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Hawaiian Islands Synoptic Discussion and Guidance

372
FXHW60 PHFO 020630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SUN MAY 1 2016

.SYNOPSIS...
MODERATE TO LOCALLY BREEZY TRADE WINDS WILL PERSIST ACROSS THE
ISLANDS THROUGH WEDNESDAY. LOW CLOUDS AND SHOWERS WILL FAVOR
WINDWARD AND MAUKA SECTIONS...WITH AN INCREASE IN SHOWER ACTIVITY
EXPECTED TUESDAY NIGHT AND WEDNESDAY AS MOISTURE FROM THE REMNANTS
OF AN OLD FRONT MOVES THROUGH THE AREA. A LATE SEASON FRONT IS
EXPECTED TO APPROACH THE ISLANDS THURSDAY...CAUSING OUR WINDS TO
WEAKEN AND VEER TO THE SOUTHEAST. THE FRONT MAY STALL NEAR KAUAI
LATE THIS WEEK...THEN DISSIPATE WITH TRADE WINDS RETURNING DURING
THE WEEKEND.

&&

.DISCUSSION...
TRANQUIL TRADE WIND WEATHER PREVAILS ACROSS HAWAII ON THIS SUNDAY
EVENING. WIDELY SCATTERED LIGHT SHOWERS ARE MOVING QUICKLY FROM
EAST TO WEST WITHIN THE BRISK TRADE FLOW...WITH A FEW GAUGES
REPORTING LIGHT RAINFALL AMOUNTS OF ONE QUARTER INCH OR LESS
DURING THE PAST SIX HOURS. SURFACE ANALYSIS DEPICTS A 1031 MB HIGH
CENTERED ABOUT 1000 MILES NORTH OF THE STATE. AN EAST TO WEST
ORIENTED BAND OF LOW CLOUDS...ASSOCIATED WITH A WEAKENING
FRONT...IS LOCATED ABOUT 400 MILES NORTH OF OAHU. A DRY AND STABLE
AIRMASS PREVAILS OVER THE REGION...WITH THE 00Z SOUNDINGS SHOWING
STRONG INVERSIONS BASED BETWEEN 6000 AND 7000 FEET...AND PWATS
BELOW ONE INCH. ALOFT...A STRONG MID/UPPER LEVEL ANTICYCLONE IS
CENTERED JUST EAST OF MIDWAY...WITH A RIDGE EXTENDING ESE OVER THE
ISLANDS.

OVERNIGHT...THE BEST RAIN CHANCES APPEAR TO BE OVER WINDWARD
OAHU AND KAUAI...WITH A SMALL AREA OF SHOWERY CUMULUS POISED
JUST TO THE EAST/NORTHEAST OF THOSE ISLANDS. ELSEWHERE...CLOUDS
AND SHOWERS MAY INCREASE SOMEWHAT LATE TONIGHT OVER WINDWARD AREAS
AS OFTEN OCCURS...BUT EXPECT JUST SCATTERED AND LIGHT RAINFALL
AMOUNTS. THE EXISTING FORECAST APPEARS TO BE ON TRACK...AND NO
UPDATES ARE PLANNED FOR THIS EVENING.

BREEZY AND GENERALLY DRY TRADE WIND WEATHER IS EXPECTED TO
CONTINUE THROUGH TUESDAY MORNING. SFC HIGH PRESSURE FAR TO OUR
NORTH WILL SHIFT SLOWLY EASTWARD...MAINTAINING MODERATE TO FRESH
TRADE WINDS LOCALLY...WITH CLOUDS AND PASSING SHOWERS FOCUSED OVER
WINDWARD AREAS. A WETTER TRADE WIND PATTERN SHOULD DEVELOP LATE
TUESDAY THROUGH WEDNESDAY...AS ENHANCED MOISTURE ASSOCIATED WITH
THE REMNANTS OF AN OLD FRONT MOVES THROUGH WITHIN THE TRADE WIND
FLOW. EXPECT SHOWERS TO BECOME MORE FREQUENT AND WIDESPREAD OVER
WINDWARD AREAS ESPECIALLY TUE NIGHT AND WED MORNING...WITH
SCATTERED SHOWERS SPILLING OVER INTO MANY LEEWARD AREAS OF THE
SMALLER ISLANDS.

