| Current Conditions | ||
| Temp |  | 0.4 C |
| RH | | 17 % |
| Wind | | SW 7 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 202 FXHW60 PHFO 180646 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 845 PM HST FRI MAY 17 2013 .SYNOPSIS... TRADE WINDS WILL WEAKEN TONIGHT AND SATURDAY...AS LOW PRESSURE DEVELOPS NORTH OF THE ISLANDS. THE WEAK LOW WILL TURN WINDS TO THE NORTH ON KAUAI AND OAHU BY SATURDAY NIGHT...WITH LIGHT SOUTH WINDS NEAR THE BIG ISLAND. WITH LIGHT WINDS...CLOUDS AND SHOWERS WILL FAVOR AFTERNOON HOURS...AND THE INTERIOR AND UPSLOPE AREAS. THE PRESENCE OF THE LOW WILL HELP TO INTENSIFY ANY SHOWERS THAT FORM OVER THE ISLANDS FOR THE NEXT SEVERAL DAYS. && .DISCUSSION... CURRENTLY...WATER VAPOR IMAGERY SHOWS A CLOSED LOW ALOFT CENTERED NEAR OAHU...MOVING SLOWLY TOWARD THE ESE AT ABOUT 5 MPH. AT THE SURFACE...MODERATE TRADE WINDS ARE BEING SUPPORTED BY A SURFACE HIGH CENTERED ABOUT 1300 MILES NE OF THE ISLANDS. THE PRESENCE OF THE LOW ALOFT HAS DESTABILIZED THE ISLAND AIRMASS...AND IS ENHANCING BOTH THE INCOMING TRADE WIND SHOWERS...AND THE SHOWERS LINGERING OVER THE KONA SLOPES THAT FORMED IN RESPONSE TO AFTERNOON SEABREEZES AND UPSLOPE FLOW. MEANWHILE...WATER VAPOR AND INFRARED IMAGERY SHOW A DEVELOPING AREA OF LOW PRESSURE ABOUT 600 MILES NORTH OF THE ISLANDS...NEAR 30N 158W...WHICH WILL BECOME AN IMPORTANT PLAYER IN ISLAND WEATHER OVER THE NEXT SEVERAL DAYS. THE FORECAST CALLS FOR THE CURRENT UPPER LOW TO MOVE ESE WHILE SLOWLY WEAKENING THROUGH SATURDAY...WHILE A NEW TROUGH ALOFT DIGS AGGRESSIVELY SE OVER WATERS NW AND N OF THE ISLANDS. THIS STRONGLY DIGGING TROUGH WILL HELP TO DEVELOP A CLOSED LOW ALOFT THAT WILL MEANDER IN A POSITION ABOUT 550 MILES NE OF THE ISLANDS FROM LATE SATURDAY INTO THE MIDDLE OF NEXT WEEK. THE PROXIMITY OF THE CLOSED LOW WILL MAINTAIN A MODERATELY UNSTABLE ISLAND AIRMASS...AND ENHANCE ANY SHOWERS THAT DEVELOP. THE LOW WILL LINGER N OF THE ISLANDS UNTIL THE MIDDLE OF NEXT WEEK BEFORE FINALLY DISSIPATING. A WEAK SURFACE LOW IS FORECAST TO DEVELOP IN RESPONSE TO THE DEVELOPING LOW ALOFT TO THE N OF THE ISLANDS...WITH A SURFACE TROUGH EXTENDING S OVER THE ISLANDS. THIS WILL INTERRUPT THE TRADE FLOW OVER THE NEXT 24 HOURS... AND ALTHOUGH THERE IS SOME UNCERTAINTY AS TO WHERE THE TROUGH AXIS WILL LIE...LATEST GUIDANCE INDICATES THAT LIGHT TO MODERATE WINDS WILL TURN TO THE N OVER KAUAI AND OAHU BY SUNDAY...WITH S WINDS NEAR THE BIG ISLAND. AWAY FROM THE MODERATE N FLOW ON KAUAI...LAND AND SEA BREEZE CIRCULATIONS WILL DOMINATE WIND FLOW OVER THE ISLANDS. THIS MEANS AFTERNOON CLOUDS AND SHOWERS OVER THE ISLANDS BOTH SATURDAY AND SUNDAY...WITH PARTIAL CLEARING AT NIGHT. THE TROUGH AXIS WILL MEANDER IN CONNECTION WITH THE MEANDERING LOW ALOFT TO THE N AS WE HEAD INTO NEXT WEEK...AND DETAILS ON THE LOW LEVEL WIND DIRECTION ARE UNCERTAIN...BUT CONFIDENCE IS HIGH THAT WINDS WILL REMAIN LIGHT OVER THE ISLANDS...AND A CONTINUATION OF THE DIURNAL CONVECTIVE WEATHER PATTERN IS EXPECTED TO CONTINUE INTO NEXT WEEK. THERE ARE SOME MINOR DIFFERENCES AMONG THE MODELS ABOUT HOW UNSTABLE IT WILL BE AFTER SUNDAY HOWEVER. IT APPEARS RIGHT NOW AS THOUGH THE MID LEVELS OF THE ATMOSPHERE WILL STAY A LITTLE TOO WARM TO SUPPORT THUNDERSHOWERS...THOUGH IF THESE WERE TO OCCUR THE BEST CHANCE WOULD BE OVER THE LEEWARD SLOPES AND INTERIOR PORTIONS OF THE BIG ISLAND EACH AFTERNOON THIS WEEKEND. IN OTHER AREAS...LOCALIZED DOWNPOURS ARE POSSIBLE... PARTICULARLY IN THE AFTERNOONS. && .AVIATION... CLOUDS AND SHRA OVER WINDWARD AREAS WILL BRING TEMPO MVFR AND ISOL IFR CONDITIONS...AND ISOL MVFR OVER LEEWARD WATERS. TRADE WINDS WILL DECREASE THROUGH TONIGHT AND TOMORROW WITH SEA BREEZES EXPECTED OVER LEEWARD LOCATIONS IN THE AFTERNOON. CLOUDS AND SHRA WILL INCREASE OVER INTERIOR SECTIONS SATURDAY AFTERNOON. && .MARINE... WITH TRADE WINDS DIMINISHING...THE SMALL CRAFT ADVISORY /SCA/ FOR WINDIER MARINE ZONES AROUND MAUI AND THE BIG ISLAND WAS ALLOWED TO EXPIRE A SHORT WHILE AGO. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA UNTIL AT LEAST THE MIDDLE OF NEXT WEEK. BIGGEST MARINE HIGHLIGHT IS THE HIGH SURF ALONG S FACING SHORES OF ALL ISLANDS...WITH A HIGH SURF ADVISORY IN EFFECT THROUGH THE WEEKEND. HOWEVER...A SERIES OF S SWELLS WILL KEEP ELEVATED SURF ALONG S FACING SHORES THROUGH MOST OF THE UPCOMING WEEK. A SMALL NW SWELL IS EXPECTED THIS WEEKEND...WITH A MODERATE NW SWELL BUILDING TUESDAY AND PEAKING WEDNESDAY. && .HFO WATCHES/WARNINGS/ADVISORIES... HIGH SURF ADVISORY UNTIL 6 PM HST SUNDAY FOR SOUTH FACING SHORES OF NIIHAU KAUAI OAHU MOLOKAI MAUI AND THE BIG ISLAND. && $$ DISCUSSION/MARINE...BIRCHARD AVIATION...MORRISON Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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