Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 011413
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
413 AM HST SUN MAY 1 2016

.SYNOPSIS...
MODERATE TO LOCALLY BREEZY TRADE WINDS ARE EXPECTED TO PERSIST
ACROSS THE ISLANDS THROUGH WEDNESDAY. LOW CLOUDS AND SHOWERS
CARRIED BY THE TRADES WILL CONTINUE TO FAVOR WINDWARD AND MAUKA
SECTIONS. THERE MAY BE AN INCREASE IN TRADE SHOWER COVERAGE LATE
TUESDAY AND WEDNESDAY. A LATE SEASON FRONT IS EXPECTED TO APPROACH
THE ISLANDS FROM THE NORTHWEST THURSDAY...WHICH MAY CAUSE OUR
WINDS TO WEAKEN AND SHIFT OUT OF THE SOUTHEAST BY THE END OF THE
NEW WORK WEEK.

&&

.DISCUSSION...
A WEAKENING FRONT IS LOCATED ABOUT 375 MILES MILES NORTH OF LIHUE.
HOWEVER...A 1031 MB SURFACE HIGH CENTERED NEAR 35N 164W...OR
ABOUT 960 MILES NORTH-NORTHWEST OF LIHUE...IS GRADUALLY BUILDING
AS IT MOVES SLOWLY TOWARD THE EAST. AS THE FRONT CONTINUES TO
WEAKEN TODAY...EXPECT ADDITIONAL TIGHTENING OF THE PRESSURE
GRADIENT ACROSS THE REGION. AS A RESULT...OUR TRADE WINDS WILL
CONTINUE TO REBOUND TO MODERATE TO LOCALLY BREEZY SPEEDS.

ALOFT...MID-TROPOSPHERIC RIDGING AND UPPER LEVEL SUBSIDENCE ARE
MAINTAINING STABLE ATMOSPHERIC CONDITIONS ACROSS THE MAIN HAWAIIAN
ISLANDS EARLY THIS MORNING. PATCHES OF LOW CLOUDS AND LIGHT
SHOWERS ARE EVIDENT IN SATELLITE IMAGERY ACROSS PARTS OF THE
STATE. THESE LOW CLOUDS AND SHOWERS ARE MAINLY AFFECTING WINDWARD
FACING SLOPES AND HIGHER TERRAIN. IN ADDITION...THE INCREASING
TRADE WINDS HAVE ALSO BEEN CARRYING BRIEF TRADE SHOWERS OVER TO
THE LEEWARD SIDES OF SOME OF THE SMALLER ISLANDS...INCLUDING
OAHU...SINCE LAST EVENING.

THE FORECAST MODELS CONTINUE TO SHOW SURFACE HIGH PRESSURE
REMAINING NORTH OR NORTHEAST OF THE REGION THROUGH THE THE FIRST
FEW DAYS OF THE NEW WORK WEEK. THE TIGHT PRESSURE GRADIENT WILL
MAINTAIN THE MODERATE TO LOCALLY BREEZY TRADE WINDS ACROSS THE
STATE. A MID-TROPOSPHERIC RIDGE WILL ALSO KEEP STABLE ATMOSPHERIC
CONDITIONS ACROSS THE ISLANDS THROUGH MID-WEEK. THEREFORE...EXPECT
THE SAME GENERAL TRADE WIND SHOWER PATTERN TO CONTINUE FOR THE
NEXT FEW DAYS. BY MID-WEEK...ENHANCED LOW LEVEL MOISTURE
ASSOCIATED WITH THE OLD FRONT IS EXPECTED TO BE TRANSPORTED INTO
THE ISLANDS BY THE TRADE WIND FLOW. THEREFORE...EXPECT INCREASING
SHOWER COVERAGE...ESPECIALLY ACROSS WINDWARD AND MAUKA SECTIONS
OF THE ISLAND CHAIN...TUESDAY NIGHT AND WEDNESDAY. THE STRONG
TRADES MAY CARRY A FEW OF THESE SHOWERS OVER TO LEEWARD SECTIONS
OF SOME OF THE SMALLER ISLANDS...ESPECIALLY AT NIGHT AND IN THE
MORNING.

