847 FXHW60 PHFO 231412 CCA AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 400 AM HST SAT MAR 23 2013 .SYNOPSIS... CLOUDS AND SHOWERS ASSOCIATED WITH A WEAK FRONTAL BOUNDARY OVER MAUI COUNTY WILL CONTINUE TO AFFECT MOST OF THE STATE THIS WEEKEND. THE FRONT WILL STALL AND TRANSITION TO A TROUGH THAT WILL LINGER IN THE VICINITY OF THE CENTRAL ISLANDS INTO EARLY NEXT WEEK. THE REMNANT MOISTURE ASSOCIATED WITH THIS FEATURE WILL REMAIN ACROSS THE STATE...BRINGING WET WEATHER...ESPECIALLY ACROSS PORTIONS OF THE WESTERN ISLANDS...FOR THE NEXT SEVERAL DAYS. && .DISCUSSION... A SHALLOW NORTH NORTHEAST TO SOUTH SOUTHWEST ORIENTED FRONTAL BOUNDARY HAS MOVED ACROSS WESTERN AND CENTRAL MOLOKAI OVERNIGHT BASED ON SURFACE OBSERVATIONS...THE VAD WIND PROFILE FROM THE MOLOKAI RADAR AND SATELLITE BASED SCATTEROMETER OBSERVATIONS. THE FRONT APPEARS TO BE NEAR EASTERN MOLOKAI AND LANAI AROUND 300 AM HST THIS MORNING. ELSEWHERE...A 1026 MB SURFACE HIGH IS LOCATED FAR WEST NORTHWEST OF KAUAI. THE ROUNDED EASTERN END OF A SURFACE RIDGE EXTENDS FROM THIS HIGH THROUGH A POINT ABOUT 200 MILES NORTH OF KAUAI. AS A RESULT...THE LOW-LEVEL FLOW OVER KAUAI AND OAHU IS FROM THE NORTHEAST. EAST OF THE FRONT...THE WINDS REMAIN LIGHT AND ARE GENERALLY FROM A SOUTH TO SOUTHEAST DIRECTION. WATER VAPOR IMAGERY SHOWS THE AXIS OF THE UPPER LEVEL TROUGH...WHICH WAS SUPPORTING THIS FRONT HAS SHIFTED FAR NORTH NORTHEAST OF THE ISLANDS. WITH THE LOSS OF THIS UPPER LEVEL SUPPORT...ALONG WITH THE FACT THERE IS NORTHEASTERLY FLOW WEST OF THE FRONT AND SOUTHEASTERLY FLOW TO THE EAST...IT APPEARS THE FRONTAL BOUNDARY IS ALREADY BEGINNING TO TRANSITION INTO A SURFACE TROUGH. ANOTHER UPPER LEVEL TROUGH IS LOCATED FAR WEST OF KAUAI. SATELLITE IMAGERY SHOWS BROKEN TO OVERCAST CIRRUS CLOUDS OVER MOST OF THE ISLAND CHAIN. THESE HIGH CLOUDS ARE OBSCURING MOST OF THE LOW CLOUDS BELOW IN INFRARED SATELLITE IMAGERY. THE HIGH CLOUDS...WHICH CONSIST MAINLY OF ICE CRYSTALS...ARE BEING TRANSPORTED BY AN UPPER LEVEL SUBTROPICAL JET STREAM THAT IS ALONG THE EAST FLANK OF THE SECOND UPPER LEVEL TROUGH LOCATED FAR WEST OF KAUAI. RADAR REFLECTIVITY DATA SHOWS SHOWERS WITH LIGHT TO MODERATE RAINFALL ALONG THE FRONTAL BAND IN THE VICINITY OF LANAI...EASTERN MOLOKAI AND WEST MAUI. ADDITIONAL LIGHT TO MODERATE SHOWERS ARE OVER THE KAIWI CHANNEL AND JUST WEST OF THE LEEWARD BIG ISLAND COAST. ISOLATED LIGHT SHOWERS ARE IN THE VICINITY OF OAHU AND THE SOUTHEASTERN BIG ISLAND COAST, MOISTURE ASSOCIATED WITH THE FRONTAL BOUNDARY WILL REMAIN IN THE VICINITY OF THE ALOHA STATE...PROVIDING LOW CLOUDS AND SHOWERS. THE SATELLITE DERIVED PRECIPITABLE WATER VALUES OVER THE CENTRAL ISLANDS ARE