| Current Conditions | ||
| Temp |  | 3.0 C |
| RH | | 97 % |
| Wind | | SE 12 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 086 FXHW60 PHFO 020640 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 840 PM HST FRI AUG 1 2014 .SYNOPSIS... AN AREA OF DEEP TROPICAL MOISTURE WILL CONTINUE TO MOVE WESTWARD ACROSS THE STATE TONIGHT AND SATURDAY. NUMEROUS SHOWERS WILL AFFECT WINDWARD AREAS...WITH SOME SHOWERS SPILLING OVER INTO LEEWARD SECTIONS AS WELL. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE TONIGHT AND SATURDAY. DRIER AND MORE STABLE TRADE WIND WEATHER IS EXPECTED SUNDAY THROUGH WEDNESDAY. ANOTHER BOUT OF WET WEATHER IS POSSIBLE LATE NEXT WEEK. && .DISCUSSION... A WET EVENING IS IN PROGRESS ACROSS THE BIG ISLAND OF HAWAII... WITH RADAR LOOPS SHOWING WIDESPREAD SHOWER ACTIVITY ACROSS THAT AREA. A FLOOD ADVISORY WAS RECENTLY ISSUED FOR PARTS OF THE HAMAKUA COAST. SHOWERS ARE ALSO INCREASING ACROSS THE ALENUIHAHA CHANNEL AND EAST MAUI. FURTHER WEST...LIGHTER SHOWERS ARE MOVING OVER WINDWARD OAHU...WHILE ACTIVITY REMAINS SPARSE OVER KAUAI. THERE WERE A COUPLE OF THUNDERSTORMS DURING THE LATE AFTERNOON ACROSS THE BIG ISLAND INTERIOR...BUT THESE DIED DOWN BEFORE SUNSET. MIMIC-TPW SATELLITE IMAGERY CLEARLY SHOWS THE SURGE OF DEEP TROPICAL MOISTURE MOVING WESTWARD ACROSS THE STATE...WITH ESTIMATED PWATS OVER 2 INCHES EXTENDING FROM JUST NORTH OF THE BIG ISLAND AND MAUI SOUTHWARD INTO THE DEEP TROPICS. THE 00Z SOUNDINGS DEPICTED A SHARP MOISTURE GRADIENT ACROSS THE STATE...WITH A MEASURED PWAT OF 2.21 INCHES AT HILO AND AND 1.36 INCHES AT LIHUE. THIS PWAT VALUE AT HILO IS MORE THAN 3 STANDARD DEVIATIONS ABOVE NORMAL. HILO ALSO SHOWED A MOIST ADIABATIC PROFILE WITH NO INVERSION PRESENT...WHILE AN INVERSION BASED NEAR 7000 FEET PERSISTED AT LIHUE. AT THE SURFACE...MODERATE TRADES CONTINUE ACROSS THE STATE...BETWEEN HIGH PRESSURE TO OUR NORTHEAST AND THE REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE TO OUR SOUTH. ALOFT...WATER VAPOR IMAGERY DEPICTS A WEAK UPPER LEVEL TROUGH SLIDING EASTWARD SEVERAL HUNDRED MILES NORTH OF THE STATE...WITH A MID LEVEL RIDGE EXTENDING WEST ACROSS THE BIG ISLAND. THROUGH THE OVERNIGHT...EXPECT INCREASING SHOWERS AND LOCALLY HEAVY RAINFALL TO CONTINUE SPREADING WESTWARD ACROSS THE STATE. WITH ONLY MODEST INSTABILITY IN PLACE (500 MB TEMPS OF -6C AND NEARLY MOIST ADIABATIC PROFILES) AND LITTLE UPPER SUPPORT EVIDENT...WOULD EXPECT THIS TO BE MAINLY AN OROGRAPHICALLY DRIVEN EVENT WITH THE HEAVIEST RAINS FAVORING MAINLY WINDWARD AREAS. HOWEVER...ISOLATED HEAVY DOWNPOURS WILL BE POSSIBLE OVER LEEWARD AREAS AS WELL. POTENTIAL FOR THUNDERSTORMS SHOULD REMAIN LOW...BUT AN ISOLATED STORM IS NOT TOTALLY OUT OF THE QUESTION. THE EXISTING FORECAST APPEARS TO HAVE A GOOD HANDLE ON THE EXPECTED EVOLUTION...AND NO UPDATES ARE CURRENTLY PLANNED FOR THIS EVENING. FREQUENT WINDWARD SHOWERS AND LOCALLY HEAVY RAINS WILL CONTINUE ACROSS THE STATE INTO SATURDAY MORNING...WITH THE FOCUS OF ACTIVITY SHIFTING FURTHER WESTWARD ACROSS THE SMALLER ISLANDS DURING THE DAY. RAIN CHANCES SHOULD DECREASE SOMEWHAT BY