AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 830 PM HST FRI JUL 8 2011 .SYNOPSIS... STRONG TRADE WINDS DUE TO A SURFACE HIGH FAR NORTH OF THE STATE WILL CONTINUE THROUGH SATURDAY...WITH A GRADUAL WEAKENING EXPECTED LATER THIS WEEKEND. AN UPPER LOW WILL APPROACH THE ISLANDS FROM THE EAST THIS WEEKEND...BEFORE IT PASSES JUST NORTH OF THE STATE EARLY NEXT WEEK. TRADE SHOWERS MAY BECOME ENHANCED BY THE UPPER LOW SATURDAY NIGHT THROUGH TUESDAY. HOWEVER...LOW CLOUDS AND SHOWERS WILL REMAIN FOCUSED MAINLY OVER WINDWARD AND MAUKA AREAS THROUGH NEXT WEEK. && .DISCUSSION... A NEARLY STATIONARY 1030 MB SURFACE HIGH IS CENTERED NEAR 38N 158W...OR ABOUT 1150 MILES NORTH OF HAWAII. THE TIGHT PRESSURE GRADIENT SOUTH OF THIS HIGH IS MAINTAINING THE STRONG TRADE WINDS ACROSS THE HAWAIIAN ISLANDS. ACCORDING TO LOOPS OF WATER VAPOR IMAGERY...THE ISLANDS ARE IN UNDER AN UPPER LEVEL COL BETWEEN LOW PRESSURE ALOFT TO THE WEST NORTHWEST AND EAST. THERE IS ALSO SIGNIFICANT SUBSIDENCE ALOFT ABOVE MOST OF THE STATE...WHICH IS CONTRIBUTING TO THE DRY AND STABLE CONDITIONS WE ARE EXPERIENCING. THE LOW TO THE EAST IS CENTERED NEAR 19N 144W... OR ABOUT 740 MILES EAST OF HILO. THIS LOW IS MOVING TOWARD THE NORTHWEST AT ABOUT 10 MPH. ALSO...MID-TROPOSPHERIC WINDS CONTINUE TO BE GUSTY AS A STRONG MID-LEVEL HIGH REMAINS PARKED FAR NORTH NORTHWEST OF THE ISLANDS. SUSTAINED WINDS OF AROUND 30 MPH WINDS WITH HIGHER GUSTS CONTINUE ACROSS THE HIGHER TERRAIN OF THE BIG ISLAND. THEREFORE...A WIND ADVISORY REMAINS IN EFFECT UNTIL EARLY SATURDAY MORNING FOR THE BIG ISLAND SUMMITS. THE FORECAST MODELS INDICATE WINDS AT THE HIGHER ELEVATIONS WILL DECREASE BY DAWN SATURDAY MORNING. THE AFTERNOON BALLOON SOUNDINGS AT HILO AND LIHUE SHOWED A INVERSION HEIGHTS AT AROUND 7 THOUSAND FEET AND 6 THOUSAND FEET... RESPECTIVELY. ALSO...PRECIPITABLE WATER /PW/ VALUES WERE 1.1 INCHES. SATELLITE DERIVED PW VALUES INDICATE EVEN DRIER AIR JUST UPSTREAM OF THE STATE. THEREFORE...EXPECT BREEZY...BUT RELATIVELY DRY TRADE WIND WEATHER TONIGHT...WITH THE EXCEPTION OF ISOLATED WINDWARD AND MAUKA TRADE SHOWERS. THE LOW-LEVEL TRADE WINDS WILL REMAIN STRONG ACROSS THE STATE INTO SATURDAY EVENING. AS THE HIGH TO THE NORTH BEGINS MOVING NORTH AND THE UPPER LEVEL LOW MOVES CLOSER TO THE ISLANDS...A WEAKENING TREND IN THE TRADES IS EXPECTED TO START LATE SATURDAY NIGHT...AND CONTINUE THROUGH MONDAY. TRADE WIND SPEEDS WILL REMAIN MODERATE INTO NEXT WEEK. THE PROXIMITY OF THE UPPER LEVEL LOW WILL LIKELY ENHANCE THE TRADE SHOWERS STARTING SATURDAY NIGHT...AND CONTINUING THROUGH TUESDAY. BY WEDNESDAY...THE FORECAST MODELS