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Hawaiian Islands Synoptic Discussion and Guidance

008
FXHW60 PHFO 281401
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI NOV 28 2014

.SYNOPSIS...
SURFACE HIGH PRESSURE FAR NORTH OF THE ISLANDS WILL MAINTAIN STRONG
AND GUSTY TRADE WINDS ACROSS THE STATE INTO THIS WEEKEND. LINGERING
LOW-LEVEL MOISTURE WILL CONTINUE TO GENERATE SCATTERED SHOWERS
PRIMARILY ACROSS WINDWARD SECTIONS OF THE BIG ISLAND AND MAUI.
ELSEWHERE...EXPECT BRIEF SHOWERS MAINLY OVER WINDWARD AND MAUKA
SECTIONS FOR THE NEXT FEW DAYS. TRADE WIND SPEEDS ARE FORECAST TO
DIMINISH SLIGHTLY EARLY NEXT WEEK...WITH TRADE SHOWERS REMAINING
FOCUSED MAINLY ACROSS WINDWARD FACING SLOPES AND TERRAIN.

&&

.DISCUSSION...
THE TIGHT PRESSURE GRADIENT SOUTH OF A NEARLY STATIONARY 1031 MB
SURFACE HIGH NEAR 38N 161W...OR ABOUT 1100 MILES NORTH OF
HONOLULU...IS MAINTAINING STRONG AND GUSTY TRADE WINDS ACROSS THE
MAIN HAWAIIAN ISLAND CHAIN EARLY THIS MORNING. ALOFT...A
MID-TROPOSPHERIC RIDGE JUST EAST OF THE ISLANDS IS ALSO PRODUCING
STABLE ATMOSPHERIC CONDITIONS ACROSS THE REGION. THIS IS KEEPING THE
HEIGHT OF THE TRADE WIND INVERSION RELATIVELY LOW ACROSS THE ISLAND
CHAIN. THIS LOW INVERSION IS ALSO ALLOWING LOCALLY HIGHER WIND GUSTS
TO OCCUR...ESPECIALLY IN CHANNELED AREAS IN THE VICINITY OF HIGHER
TERRAIN.

SATELLITE IMAGERY AND RADAR REFLECTIVITY DATA CONTINUE TO SHOW LOW
CLOUDS AND SCATTERED SHOWERS OVER THE WINDWARD SECTIONS OF MAUI AND
THE BIG ISLAND. ELSEWHERE...THE DRY AND STABLE ATMOSPHERIC
CONDITIONS ARE ALLOWING MAINLY LIGHT TRADE SHOWERS TO DEVELOP OVER
SOME OF THE ISLANDS WEST OF MAUI AND THE BIG ISLAND.

THE FORECAST MODELS INDICATE THE TIGHT PRESSURE GRADIENT WILL REMAIN
ACROSS THE STATE THROUGH SATURDAY AS THE SURFACE HIGH SHIFTS SLOWLY
EASTWARD. THE COVERAGE OF TRADE SHOWERS WILL REMAIN FOCUSED MAINLY
ALONG WINDWARD AND MAUKA AREAS THROUGH THE REMAINDER OF THIS
WEEKEND. THE BEST CHANCE FOR SIGNIFICANT RAINFALL TOTALS WILL REMAIN
ACROSS THE WINDWARD BIG ISLAND...WITH RAINFALL AMOUNTS EXPECTED TO
BE MEAGER ELSEWHERE.

THERE WILL LIKELY BE LITTLE CHANGE IN THE THE WEATHER PATTERN FROM
LATE THIS WEEKEND THROUGH EARLY NEXT WEEK. AS THE SURFACE HIGH FAR
NORTH OF THE STATE WEAKENS SLIGHTLY AS IT SHIFTS EASTWARD...THE
PRESSURE GRADIENT WILL START TO RELAX BEGINNING SUNDAY. THIS WILL
RESULT IN SOME GRADUAL WEAKENING OF TRADE WINDS. BY MID-WEEK...A
MODEST INCREASE IN LOW-LEVEL MOISTURE MAY OCCUR. THE FORECAST MODELS
APPEAR TO INDICATE A MID-TROPOSPHERIC TROUGH MAY APPROACH THE STATE
FROM THE WEST NEXT WEDNESDAY. THIS FEATURE MAY ALLOW THE TRADE WIND
INVERSION HEIGHT TO LIFT SLIGHTLY. THE INCREASED MOISTURE AND THE
HIGHER INVERSION COMBINED WITH SOME DYNAMIC LIFT AS THE MID-LEVEL
TROUGH ARRIVES MAY ALLOW THE COVERAGE OF TRADE SHOWERS TO INCREASE
ACROSS WINDWARD AND MAUKA AREAS STARTING AROUND MID-WEEK.

