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Hawaiian Islands Synoptic Discussion and Guidance

782
FXHW60 PHFO 180829 CCA
AFDHFO

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST THU APR 17 2014

.SYNOPSIS...
TRADE WIND WEATHER WILL CONTINUE ACROSS THE MAIN HAWAIIAN ISLANDS
THROUGH NEXT WEEK AS HIGH PRESSURE DOMINATES TO OUR 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...
AREA OF SURFACE HIGH PRESSURE PREVAILING NORTH OF THE ISLANDS AND
WILL MAINTAIN TRADE WINDS TO THE STATE. THE PRESSURE GRADIENT
BETWEEN THIS HIGH PRESSURE AREA AND EQUATORIAL LOW PRESSURE WILL
REMAIN HIGH ENOUGH TO SUPPORT MODERATE TO LOCALLY STRONG TRADE
WINDS OVER THE AREA THROUGH THE WEEKEND. LATEST SATELLITE IMAGERY
AS WELL AS RADAR DATA REVEALED AN AREA OF LOW CLOUDS PASSING MAINLY
OVER OAHU THIS EVENING...BRINGING SOME SHOWERS. THERE ARE STILL MORE
LOW CLOUDS FURTHER UPSTREAM EAST OF THE ISLANDS...AND THESE CLOUDS
WILL EVENTUALLY TRACK ACROSS THE STATE LATER TONIGHT INTO EARLY
FRIDAY. THERE IS ALSO A SLOW-MOVING UPPER LEVEL TROUGH IN THE
ISLAND VICINITY. THIS TROUGH IS BRINGING HIGH CLOUDS FROM THE
CONVECTION FAR SOUTHEAST OF THE ISLANDS IN THE TROPICS...KEEPING
SKIES A LITTLE MORE CLOUDY OVER THE EASTERN ISLANDS. THE PRESENT OF
THIS UPPER LEVEL TROUGH IS ALSO KEEPING AIR MASS SLIGHT UNSTABLE IN
THE ISLAND VICINITY...WHICH IS FAVORABLE FOR WETTING RAIN TO
DEVELOP. IN ALL...TRADE WIND WEATHER WILL PREVAIL OVER THE ISLANDS
FOR THE EARLY PART OF THE WEEKEND...WITH LOCALLY STRONGER WINDS
BLOWING AT TIMES. PASSING LOW CLOUDS AND SHOWERS WILL AFFECT MAINLY
WINDWARD AND MOUNTAIN AREAS...THOUGH WINDS ARE STRONG ENOUGH TO FOR
SOME SHOWERS REACHING THE LEE AREAS OF THE SMALLER ISLANDS.

MODELS SHOW 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 TO TRADE WINDS ACROSS THE
AREA FROM SUNDAY ONWARD AS THE SURFACE GRADIENT TIGHTENS FURTHER.
THE UPPER TROUGH MAY PERSIST IN THE ISLAND VICINITY THROUGH THE
MIDDLE OF NEXT WEEK...AND MAY KEEP THE AIR MASS IN THE ISLAND
SLIGHTLY UNSTABLE THUS FAVORING SHOWER DEVELOPMENT.

&&

.AVIATION...
TRADE WINDS WILL REMAIN STRONG ENOUGH AROUND THE ISLANDS TO WARRANT
THE CONTINUATION OF THE AIRMET FOR LOW-LEVEL TURBULENCE.

AN AIRMET IS ALSO IN EFFECT FOR MODERATE UPPER LEVEL TURBULENCE AS
AN UPPER TROUGH PERSISTS ACROSS THE STATE...BRINGING STRONG WIND
SHEAR AND DEFORMATION OVER THE AREA. MODEL GUIDANCE INDICATE THE
POTENTIAL FOR CLEAR-AIR TURBULENCE IN THE AREA CONTINUES THROUGH
EARLY FRIDAY MORNING.

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

&&

.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 FRESH TRADE WINDS PERSIST.

LATEST READINGS FROM THE OFFSHORE BUOY NORTH OF OAHU INDICATED THE
SLIGHT NORTHWEST SWELL MAY HAVE PEAKED THIS EVENING. A NEW SMALL
NORTHWEST SWELL IS EXPECTED OVER THE WEEKEND. TRADE WIND SWELL WILL
REMAIN ELEVATED SOMEWHAT AS THE MODERATE TO FRESH TRADE WINDS
PERSIST.

&&

.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