INDICATE THE UPPER LEVEL LOW WILL HAVE MOVED FAR NORTH OF THE STATE...AND THE ISLANDS SHOULD RETURN TO A MORE TYPICAL TRADE WIND WEATHER REGIME. THEREFORE...EXPECT CLOUDS AND SHOWERS TO REMAIN FOCUSED PRIMARILY OVER WINDWARD AND MAUKA AREAS WITH MOST RAINFALL OCCURRING DURING THE NIGHT AND EARLY MORNING HOURS STARTING IN THE MIDDLE OF NEXT WEEK. && .AVIATION... DUE TO THE STRONG TRADES...AIRMET TANGO REMAINS IN EFFECT FOR ISOLATED SEVERE TURBULENCE BELOW 8 KT S THRU W OF HIGHER TERRAIN ON LANAI...MAUI AND THE BIG ISLAND. THERE IS ALSO AN AIRMET INCLUDES LOW LEVEL TURBULENCE FOR AREAS BELOW 7 KFT S THRU W OF THE HIGHER TERRAIN ON KAUAI...OAHU AND MOLOKAI...AND FROM 8 TO 15 KFT S THRU W OF THE TERRAIN ON LANAI...MAUI AND THE BIG ISLAND. && .MARINE... A SMALL CRAFT ADVISORY /SCA/ REMAINS IN EFFECT FOR ALL HAWAIIAN WATERS DUE TO THE STRONG AND GUSTY TRADES ALONG WITH ROUGH SEAS OF 10 FEET OR GREATER IN MANY LOCATIONS. THESE STRONG TRADES ARE FORECAST TO REMAIN INTO SATURDAY EVENING...BEFORE STARTING TO TAPER OFF LATE SATURDAY NIGHT. THE CURRENT FORECAST HAS THE SCA CONDITIONS LIMITED TO THE TYPICALLY WINDY WATERS ADJACENT TO MAUI AND THE BIG ISLAND STARTING LATE SATURDAY NIGHT...WITH WINDS / SEAS DROPPING BELOW THE SCA CRITERIA ON SUNDAY IN THOSE LOCATIONS ALSO. THE CURRENT LARGE SOUTH SOUTHWEST SWELL WILL CONTINUE TO PRODUCE SURF HEIGHTS AT OR ABOVE THE HIGH SURF ADVISORY CRITERIA ALONG SOUTH FACING SHORES OF ALL HAWAIIAN ISLANDS TONIGHT. THIS SWELL WILL GRADUALLY LOWER SATURDAY...WITH SURF HEIGHTS EXPECTED TO GRADUALLY DIMINISH BELOW THE HIGH SURF ADVISORY THRESHOLD OF 8 FEET BY SATURDAY EVENING. ELSEWHERE...ROUGH AND CHOPPY SURF ALONG EAST FACING SHORES AND REEFS REMAINS ELEVATED DUE TO THE STRONG TRADE WINDS. THEREFORE...EAST FACING SHORES OF KAUAI...OAHU...MOLOKAI...MAUI AND THE BIG ISLAND WILL REMAIN UNDER A HIGH SURF ADVISORY AT LEAST THROUGH SATURDAY AFTERNOON. BEYOND THIS WEEKEND...ANOTHER SMALL...BUT RELATIVELY LONG-PERIOD... SOUTH SWELL IS FORECAST TO AFFECT SOUTH FACING SHORES OF THE ISLANDS THROUGH THE MIDDLE OF NEXT WEEK. THE ARRIVAL OF A LARGER SOUTH SWELL IS EVIDENT IN THE OUTPUT FROM THE WAVE WATCH III MODEL OUTPUT STARTING NEXT THURSDAY NIGHT AND CONTINUING THROUGH FRIDAY. && .HFO WATCHES/WARNINGS/ADVISORIES... HIGH SURF ADVISORY UNTIL 600 PM SATURDAY FOR SOUTH FACING SHORES OF ALL ISLANDS. HIGH SURF ADVISORY UNTIL 600 PM SATURDAY FOR EAST FACING SHORES OF KAUAI...OAHU...MOLOKAI...MAUI AND THE BIG ISLAND. WIND ADVISORY UNTIL 600 AM HST SATURDAY FOR BIG ISLAND SUMMITS. SMALL CRAFT ADVISORY UNTIL 600 PM HST SATURDAY FOR ALL HAWAIIAN WATERS. && $$