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| RH | | 9 % |
| Wind | | ESE 20 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 169 FXHW60 PHFO 191340 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 340 AM HST SAT APR 19 2014 .SYNOPSIS... A TRADE WIND WEATHER PATTERN WILL CONTINUE THROUGH THE NEXT SEVERAL DAYS ACROSS HAWAII...THANKS TO HIGH PRESSURE NORTH OF THE STATE. SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS WITH A FEW SHOWERS POSSIBLE OVER SOME LEEWARD LOCATIONS. && .DISCUSSION... SHOWERS HAVE BECOME RATHER SPARSE OVER THE STATE DURING THE PAST SEVERAL HOURS...WITH RADAR AND RAIN GAUGE DATA SHOWING ONLY VERY LIGHT RAINFALL AMOUNTS ACROSS SOME WINDWARD AREAS. THE 12Z SOUNDINGS SHOW A LOWERING OF THE INVERSION AS EXPECTED...WITH THE BASE DOWN TO BETWEEN 5700 AND 6700 FEET...FROM ABOUT 9000 FEET 12 HOURS EARLIER. THIS IS CONSISTENT WITH MIMIC-TPW SATELLITE DATA WHICH INDICATE A DRIER AIRMASS SPREADING INTO THE STATE FROM THE EAST. EARLIER MODEL DATA SUGGESTED THAT THIS DRYING WOULD TAKE PLACE PRIMARILY IN THE 850-700 MB LAYER...AGAIN CONSISTENT WITH THE 12Z RAOB DATA. SATELLITE IMAGERY DEPICTS ABUNDANT HIGH LEVEL CLOUDINESS STREAMING NORTHWARD ACROSS THE STATE...TO THE EAST OF A MID/UPPER LEVEL TROUGH CENTERED SEVERAL HUNDRED MILES TO THE SOUTHWEST. AT THE SURFACE...A 1023 MB HIGH IS CENTERED WELL NORTHEAST OF THE STATE...WITH A STRONGER 1028 MB HIGH BUILDING EASTWARD FROM THE DATELINE NORTH OF 30N. FOR TODAY...EXPECT SHOWER COVERAGE TO REMAIN FAIRLY SPARSE WITH LIGHT RAINFALL AMOUNTS EVEN ACROSS WINDWARD SECTIONS...AS STABLE AND DRY CONDITIONS CONTINUE. TONIGHT...SATELLITE AND MODEL DATA INDICATE THAT ANOTHER AREA OF HIGHER MOISTURE WILL BE MOVING INTO THE STATE...ALTHOUGH MODEL SOUNDINGS SHOW THE INVERSION REMAINING FAIRLY LOW. WITH BRISK TRADES IN PLACE...THE INFLUX OF ADDITIONAL LOW LEVEL MOISTURE SHOULD BE SUFFICIENT TO INCREASE SHOWER ACTIVITY ONCE AGAIN ACROSS WINDWARD/MAUKA AREAS...WITH SOME SPILLOVER INTO LEEWARD. SUNDAY THROUGH MONDAY NIGHT...RATHER STRONG HIGH PRESSURE WILL PASS NORTH OF THE STATE...CAUSING TRADES TO INCREASE FURTHER. ALOFT...GUIDANCE INDICATES THAT THE MID/UPPER TROUGH TO OUR SOUTHWEST WILL SHEAR APART...WITH THE MID LEVEL TROUGH MOVING TO THE WEST SOUTHWEST AND AWAY FROM OUR AREA...WHILE THE WEAKENING UPPER LEVEL TROUGH DRIFTS SLOWLY TO THE EAST NORTHEAST. A DEEP DRY LAYER WILL PERSIST ACROSS THE STATE IN THE MID LEVELS...WITH A MID LEVEL RIDGE BUILDING JUST TO OUR NORTH. THEREFORE WOULD EXPECT THE ONLY IMPACT TO OUR SENSIBLE WEATHER FROM THE UPPER TROUGH TO BE PERIODS OF HIGH LEVEL CLOUDINESS. ACTIVE TRADE SHOWERS