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Hawaiian Islands Synoptic Discussion and Guidance

563
FXHW60 PHFO 181354
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI APR 18 2014

.SYNOPSIS...
TRADE WIND WEATHER WILL CONTINUE ACROSS THE MAIN HAWAIIAN ISLANDS
THROUGH NEXT WEEK AS HIGH PRESSURE DOMINATES TO THE NORTH.
CLOUDS AND SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS...WHILE
LEEWARD BIG ISLAND WILL SEE MORE CLOUDS AND SHOWERS DURING THE
AFTERNOON AND EVENING HOURS.

&&

.DISCUSSION...
QUITE A BIT OF SHOWERS AFFECTING THE WINDWARD AREAS OF THE ISLANDS
EARLY THIS MORNING...AS REVEALED BY RADAR DATA. LATEST RAINFALL
REPORT INDICATED MEASURABLE AMOUNTS ON THE WINDWARD GAGES...THOUGH
THE NUMBERS ARE NOWHERE HIGH ENOUGH TO BE A CONCERN. THESE SHOWERS
ARE MOVING RATHER QUICKLY UNDER THE MODERATE TRADE WINDS...THUS
LIMITING THE ACCUMULATIONS. EARLY MORNING SOUNDINGS FROM LIHUE AND
HILO INDICATE LOW LEVEL MOISTURE IS NOW EXTENDING TO 8 TO 9 THOUSAND
FEET...WHILE THE AIR MASS REMAINS SLIGHTLY UNSTABLE. THEREFORE
ATMOSPHERIC CONDITIONS REMAIN FAVORABLE FOR WETTING RAIN TO DEVELOP.
AREA OF SURFACE HIGH PRESSURE PREVAILING NORTH OF THE ISLANDS WILL
MAINTAIN TRADE WINDS TO THE STATE TODAY. THE SURFACE PRESSURE
GRADIENT ACROSS THE AREA WILL REMAIN HIGH ENOUGH TO SUPPORT MODERATE
TO LOCALLY STRONG TRADE WINDS OVER THE ISLANDS. A SLOW-MOVING UPPER
LEVEL TROUGH CONTINUES IN THE ISLAND VICINITY. THIS TROUGH IS
DRAWING HIGH CLOUDS FROM THE CONVECTION FAR SOUTHEAST OF THE STATE.
AND THESE HIGH CLOUDS ARE KEEPING SKIES A LITTLE MORE CLOUDY OVER
THE STATE. THE PRESENT OF THIS UPPER LEVEL TROUGH IS ALSO THE REASON
WHY THE AIR MASS REMAINS SLIGHT UNSTABLE IN THE ISLAND VICINITY.

NOT MUCH CHANGES ARE EXPECTED IN THE OVERALL WEATHER PATTERN IN THE
COMING DAYS. THEREFORE TRADE WIND WEATHER WILL PREVAIL OVER THE
ISLANDS THROUGH THE WEEKEND INTO NEXT WEEK. PASSING LOW CLOUDS AND
SHOWERS WILL AFFECT MAINLY WINDWARD AND MOUNTAIN AREAS...THOUGH
WINDS ARE STRONG ENOUGH TO BRING SOME SHOWERS TO THE LEE AREAS OF
THE SMALLER ISLANDS. LATEST MODEL GUIDANCE STILL INDICATES A
STRONGER HIGH PRESSURE WILL BUILD ALONG THE RIDGE NORTHWEST OF THE
ISLANDS OVER THE WEEKEND...THEN PUSH EASTWARD EARLY NEXT WEEK. THIS
MAY RESULT A SLIGHT BOOST OF TRADE WINDS ACROSS THE STATE SUNDAY AND
MONDAY. THE UPPER LEVEL TROUGH MAY ALSO PERSIST IN THE ISLAND
VICINITY THROUGH EARLY NEXT WEEK...AND MAY KEEP THE AIR MASS IN THE
ISLAND VICINITY SLIGHTLY UNSTABLE...WHICH IS FAVORABLE FOR SHOWERS
TO DEVELOP.

&&

.AVIATION...
TRADE WINDS WILL REMAIN STRONG ENOUGH IN THE ISLAND VICINITY TO
WARRANT THE CONTINUATION OF THE AIRMET FOR LOW-LEVEL TURBULENCE
TODAY.

AN AIRMET REMAINS IN EFFECT FOR MODERATE UPPER LEVEL TURBULENCE AS
AN UPPER LEVEL TROUGH PERSISTS ACROSS THE STATE...BRINGING STRONG
WIND SHEAR AT THE UPPER LEVELS. MODEL GUIDANCE INDICATES THE
POTENTIAL FOR CLEAR-AIR TURBULENCE IN THE AREA ALOFT MAY DIMINISH
LATER TODAY.

LOW CLOUDS AND SHOWERS CARRIED BY THE TRADE WINDS WILL FOCUS
PRIMARILY ACROSS WINDWARD SECTIONS. THEREFORE CONDITIONS WILL BE
PREDOMINATELY VFR...WITH OCCASIONAL MVFR CEILINGS AND VISIBILITIES
IN SHOWERS AFFECTING MAINLY WINDWARD AND MOUNTAIN AREAS.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH SATURDAY AFTERNOON
FOR TYPICALLY WINDIER AREAS AROUND MAUI AND THE BIG ISLAND AS THE
MODERATE TO LOCALLY FRESH TRADE WINDS PERSIST.

THE CURRENT SLIGHT NORTHWEST SWELL IS ON THE DECLINE EARLY THIS
MORNING FOR THE WESTERN ISLANDS. A NEW SMALL NORTHWEST SWELL IS
EXPECTED OVER THE WEEKEND. TRADE WIND SWELL WILL REMAIN ELEVATED
SOMEWHAT DUE TO THE MODERATE TO FRESH TRADE WINDS.

&&

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

&&

$$

HUI



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