AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST THU JUL 7 2011

.SYNOPSIS...
FRESH TO LOCALLY STRONG TRADE WINDS WILL CONTINUE THROUGH FRIDAY
WITH A GRADUAL DECREASE EXPECTED THIS WEEKEND AND MONDAY. TRADE
WINDS WILL REMAIN MODERATE THROUGH NEXT WEEK. CLOUDS AND SHOWERS
FOCUS ON WINDWARD/MAUKA AREAS THROUGH THE FORECAST PERIOD WITH MOST
RAIN OCCURRING DURING THE NIGHT AND EARLY MORNINGS. AN UPPER LOW
WILL APPROACH FROM THE EAST SUNDAY AND SKIRT NEAR BUT TO THE NORTH
OF THE ISLAND CHAIN WHICH MAY ENHANCE THE SHOWERS A BIT SUNDAY NIGHT
THROUGH TUESDAY.

&&

.DISCUSSION...
A SURFACE HIGH LOCATED AT 38N 155W...FAR NORTH OF THE HAWAIIAN
ISLANDS THIS AFTERNOON AND IS DRIVING FRESH TO LOCALLY STRONG TRADE
WINDS ACROSS THE AREA. THE AFTERNOON SOUNDING AT HILO SHOWED A HIGH
INVERSION LEVEL AND DEEP LAYERED TRADE WINDS...WHICH IS CAUSING THE
TRADES TO REACH SUMMIT LEVELS ON THE BIG ISLAND AND MAUI. WINDS HAVE
BEEN SUSTAINED AT 30 MPH WITH GUSTS TO 40 MPH TODAY AND A WIND
ADVISORY IS IN EFFECT THROUGH FRIDAY MORNING. PRECIPITABLE WATER /PW/
VALUES WERE 1.50 INCHES AT HILO AND AMSU/SSMI SATELLITE DERIVED PW
SHOW A SMALL FETCH OF MOIST AIR UPSTREAM OF THE STATE. FOR
TONIGHT...EXPECTING TO SEE PASSING WINDWARD/MAUKA SHOWERS WITH
OCCASIONAL SHOWERS BLOWING TO LEEWARD SIDES DUE TO THE ELEVATED
TRADES. THESE SHOWERS WILL BEGIN TO WANE BY FRIDAY MORNING AS THE
HUMIDITY LOWERS AND DRIER AIR UPSTREAM FINALLY MAKES IT TO THE
ISLANDS.

THE SURFACE HIGH WILL REMAIN NEARLY STATIONARY THROUGH SATURDAY
BEFORE MOVING FARTHER NORTH BEGINNING SUNDAY.  ALOFT...WATER VAPOR
IMAGERY SHOWS AN UPPER LEVEL LOW CENTERED AT 21N 135W...OR 1500
MILES WEST OF HONOLULU...MOVING EAST TOWARDS THE STATE. AS THIS
FEATURE NEARS OUR AREA...IT WILL BEGIN TO INDUCE TROUGHING TO OUR
SOUTHEAST AND RESULT IN A DECREASED PRESSURE GRADIENT OVER THE
ISLANDS. THE RESULT WILL BE A SLOW AND GRADUAL WEAKENING OF THE
TRADE WINDS THIS WEEKEND. THE WINDS ARE THEN EXPECTED TO WEAKEN
FURTHER DOWN TO MODERATE BREEZES AS THE SURFACE HIGH ALSO BEGINS TO
MOVE AWAY FROM THE AREA. AS THE WINDS DECREASE...WILL SEE LESS
LEEWARD SHOWERS THROUGH THE WEEKEND. CLOUDS AND SHOWERS FOCUS ON
WINDWARD/MAUKA AREAS WITH MOST RAIN OCCURRING DURING THE NIGHT AND
EARLY MORNINGS.

THE UPPER LOW IS EXPECTED TO SKIRT NEARBY BUT TO THE NORTH OF THE
ISLAND CHAIN WHICH MAY ENHANCE THE SHOWERS A BIT SUNDAY NIGHT
THROUGH TUESDAY. THE PATH OF THE UPPER LEVEL LOW IS BROUGHT MUCH
CLOSER TO THE STATE BY THE ECMWF THAN THE GFS...BUT THERE IS GENERAL
AGREEMENT WITH THE SYSTEM BEGINNING TO LIFT AWAY FROM THE AREA BY
TUESDAY.

&&

.AVIATION...
DUE TO STRONG TRADES...AIRMET TANGO WILL CONTINUE FOR LOW LEVEL
TURBULENCE FOR AREAS BELOW 080 S THRU W OF MOUNTAINS FOR THE MAIN
HAWAIIAN ISLANDS. ASSOCIATED TRADE SHOWERS WILL BRIEFLY LOWER
CEILINGS AND VISIBILITY TO MVFR CONDITIONS OVERNIGHT ON WINDWARD TAF
SITES. HOWEVER...VFR CONDITIONS WILL PREVAIL THROUGHOUT THE FORECAST
PERIOD.


&&

.MARINE...
FRESH TRADE WIND BACKGROUND FLOW WILL PRODUCE ACCELERATED WINDS
THROUGH THE HAWAIIAN CHANNELS. SMALL CRAFT ADVISORY /SCA/ CONDITIONS
WILL CONTINUE FOR ALL CHANNELS AND TYPICALLY WINDY ZONES AROUND MAUI
COUNTY AND THE BIG ISLAND. THE SCA GOES THROUGH SATURDAY...BUT A FEW
OF THE WINDER ZONES COULD BE EXTENDED INTO SATURDAY NIGHT. THE
EXPECTED DECREASE IN TRADE WINDS WILL LIKELY ALLOW DROPPING ALL
ZONES BY SUNDAY.

A SOLID S-SSW SWELL IS CURRENTLY IMPACTING SOUTH FACING SHORES OF
ALL ISLANDS AND A HIGH SURF ADVISORY IS IN EFFECT. ANOTHER SWELL IS
EXPECTED TO ARRIVE FRIDAY AND SATURDAY WHICH WILL KEEP ADVISORY
LEVEL SURF ALONG SOUTH FACING SHORES THROUGH SATURDAY. THE ELEVATED
TRADE WINDS WILL ALSO PRODUCE SHORT PERIOD SURF WILL CREATE ROUGH
CONDITIONS ALONG EAST FACING SHORES OF KAUAI OAHU MOLOKAI MAUI AND
THE BIG ISLAND. A HIGH SURF ADVISORY IS NOW IN EFFECT FOR EAST
FACING SHORES OF THESE ISLANDS.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM SATURDAY FOR SOUTH FACING SHORES OF
ALL ISLANDS. HIGH SURF ADVISORY FOR UNTIL 6 PM SATURDAY EAST FACING
SHORES OF KAUAI OAHU MOLOKAI MAUI THE BIG ISLAND.

WIND ADVISORY UNTIL 6 AM HST FRIDAY FOR HALEAKALA SUMMIT-BIG
ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR KAUAI CHANNEL-
KAIWI CHANNEL-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG
ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.


&&

$$