THE MODEL OUTPUT SHOWS A LATE SEASON FRONT APPROACHING THE
ISLANDS FROM THE NORTHWEST THURSDAY AND FRIDAY. THE LATEST GFS AND
ECMWF MODEL RUNS APPEAR TO BRING THIS FEATURE CLOSE TO KAUAI.
HOWEVER...SINCE THERE HAVE BEEN RUN-TO-RUN VARIATIONS IN THE
MODELS...THERE ARE STILL MANY UNCERTAINTIES ABOUT THE TYPE OF
WEATHER / WINDS THAT WE MIGHT EXPECT AS THIS FEATURE APPROACHES
THE AREA. IN THE MEANTIME...THE FORECAST FOR THURSDAY AND FRIDAY
HAS BEEN ADJUSTED TO INDICATE A LIGHT EAST TO SOUTHEAST FLOW
ACROSS MOST OF THE STATE. THIS TYPE OF PATTERN WOULD SUGGEST THAT
A DIURNAL PATTERN OF AFTERNOON SEA BREEZES AND NIGHTTIME LAND
BREEZES COULD DEVELOP. IF SO...EXPECT WARM AND MUGGY CONDITIONS
TO DEVELOP AS WE HEAD INTO NEXT WEEKEND. VOLCANIC HAZE COULD ALSO
BE CARRIED UP OVER THAT SMALLER ISLANDS WITH THIS SCENARIO.

&&

.AVIATION...
HIGH PRESSURE NORTH OF THE STATE WILL KEEP A MODERATE TO BREEZY
TRADE WIND FLOW IN PLACE THROUGH TONIGHT...WITH CLOUDS AND SHOWERS
FOCUSED PRIMARILY ACROSS WINDWARD AND MAUKA AREAS. MAINLY VFR
CONDITIONS ARE EXPECTED AT THE TERMINALS...BUT BRIEF MVFR CIGS/VSBYS
MAY IMPACT PHLI OR PHTO IN PASSING SHRA.

AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION ACROSS PORTIONS
OF THE BIG ISLAND. THE AIRMET MAY NEED TO BE EXPANDED TO INCLUDE
PORTIONS OF THE OTHER ISLANDS LATER THIS MORNING. CONDITIONS ARE
EXPECTED TO IMPROVE IN ALL AREAS BY 01/20Z.

AIRMET TANGO IS IN EFFECT FOR LOW LEVEL TURBULENCE OVER AND SOUTH
THRU WEST OF THE MOUNTAINS ON ALL ISLANDS. CONDITIONS ARE EXPECTED
TO REMAIN IN PLACE THROUGH TONIGHT.

&&

.MARINE...
A SCATTEROMETER PASS OVER THE ISLANDS LAST EVENING CONFIRMED THAT
TRADE WINDS HAVE ALREADY INCREASED. THEREFORE...A SMALL CRAFT
ADVISORY /SCA/ REMAINS IN EFFECT FOR THE TYPICALLY WINDY WATERS
ADJACENT TO THE ISLANDS OF MAUI COUNTY AND THE BIG ISLAND. SCA
CONDITIONS WILL LIKELY CONTINUE FOR THESE WATERS THROUGH
WEDNESDAY. THERE MAY BE ADDITIONAL MARINE ZONES...SUCH AS THE
KAIWI CHANNEL...ADDED TO THE SCA DURING THE FEW DAYS.

A SMALL NORTHWEST SWELL WHICH ARRIVED THIS MORNING IS EXPECTED
TO PEAK LATER TODAY...THEN SLOWLY LOWER MONDAY AND TUESDAY. A NEW
SMALL LONGER PERIOD WEST-NORTHWEST SWELL IS EXPECTED ON WEDNESDAY
AND THURSDAY. ELSEWHERE...EXPECT A NOTICEABLE BUMP IN SURF HEIGHTS
ALONG SOUTH FACING SHORES DURING THE NEXT FEW DAYS. THE
STRENGTHENING TRADE WINDS WILL PRODUCE SLIGHTLY ELEVATED ROUGH
SURF CONDITIONS ALONG WINDWARD BEACHES AND REEFS ACROSS THE STATE
THROUGH MID-WEEK. HOWEVER...SURF IS EXPECTED TO REMAIN BELOW THE
HIGH SURF ADVISORY CRITERIA ALONG EAST FACING SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST MONDAY FOR MAALAEA BAY...THE
WATERS SOUTH OF THE BIG ISLAND...AND THE PAILOLO AND ALENUIHAHA
CHANNELS.

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...JELSEMA



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