ESTIMATED TO BE ABOUT 1.4 INCHES...WITH LESSER VALUES TOWARD KAUAI. THE PRESENCE OF THE WEAK SURFACE FRONT IS ALSO KEEPING THE SURFACE PRESSURE GRADIENT FAIRLY WEAK OVER THE REGION. THEREFORE... SURFACE WINDS ARE EXPECTED TO REMAIN ON THE LIGHTER SIDE...EXCEPT FOR KAUAI AND OAHU WHICH WILL EXPERIENCE SLIGHTLY STRONGER NORTHEASTERLY FLOW FOR THE NEXT 24 TO 30 HOURS TO THE WEST OF THE FRONT / TROUGH. THE TROUGH IS EXPECTED TO LINGER ACROSS THE ISLANDS INTO EARLY NEXT WEEK. FORECAST MODELS INDICATE UPPER LEVEL SHORT WAVES WILL ALSO MOVE ACROSS THE ISLANDS DURING THE NEXT FEW DAYS. THE PASSAGE OF THESE UPPER LEVEL FEATURES IS EXPECTED TO PRODUCE A SLIGHT DESTABILIZATION OF THE AIR MASS OVER THE REGION. WITH THE LINGERING MOISTURE IN THE VICINITY OF THE ISLANDS...THE STATE WILL LIKELY HAVE MORE WIDESPREAD LOW CLOUDS AND SHOWERS. THE PRESENCE OF THE TROUGH WILL ALSO LIKELY KEEP WINDS RELATIVELY LIGHT. THE SUBTROPICAL JET STREAM WILL ALSO PERSIST AT THE UPPER LEVELS ABOVE THE STATE...WHICH WILL CONTINUE TO BRING HIGH CLOUDS ACROSS THE REGION...KEEPING SKIES SOMEWHAT CLOUDY FROM THIS WEEKEND INTO EARLY NEXT WEEK. TRADE WINDS MAY FINALLY RETURN TO THE ISLANDS TOWARDS THE MIDDLE OF NEXT WEEK...AS THE SURFACE TROUGH EVENTUALLY DISSIPATES...AND SURFACE HIGH PRESSURE BUILDS FAR NORTH OF THE ISLANDS. SHOWERS CARRIED BY THE TRADES WILL MAINLY AFFECT WINDWARD AND MAUKA SECTIONS OF THE ISLANDS. && .AVIATION... MOISTURE IN THE FORM OF LOW CLOUDS AND SHOWERS ASSOCIATED WITH A WEAKENING FRONT OVER THE CENTRAL ISLANDS WILL PRODUCE AREAS OF MVFR...AND ISOLATED IFR CONDITIONS...ESPECIALLY OVER PORTIONS OF MAUI COUNTY EARLY THIS MORNING. AN AIRMET FOR MOUNTAIN OBSCURATION IS CURRENTLY IN EFFECT FOR THE HIGHER TERRAIN ON MAUI...LANAI... MOLOKAI...OAHU AND KAUAI. THESE CONDITIONS MAY PERSIST THROUGH THIS AFTERNOON AS THE FRONT TRANSITIONS TO A SURFACE TROUGH...WHICH IS EXPECTED TO STALL OVER THE CENTRAL ISLANDS LATER TODAY. && .MARINE... THE CURRENT NORTHWEST SWELL CONTINUES TO SUBSIDE EARLY THIS MORNING...WITH THE SIGNIFICANT WAVE HEIGHT AT THE WAIMEA BAY BUOY DOWN TO 6 FEET WITH A PERIOD OF 13 SECONDS. A LONG PERIOD NORTHWEST SWELL ARRIVING LATE SUNDAY WILL PRODUCE MODERATE SURF HEIGHTS ALONG NORTH AND WEST FACING SHORES OF THE SMALLER ISLANDS...WHICH WILL PEAK BELOW THE HIGH SURF ADVISORY CRITERIA ON MONDAY. THIS SWELL WILL GRADUALLY SUBSIDE FROM TUESDAY THROUGH WEDNESDAY. SMALL SOUTH SWELLS WILL MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES THROUGH THE MIDDLE OF NEXT WEEK. NO SMALL CRAFT ADVISORY CONDITIONS ARE FORECAST FOR THE HAWAIIAN COASTAL WATERS INTO THE MIDDLE OF NEXT WEEK. && .HFO WATCHES/WARNINGS/ADVISORIES... NONE. && $$ HOUSTON