| Current Conditions | ||
| Temp |  | 0.1 C |
| RH | | 22 % |
| Wind | | WSW 16 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 400 FXHW60 PHFO 181406 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 405 AM HST SAT MAY 18 2013 .SYNOPSIS... TRADE WINDS WILL WEAKEN TODAY...AND TURN TOWARD THE NORTH ON KAUAI AND OAHU...AS A TROUGH DEVELOPS NEAR THE ISLANDS. THE TROUGH WILL MOVE SLOWLY EAST THIS WEEKEND...AND LIGHT TO MODERATE NORTHERLY WINDS WILL SPREAD TO MAUI COUNTY...WHILE LIGHT SOUTH WINDS WILL PREVAIL NEAR THE BIG ISLAND. WITH LIGHT WINDS...CLOUDS AND SHOWERS WILL FAVOR AFTERNOON HOURS...AND WILL PRIMARILY AFFECT LEEWARD AREAS. THE PRESENCE OF THE TROUGH WILL HELP TO INTENSIFY ANY SHOWERS THAT FORM OVER THE ISLANDS THE NEXT SEVERAL DAYS. && .DISCUSSION... A SOMEWHAT UNSEASONABLE WEATHER PATTERN...AND LOW CONFIDENCE FORECAST...ARE IN THE WORKS FOR THE NEXT COUPLE OF DAYS. CURRENTLY...WATER VAPOR IMAGERY SHOWS A WEAKENING LOW ALOFT MOVING SLOWLY ESE JUST N OF MAUI COUNTY...WITH THE LOW BECOMING INCREASINGLY ILL-DEFINED OVER THE PAST FEW HOURS. AT THE SURFACE...A WEAKENING TRADE WIND FLOW IS BEING SUPPORTED BY A SURFACE HIGH ABOUT 1550 MILES NE OF THE ISLANDS...BUT THE LATEST SURFACE ANALYSIS PLACES A SHARPENING SURFACE TROUGH NEAR MAUI COUNTY THAT WILL BECOME A PRIMARY PLAYER IN ISLAND WEATHER OVER THE NEXT SEVERAL DAYS. DESPITE WEAKENING...THE PRESENCE OF THE LOW ALOFT IS MAINTAINING A MODERATELY UNSTABLE AIRMASS OVER THE ISLANDS...AS SEEN IN EARLY MORNING SOUNDINGS...AND HIGHLIGHTED BY THE STRONG RADAR RETURNS EMANATING FROM SHOWERS. MEANWHILE...WATER VAPOR IMAGERY SHOWS A RAPIDLY SHARPENING TROUGH ALOFT N OF THE ISLANDS NEAR 30N 160W... WHICH WILL BE AN IMPORTANT PLAYER IN ISLAND WEATHER OVER THE NEXT SEVERAL DAYS. HAVE INTRODUCED A SLIGHT CHANCE OF THUNDERSTORMS OVER INTERIOR AND LEEWARD BIG ISLAND FOR THIS AFTERNOON...DUE TO THE INSTABILITY AND RECENT RADAR OBSERVATIONS. IN OTHER AREAS...LOCALIZED DOWNPOURS ARE POSSIBLE. THE FORECAST CALLS FOR THE WEAKENING UPPER LOW NEAR THE ISLANDS TO MOVE ESE BEFORE DISSIPATING E OF THE BIG ISLAND LATER TODAY...WHILE THE NEW TROUGH ALOFT DIGS AGGRESSIVELY SE OVER WATERS N AND NE OF THE ISLANDS. THIS STRONGLY DIGGING TROUGH WILL DEVELOP INTO A CLOSED LOW ALOFT BY SUNDAY...WITH THIS LOW THEN MEANDERING IN AN AREA ABOUT 550 MILES NE OF THE ISLANDS 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 NE OF THE ISLANDS IN RESPONSE TO THE DEVELOPING LOW ALOFT...WITH A SHARP SURFACE TROUGH EXTENDING SOUTHWARD OVER THE ISLANDS. THE TROUGH WILL INTERRUPT THE TRADE FLOW...AND TURN WINDS TO THE N AND NE OVER KAUAI AND OAHU BY TONIGHT...WHILE WINDS NEAR THE BIG ISLAND VEER TO THE S. AS THE TROUGH SLIDES E TONIGHT AND SUNDAY...THE LIGHT TO MODERATE N WINDS WILL SPREAD TO MAUI COUNTY...WITH THIS GENERAL WIND FLOW PERSISTING THROUGH MONDAY. ON TUESDAY THE SURFACE TROUGH OVER THE ISLANDS WILL WEAKEN...BUT LIGHT E TO ESE WINDS ARE EXPECTED TO PREVAIL STATEWIDE FOR MUCH OF NEXT WEEK...AS THE TROUGH LINGERS N OF THE ISLANDS. BIGGEST SHORT TERM FORECAST CHALLENGE HINGES ON THE STRENGTH AND AXIS OF THE DEVELOPING LOW LEVEL TROUGH IN RELATION TO THE ISLAND CHAIN. THIS WILL HAVE PROFOUND EFFECTS ON ISLAND WEATHER...AND CONFIDENCE IN THE DETAILS OF THE FORECAST OVER THE NEXT COUPLE OF DAYS ARE LOWER THAN NORMAL. THE ONGOING FORECAST IS CALLING FOR A LAND AND SEA BREEZE REGIME OVER THE ISLANDS...BUT WILL NEED TO BE FINE TUNED AS EVENTS UNFOLD...AS THE N/NE WINDS W OF THE TROUGH AXIS MAY BE STRONG ENOUGH TO OVERRIDE ISLAND-SCALE LAND/SEA BREEZE WINDS. && .AVIATION... CLOUDS AND SHRA OVER WINDWARD AREAS BRINGING TEMPO MVFR AND ISOL IFR CONDITIONS...AND ISOL MVFR OVER LEEWARD WATERS. WEAKENING TRADE WINDS TODAY WILL ALLOW WIDESPREAD SEA BREEZES OVER LEEWARD LOCATIONS IN THE AFTERNOON. CLOUDS AND SHRA WILL INCREASE OVER INTERIOR SECTIONS IN THE AFTERNOON. && .MARINE... WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA STATEWIDE THROUGH THE VALID TIME OF THE MARINE FORECAST. BIGGEST MARINE HIGHLIGHT IS THE HIGH SURF ALONG S FACING SHORES OF ALL ISLANDS...WITH A HIGH SURF ADVISORY IN EFFECT THROUGH THE WEEKEND. A MARINE WEATHER STATEMENT HAS BEEN ISSUED TO HIGHLIGHT THE THREAT TO THE BOATING COMMUNITY. 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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