/ARW AND
NAM NEST KEEP WINDS STRONGER THROUGH THE CHANNELS.

SMALL SWELLS FROM THE NORTHWEST AND SOUTH ARE IN STORE THIS
WEEK...WHILE MODERATE...SHORT-PERIOD TRADE WIND SWELL CONTINUES.
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.

&&

$$

PUBLIC/MARINE...BRAVENDER
AVIATION...FOSTER



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