WILL CONTINUE ACROSS WINDWARD/MAUKA...WITH SOME SPILLOVER TO LEEWARD DUE TO THE STRENGTH OF THE TRADES. TRADES SHOULD RETURN TO MORE MODERATE LEVELS TUESDAY THROUGH THURSDAY...AS THE FIRST SURFACE HIGH SHIFTS FURTHER TO THE NORTHEAST AND IS REPLACED BY A SECOND SLIGHTLY WEAKER HIGH TO OUR NORTH. WOULD EXPECT LITTLE CHANGE IN THE WEATHER PATTERN ACROSS HAWAII WITH SHOWERS CONTINUING MAINLY ACROSS WINDWARD SECTIONS. && .AVIATION... A TRADE WIND FLOW CONTINUES WITH EMBEDDED SHOWERS FAVORING THE WINDWARD AND MTN AREAS. BUT IT APPEARS THIS FLOW HAS BECOME DRIER AS THE NIGHT PROGRESSES. FIRST IS THE MARINE LAYER WHICH HAS LOWERED FROM 10K EARLY IN THE EVENING TO THE CURRENT...BETWEEN 6 AND 7K FEET. SECOND...RADAR RETURNS ARE NOT AS ACTIVE AS AT THE START OF THE EVENING. THE SHOWERS HAVE TURNED LIGHTER TO PERHAPS MORE OF A DRIZZLE. THIRD...SFC OBS FROM AROUND THE STATE SUGGEST THE LO CLD COVER ESPECIALLY FROM THE WINDWARD STATIONS...HAS BECOME LESS. CLOUD BASES THOUGH REMAINS AS LOW AS 2K FEET. MODELS SUGGESTS THIS DRIER AIR MASS TO PERSISTS THROUGH ALL OF TODAY. HENCE...VFR CONDITION RULES. ANY MVFR DUE TO CEILINGS AND VIS WILL BE BRIEF AND ISOLATED AND FAVORING THE WINDWARD AND MTN AREAS. LITTLE CHANGE TO THE STRENGTH OF THE TRADE WINDS WHICH WILL BE IN THE MODERATE TO STRONG RANGE. GIVEN A DECENT INVERSION...AIRMET TANGO FOR MOD MECHANICAL TURB WILL CONT TO WELL BEYOND 04Z SUNDAY. && .MARINE... AN 0830Z ASCAT PASS ONLY CAUGHT THE WESTERN EDGE OF THE COASTAL WATERS...BUT DID SHOW SIGNIFICANT COVERAGE OF 23-25 KT WINDS WEST AND SOUTH OF KAUAI. THESE WINDS ARE SEVERAL KNOTS ABOVE GUIDANCE... BUT THIS DATA COMBINED WITH AVAILABLE LAND STATION OBS SUPPORT EXPANDING THE SMALL CRAFT ADVISORY TO COVER ALL HAWAIIAN COASTAL WATERS. WINDS SHOULD ONLY INCREASE FURTHER WITH TIME AS HIGH PRESSURE BUILDS TO OUR NORTH...AND HAVE ALSO EXTENDED THE SCA IN TIME OUT THROUGH MONDAY. WINDS MAY REACH NEAR GALE FORCE AT TIMES SUNDAY THROUGH MONDAY IN THE ALENUIHAHA CHANNEL. ANOTHER SMALL NORTHWEST SWELL IS EXPECTED TO ARRIVE LATER TODAY AND LINGER THROUGH SUNDAY...BUT THE RESULTING SURF WILL REMAIN WELL BELOW ADVISORY LEVELS FOR NORTH AND WEST FACING SHORES. TRADE WINDS WILL CONTINUE TO PRODUCE SHORT PERIOD CHOPPY SURF ALONG EAST FACING SHORES...AND HIGH SURF ADVISORIES WILL PROBABLY BE NEEDED BY SUNDAY AS THE FETCH LENGTH INCREASES DUE TO THE BUILDING HIGH TO OUR NORTH. && .HFO WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR ALL HAWAIIAN WATERS. && $$ DISCUSSION/MARINE...JACOBSON AVIATION...LAU Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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