| Current Conditions | ||
| Temp |  | 0.2 C |
| RH | | 12 % |
| Wind | | SE 15 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 974 FXHW60 PHFO 241330 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 400 AM HST THU APR 24 2014 .SYNOPSIS... BREEZY AND GUSTY TRADE WINDS WILL STRENGTHEN GRADUALLY INTO FRIDAY...AND THEN DIMINISH FROM SUNDAY INTO NEXT WEEK. A MOISTER AIR MASS WILL BRING MORE SHOWERS AROUND FRIDAY...BUT OTHERWISE RAINFALL WILL BE LIGHT...AND FOCUSED MAINLY OVER WINDWARD SLOPES... THOUGH THE WIND WILL CARRY SOME SHOWERS LEEWARD BEFORE THEY DISSIPATE. && .DISCUSSION... SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED MODERATE TRADE WINDS BLOWING...WHILE PRESSURE TRENDS SUGGESTED LITTLE CHANGE THROUGH THE SHORT RUN. CLOUD COVER UPWIND OF THE STATE WAS FAIRLY TYPICAL OVERALL...WITH AN ARC OF MORE EXTENSIVE LOW CLOUDS AFFECTING MAINLY KAUAI...BUT SPREADING SOUTH TOWARD OAHU AND MAUI COUNTY. MOST PRECIPITATION OVER LAND REMAINED LIMITED TO WINDWARD SLOPES...WHERE IT RECEIVED SUPPORT FROM OROGRAPHIC FORCING. THREE-HOUR ACCUMULATION FOLLOWED THE CLOUD TRENDS. ALOFT...WEAK TROUGHING TO THE SOUTHWEST MOVED FURTHER AWAY FROM THE ISLANDS...WHILE BROAD RIDGING EXPANDED OVER THE STATE FROM THE NORTH NORTHWEST. GUIDANCE PREDICTED THIS MID-LEVEL RIDGE TO PERSIST THROUGH ABOUT SATURDAY...PROVIDING SUBSTANTIAL SUPPORT TO THE SUBTROPICAL RIDGE AT THE SURFACE TO THE NORTHEAST. INCREASING WIND SPEEDS MAY APPROACH THE CRITERION FOR A WIND ADVISORY AROUND FRIDAY. LOCAL STABILITY ALSO SHOULD BUILD WITH TIME...BUT THE FULL INFLUENCE OF THE RIDGE HAD NOT YET BEGUN TO TAKE EFFECT...LEAVING THE INVERSION HIGHER THAN USUAL FOR THE TIME BEING. DRY TRADE-WIND CONDITIONS WILL PREVAIL THROUGH MOST OF THE FORECAST PERIOD. HOWEVER...OROGRAPHIC FORCING WILL CONTINUE TO SQUEEZE OUT AT LEAST A LITTLE RAIN OVER WINDWARD SLOPES...ESPECIALLY FROM FRIDAY INTO FRIDAY NIGHT...WHEN MOST SOLUTIONS PREDICTED A SOMEWHAT MOISTER AIR MASS TO PASS. FROM LATE SUNDAY INTO THE EARLY PART OF NEXT WEEK...THE RIDGE ALOFT WILL SHIFT QUITE FAR EAST...LIMITING ITS INFLUENCE LOCALLY. SOME MODELS HINTED THAT THE OLD MID-LEVEL LOW MAY RETURN FROM THE WEST AS AN OPEN...IF SHALLOW...TROUGH ON A BROADER AND DEEPER TROUGH APPROACHING FROM THE NORTH NORTHWEST. THIS LATE IN THE SEASON...THE DEEPER TROUGH WILL BE VERY UNLIKELY TO HAVE MUCH LOCAL EFFECT...BUT THE SHALLOWER ONE MAY BE ABLE TO WEAKEN THE SUBTROPICAL RIDGE...AND THUS THE TRADE WINDS...THROUGH THIS PERIOD. BY THE TIME THAT THE SURFACE FRONT ASSOCIATED WITH THE DEEPER TROUGH ARRIVES AROUND WEDNESDAY...IT SHOULD BE LIMITED TO LITTLE MORE THAN A SLIGHT WIND SHIFT...AND A BIT OF CONVERGED MOISTURE SUPPORTING THE WINDWARD SHOWERS. MORE TYPICAL TRADE-WIND CONDITIONS WILL RETURN THROUGH THE SECOND HALF OF NEXT WEEK AS ANOTHER MID-LEVEL RIDGE BUILDS IN FROM THE WEST. && .MARINE... A SMALL CRAFT ADVISORY /SCA/ REMAINED IN EFFECT FOR ALL WATERS IN ANTICIPATION OF STRENGTHENING WINDS AND BUILDING COMBINED SEAS THROUGH FRIDAY AFTERNOON...BUT MAY BE REDUCED IN AREA TO THE TYPICALLY WINDY WATERS AROUND THE BIG ISLAND AND MAUI ON SATURDAY NIGHT OR SUNDAY. THE NORTHEASTERLY WINDS WILL REACH THEIR MINIMUM SPEEDS LATE SUNDAY OR MONDAY...AND THEN INCREASE AGAIN BY THE MIDDLE OF NEXT WEEK. THE PERSISTENT TRADE WINDS WILL BUILD SEAS...PRODUCING ROUGH SURF NEAR THE ADVISORY LEVEL ALONG EAST-FACING SHORES BY FRIDAY. THE INCREASING SEAS ALSO WILL CONTRIBUTE TO THE NEED FOR AN EXPANDED SCA. SEAS WILL DIMINISH WITH THE WINDS LATE SATURDAY AND SUNDAY. A NORTHWEST SWELL THAT BUILD OVERNIGHT WILL PRODUCE SIGNIFICANT WAVE HEIGHTS JUST BELOW THE NORTH-SHORE ADVISORY CRITERION ON THE SMALLER ISLANDS TODAY. THE SWELL WILL DROP FRIDAY AND SATURDAY...BUT A SMALL REINFORCING NORTHWEST SWELL MAY ARRIVE LATE SUNDAY INTO TUESDAY. SOUTH-FACING SHORES HAVE BEEN RECEIVING SOME SWELL ENERGY FROM THE SOUTHWEST. THIS SWELL WILL FADE ON FRIDAY...BUT SMALL SWELL FROM THE SOUTH SOUTHEAST MAY ARRIVE OVER THE WEEKEND. && .HFO WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR ALL HAWAIIAN WATERS- && $$ RYSHKO Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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