&&

.AVIATION...
FRESH AND GUSTY TRADE WINDS BENEATH A WELL DEFINED INVERSION ALOFT
ARE EXPECTED TO PERSIST TODAY. WIND SPEEDS IN EXCESS OF 25 KT ARE
EXPECTED ALONG NORTHEASTERN EXPOSURES AND OVER MOUNTAIN RIDGES...
WITH SOME LOCAL CHANNELED AREAS POTENTIALLY EXPERIENCING STRONGER
WIND GUSTS. AS A RESULT...AIRMET TANGO REMAINS IN EFFECT FOR
MODERATE LOW-LEVEL TURBULENCE IN THE AIR SPACE LEEWARD OF ALL
MOUNTAINS TODAY.

TRADE WIND SHOWERS ARE EXPECTED TO CONTINUE AFFECTING MAINLY
WINDWARD FACING SLOPES AND TERRAIN. LOW CLOUDS AND NUMEROUS SHOWERS
ACROSS THE NORTHEAST BIG ISLAND HAVE REQUIRED THE ISSUANCE OF AIRMET
SIERRA FOR MOUNTAIN OBSCURATION OVER THE WINDWARD BIG ISLAND. THESE
CONDITIONS ARE EXPECTED TO PERSIST BEYOND SUNRISE THIS MORNING.
BRIEF MVFR CIGS MAY ALSO OCCUR ALONG SOME WINDWARD SECTIONS OF THE
SMALLER ISLANDS...ESPECIALLY MAUI. OTHERWISE...VFR CONDS ARE
EXPECTED TO PREVAIL ACROSS MOST OTHER AREAS THROUGH THIS AFTERNOON.

&&

.MARINE...
THE CURRENT LARGE NORTH NORTHEAST SWELL CONTINUES TO SLOWLY SUBSIDE
EARLY THIS MORNING. THE MOST RECENT READINGS FROM THE HILO...
PAUWELA...MOKAPU AND WAIMEA BUOYS INDICATE THE SIGNIFICANT WAVE
HEIGHT IS STILL AROUND 9 FEET WITH A WAVE PERIOD OF ABOUT 13
SECONDS. AS A RESULT...THE HIGH SURF ADVISORY REMAINS IN EFFECT FOR
EAST FACING SHORES OF KAUAI...OAHU...MOLOKAI...MAUI AND THE BIG
ISLAND TODAY. THIS SWELL IS FORECAST TO GRADUALLY SHIFT TO A MORE
NORTHEASTERLY DIRECTION...WHICH COMBINED WITH LOCALLY GENERATED WIND
WAVES...WILL LIKELY KEEP SURF ELEVATED AND CHOPPY ALONG EAST FACING
SHORES THROUGH MOST OF THIS WEEKEND.

THE CURRENT NORTH NORTHEAST SWELL MAY ALSO CAUSE MODERATE HARBOR
SURGES WITHIN NORTH FACING HARBORS...SUCH AS KAHULUI AND HILO
HARBORS...THROUGH TODAY. LARGE BREAKING WAVES ARE ALSO POSSIBLE
NEAR THE ENTRANCES TO THESE NORTH FACING HARBORS. A MARINE WEATHER
STATEMENT HAS BEEN ISSUED TO COVER THIS POTENTIAL THREAT.

A SMALL CRAFT ADVISORY /SCA/ REMAINS IN EFFECT FOR ALL HAWAIIAN
COASTAL WATERS...EXCEPT THE LEEWARD MAUI COUNTY MARINE ZONE THROUGH
SATURDAY AFTERNOON DUE TO A COMBINATION OF STRONG TRADE WINDS AND
ROUGH SEAS. EVEN THOUGH SEAS MAY EVENTUALLY SUBSIDE LATER THIS
WEEKEND...THE TYPICALLY WINDY WATERS ADJACENT TO THE ISLANDS OF MAUI
AND HAWAII COUNTIES WILL LIKELY REMAIN IN THE SCA FROM SATURDAY
NIGHT INTO EARLY NEXT WEEK DUE TO THE TRADES REMAINING LOCALLY
STRONG.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THIS EVENING FOR EAST FACING
SHORES OF KAUAI...OAHU...MOLOKAI...MAUI AND THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR ALL HAWAIIAN
WATERS...EXCEPT THE MAUI COUNTY LEEWARD WATERS.

&&

$$

HOUSTON




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