FORECAST UNCERTAINTY INCREASES FOR THURSDAY INTO THE WEEKEND...
WHEN MODELS SHOW A LATE-SEASON FRONT APPROACHING THE ISLANDS
FROM THE NORTHWEST. THE 02/00Z GFS RUN HAS BACKED OFF SOMEWHAT
WITH THIS FEATURE...WITH THE UPPER TROUGH STAYING TO OUR NORTH AND
THE SOUTHERN END OF THE WEAKENING FRONT HANGING UP NEAR KAUAI
BEFORE EVENTUALLY DISSIPATING. THIS IS MORE IN LINE WITH THE
EXISTING OFFICIAL FORECAST. WILL AWAIT THE NEW ECMWF RUN...BUT AT
THIS POINT WE ARE LOOKING FOR DISRUPTED TRADE WINDS WITH LOCAL
SEABREEZE DEVELOPMENT THURSDAY AND FRIDAY...FOLLOWED BY A RETURN
OF TRADE WINDS DURING THE WEEKEND. SHOWERS SHOULD BE A BIT MORE
PREVALENT...ESPECIALLY FOR LEEWARD AREAS THURSDAY/FRIDAY...DUE TO
ENHANCED MOISTURE LINGERING AROUND THE STATE AND SLIGHT
INSTABILITY ALOFT.

&&

.AVIATION...
HIGH PRESSURE NORTH OF THE STATE WILL KEEP A MODERATE TO BREEZY
TRADE WIND FLOW IN PLACE THROUGH MONDAY...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 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 MONDAY.

AIRMET SIERRA MAY BE NEEDED FOR PORTIONS OF THE ISLANDS LATER
TONIGHT DUE TO MOUNTAIN OBSCURATION.

&&

.MARINE...
THE SUNDAY MORNING ASCAT PASS AND RECENT MESONET DATA SUGGEST THAT
SMALL CRAFT ADVISORY /SCA/ CONDITIONS ARE LIKELY ONGOING ACROSS
THE TYPICALLY WINDY WATERS AROUND MAUI COUNTY AND THE BIG
ISLAND...AND A SCA IS POSTED FOR THOSE WATERS THROUGH TUESDAY. SCA
CONDITIONS WILL LIKELY CONTINUE FOR THESE WATERS THROUGH WEDNESDAY.
HIGH-RES MODELS SUGGEST THAT SCA CONDITIONS COULD OCCUR IN SOME OF
THE OTHER CHANNELS MONDAY AND MONDAY NIGHT. WILL TAKE A LOOK AT
THE OVERNIGHT ASCAT DATA AND THE LATEST MODELS BEFORE DECIDING
WHETHER TO EXPAND THE SCA COVERAGE AREA.

A SMALL NORTHWEST SWELL WILL SLOWLY DECLINE THROUGH TUESDAY. A
NEW SMALL LONGER PERIOD WEST-NORTHWEST SWELL IS EXPECTED TO ARRIVE
WEDNESDAY AND LINGER THROUGH SATURDAY. ELSEWHERE...EXPECT A
NOTICEABLE BUMP IN SURF HEIGHTS ALONG SOUTH FACING SHORES FOR
MONDAY THROUGH TUESDAY. ANOTHER SLIGHTLY LARGER SOUTH SWELL IS
FORECAST TO ARRIVE FRIDAY AND CONTINUE THROUGH THE WEEKEND. TRADE
WINDS WILL PRODUCE CHOPPY SHORT PERIOD SURF ALONG EAST FACING
SHORES THROUGH MIDWEEK.

&&

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

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...JELSEMA

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office



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