Funnel Cloud in Hawaii, April 4, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED APR 4 2012

.SYNOPSIS...
EXPECT LIGHT EAST SOUTHEAST WINDS TO CONTINUE WITH LOCAL SEA BREEZES
DEVELOPING AGAIN THIS AFTERNOON. LOW CLOUDS AND ISOLATED SHOWERS
WILL OCCUR PRIMARILY ALONG SOUTHEAST FACING SLOPES THIS MORNING...
AND MAINLY OVER INTERIOR AND LEEWARD SECTIONS OF THE STATE THIS
AFTERNOON. MODERATE TRADE WINDS WILL RETURN THURSDAY...WITH STRONGER
TRADES EXPECTED THIS WEEKEND. THE RETURN OF THE TRADES WILL
GRADUALLY BRING A MORE TYPICAL TRADE WIND WEATHER PATTERN DURING THE
SECOND HALF OF THE WEEK.

&&

.DISCUSSION...
A SOMEWHAT COMPLICATED WEATHER PATTERN CONTINUES AROUND THE HAWAIIAN
ISLANDS EARLY THIS MORNING. FOR EXAMPLE...A BAND OF BROKEN TO
OVERCAST LOW CLOUDS AND SHOWERS ASSOCIATED WITH A SURFACE FRONT IS
LOCATED SLIGHTLY MORE THAN 400 MILES NORTH OF HONOLULU. AS A RESULT
OF THIS LOWER PRESSURE TO THE NORTH AND NORTHWEST OF THE ISLANDS...
THE PRESSURE GRADIENT REMAINS RELAXED ACROSS THE REGION. THIS IS
RESULTING IN LIGHT EAST SOUTHEAST SURFACE WINDS...WHICH IS ALLOWING
THE DEVELOPMENT OF ALTERNATING LOCAL NIGHTTIME LAND BREEZE AND
AFTERNOON SEA BREEZE CIRCULATIONS OVER THE ISLANDS. PATCHES OF
VOLCANIC HAZE ARE ALSO LIKELY BEING CARRIED UP OVER THE WESTERN END
OF THE STATE FROM SOURCES ON THE BIG ISLAND.

ANOTHER FEATURE WHICH CONTINUES TO COMPLICATE THE WEATHER ACROSS THE
ISLANDS IS AN UPPER LEVEL TROUGH FAR WEST OF KAUAI. THERE IS A LARGE
AREA OF BROKEN TO OVERCAST LAYERED CLOUDS WITH EMBEDDED
THUNDERSTORMS ASSOCIATED WITH THIS TROUGH. SO THE MAIN INFLUENCE
THIS SYSTEM IS HAVING ON ISLAND WEATHER HAS BEEN THE TRANSPORT OF
CIRRUS CLOUDS...WHICH ARE OCCASIONALLY STREAMING ACROSS OUR SKIES.
THE EARLY MORNING ATMOSPHERIC SOUNDING FROM LIHUE HAS ALSO BECOME
SLIGHTLY MORE UNSTABLE...DUE TO THE COOLER TEMPERATURES AND
DIVERGENT FLOW ALOFT. HOWEVER...THERE IS STILL A FAIRLY SIGNIFICANT
LOW-LEVEL INVERSION BETWEEN 6 AND 7 THOUSAND FEET...WHICH IS KEEPING
KAUAI FAIRLY DRY THIS MORNING.

THE LOCAL LAND BREEZES CLEARED LOW CLOUDS AND SHOWERS AWAY FROM SOME
OF THE ISLANDS OVERNIGHT. HOWEVER...SHOWER BEARING CLOUDS CONTINUE
TO AFFECT PARTS OF EAST MAUI AND THE BIG ISLAND...AS WELL AS THE
KOOLAU MOUNTAIN RANGE ON OAHU. ADDITIONAL SHOWERS CONTINUE TO
DEVELOP JUST SOUTH OF OAHU...BUT MOST OF THESE HAVE BEEN DISSIPATING
WHEN THEY CROSS THE SOUTHERN BEACHES OF THAT ISLAND. IN ADDITION TO
THE CLOUDS AND SHOWERS AFFECTING PARTS OF THE STATE THIS MORNING...
EXPECT THE CLOUD BUILDUPS AND SOME SHOWERS TO DEVELOP AGAIN OVER
LEEWARD AND INTERIOR SECTIONS OF MOST OF THE ISLANDS THIS AFTERNOON.
DUE TO THE POTENTIAL FOR SOME INCREASED VERTICAL DEVELOPMENT OF THE
CLOUDS IN THE SLIGHTLY UNSTABLE AIR MASS OVER THE EXTREME WESTERN
END OF THE MAIN HAWAIIAN ISLANDS...HAVE INCLUDED THE POSSIBILITY OF
LOCALLY HEAVY RAINFALL OCCURRING OVER KAUAI AND THE SURROUNDING
COASTAL WATERS THIS AFTERNOON.

BY THURSDAY...SURFACE HIGH PRESSURE BUILDING FAR NORTHWEST OF THE
AREA WILL BEGIN TO TIGHTEN THE PRESSURE GRADIENT ACROSS THE
STATE...WHICH WILL ALLOW MODERATE TRADE WINDS TO RETURN. AS THIS
HIGH CONTINUES MOVING EASTWARD TO A POSITION FAR NORTH OF THE ALOHA
STATE...THE TRADES WILL GRADUALLY STRENGTHEN FRIDAY AND SATURDAY.

AS WAS NOTED EARLIER...THE FORECAST STILL HAS SOME COMPLICATED
ASPECTS. FOR EXAMPLE...THE GLOBAL MODELS AGREE THAT A CLOSED UPPER
LEVEL LOW WILL DEVELOP FAR WEST OF KAUAI BY TONIGHT. AN UPPER LEVEL
TROUGH WILL EXTEND EAST FROM THIS LOW OVER THE STATE. A SURFACE
LOW...WHICH WILL BE A REFLECTION OF THE UPPER LEVEL LOW...IS ALSO
FORECAST TO FORM TO OUR WEST. THE PRESENCE OF THE DEEPENING SURFACE
LOW WILL RESULT IN ORGANIZED DEEP CONVECTION. HOWEVER...THE
WIDESPREAD HEAVY RAINFALL ASSOCIATED WITH THIS LOW SHOULD REMAIN
WEST OF THE ISLANDS.

EVEN THOUGH THE UPPER LEVEL LOW IS EXPECTED TO MOVE SLOWLY
WESTWARD...THE TROUGH AND ITS COOL TEMPERATURES ALOFT ARE EXPECTED
TO REMAIN IN THE VICINITY OF THE ISLANDS. THE CURRENT FORECAST IS
FOR LIGHT TO MODERATE TRADE SHOWERS TOMORROW...BUT THERE IS A SLIGHT
CHANCE SOME LOCALLY HEAVY SHOWERS MAY DEVELOP DUE TO THE PRESENCE OF
THIS UPPER LEVEL SYSTEM.

THE LATEST OUTPUT FROM THE FORECAST MODELS INDICATES THE SURFACE
HIGH WILL REMAIN FAR NORTH OF THE ALOHA STATE INTO NEXT WEEK. A
DYING FRONT OR A SHEAR LINE IS ALSO DEPICTED IN THE FORECAST MODELS
APPROACHING THE ISLANDS FROM THE NORTH BY EARLY SUNDAY. THIS SHEAR
LINE APPEARS POISED TO PUSH DOWN ACROSS THE STATE LATE SUNDAY AND
MONDAY WITH AN INCREASE IN TRADE WIND SPEEDS AS IT PASSES. THESE
STRONGER TRADES WILL LIKELY PERSIST INTO EARLY NEXT WEEK...WITH A
RATHER TYPICAL TRADE WIND WEATHER DISTRIBUTION OF LOW CLOUDS AND
SHOWERS.

&&

.AVIATION...
LOW CLOUDS AND ISOLATED SHOWERS MAY BRING BRIEF MVFR CONDITIONS TO
SOUTHEAST FACING SLOPES THIS MORNING...AND OVER SOME LEEWARD AND
INTERIOR SECTIONS OF THE ISLANDS THIS AFTERNOON.

&&

.MARINE...
THE MODERATE-SIZED SURF PRODUCED BY THE CURRENT NORTHWEST SWELL
ALONG MOST NORTH AND WEST FACING SHORES WILL GRADUALLY LOWER AS THE
SWELL SHIFTS TO A MORE NORTHERLY DIRECTION LATER TODAY AND TONIGHT.
ANOTHER SMALL NORTHWEST SWELL IS EXPECTED TO ARRIVE FRIDAY
NIGHT...WITH SURF PEAKING ALONG MOST NORTH AND WEST FACING SHORES ON
SATURDAY BEFORE THIS SWELL GRADUALLY SUBSIDES SUNDAY. SHORT PERIOD
WIND WAVES WILL BUILD ALONG EAST FACING SHORES LATER THIS WEEK WHEN
THE TRADES INCREASE. A SMALL...BUT LONG PERIOD...SOUTH SWELL
ARRIVING FRIDAY WILL LIKELY PRODUCE A NOTICEABLE BUMP IN SURF
HEIGHTS ALONG SOUTH FACING SHORES THIS WEEKEND.

THE RELATIVELY LIGHT WIND REGIME AND LACK OF ANY LARGE SWELLS WILL
KEEP CONDITIONS OVER ALL OF THE HAWAIIAN COASTAL WATERS BELOW THE
SMALL CRAFT ADVISORY /SCA/ CRITERIA AT LEAST THROUGH FRIDAY.
STRENGTHENING TRADE WINDS AND ROUGHER SEAS WILL LIKELY REQUIRE A SCA
OVER THE TYPICALLY WINDY WATERS ADJACENT TO MAUI COUNTY AND THE BIG
ISLAND ON SATURDAY. WITH THE TRADES EXPECTED TO BECOME STRONGER AS
THE SHEAR LINE MOVES DOWN THE ISLAND CHAIN...THE SCA MAY SPREAD TO
MOST OF THE REMAINING COASTAL WATERS STARTING SUNDAY OR MONDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

HOUSTON