AFTERNOON...WITH THE HEAVY RAIN THREAT DIMINISHING AS THE AREA OF HIGHEST TROPICAL MOISTURE PASSES WEST OF KAUAI. SATURDAY NIGHT AND SUNDAY SHOULD SEE A DRYING TREND WITH DECREASING DEWPOINTS AS A MUCH DRIER AIRMASS MOVES IN FROM THE EAST. A DRY/STABLE TRADE WIND PATTERN IS EXPECTED FOR MONDAY THROUGH WEDNESDAY...WITH RIDGING ALOFT AND BELOW NORMAL PWATS KEEPING SHOWER ACTIVITY SOMEWHAT SPARSE AND MAINLY CONFINED TO WINDWARD AREAS. LOOKING FURTHER AHEAD TOWARD THURSDAY AND FRIDAY OF NEXT WEEK... FOR THE PAST SEVERAL CYCLES NOW GLOBAL MODELS HAVE CONSISTENTLY BROUGHT YET ANOTHER SURGE OF DEEP TROPICAL MOISTURE TOWARD THE STATE FROM THE EAST. THIS MOISTURE IS ASSOCIATED WITH THE MODEL DEPICTION OF CURRENT EAST PACIFIC TROPICAL STORM ISELLE. IT REMAINS HIGHLY UNCERTAIN AT THIS POINT WHETHER ISELLE OR ITS REMNANTS WILL EVENTUALLY REACH THE VICINITY OF HAWAII...BUT THERE IS THE POTENTIAL FOR ANOTHER BOUT OF WET WEATHER TOWARD THE END OF NEXT WEEK. STAY TUNED FOR FORECAST UPDATES DURING THE NEXT SEVERAL DAYS. && .AVIATION... TROPICAL MOISTURE CONTINUES TO SPREAD WESTWARD ACROSS THE MAIN HAWAIIAN ISLANDS THIS EVENING. SO FAR...THIS MOIST AIR MASS HAS PRODUCED ABUNDANT LOW CLOUDS AND SHOWERS WITH LOWER CEILINGS AND REDUCED VISIBILITIES OVER THE WINDWARD SECTIONS AND HIGHER TERRAIN OF THE BIG ISLAND...MAUI AND MOLOKAI. THERE WERE ALSO THUNDERSTORMS OVER THE BIG ISLAND SUMMITS RECENTLY...BUT THESE COLLAPSED BEFORE SUNSET. AIRMET SIERRA REMAINS IN EFFECT FOR MOUNTAIN OBSCURATION ON THE ISLANDS. THIS AIRMET WILL LIKELY REMAIN IN EFFECT FOR THESE LOCATIONS THROUGH TONIGHT. WEST OF MOLOKAI...VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST LEEWARD SECTIONS OF OAHU AND KAUAI. HOWEVER...MVFR CONDITIONS WILL LIKELY AFFECT WINDWARD FACING SLOPES AND THE HIGHER TERRAIN ON BOTH OF THESE ISLANDS TONIGHT. IN FACT...MOUNTAIN OBSCURATION MAY EVENTUALLY DEVELOP ON OAHU AND KAUAI...SO AIRMET SIERRA MAY BE REQUIRED FOR ADDITIONAL PARTS OF THE STATE LATER TONIGHT OR EARLY SATURDAY MORNING. AS A RESULT OF THE MODERATE TO LOCALLY BREEZY LOW-LEVEL TRADE WIND FLOW...AIRMET TANGO REMAINS IN EFFECT FOR LOW-LEVEL TURBULENCE BELOW 8 KFT IMMEDIATELY SOUTH THROUGH WEST OF THE HIGHER TERRAIN ON ALL ISLANDS. BASED ON THE LATEST GUIDANCE...THIS AIRMET WILL LIKELY REMAIN IN EFFECT THROUGH SATURDAY. && .MARINE... A 2006Z ASCAT PASS CLIPPED THE FAR WESTERN EDGE OF THE HAWAIIAN COASTAL WATERS...AND FOUND WINDS ONLY NEAR 15 KNOTS IN THE WATERS AROUND KAUAI. THERE IS A MODERATE PRESSURE GRADIENT IN PLACE ACROSS THE AREA BETWEEN HIGH PRESSURE TO THE NORTH AND THE REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE TO THE SOUTH...AND WILL MAINTAIN THE EXISTING SMALL CRAFT ADVISORY FOR THE TYPICALLY WINDY WATERS AROUND MAUI COUNTY AND THE BIG ISLAND. HOPEFULLY THE OVERNIGHT ASCAT PASS WILL PROVIDE ADDITIONAL WIND DATA ACROSS THE ADVISORY AREA. INCREASING SSW SWELL IS EXPECTED TONIGHT AND SATURDAY WITH SURF APPROACHING ADVISORY LEVELS ON SOUTH FACING SHORES. THIS SURF EVENT WILL SLOWLY DECREASE SUNDAY THROUGH MONDAY. SURF WILL SEE A SLIGHT BUMP ON WEST FACING SHORES AS WELL DUE TO THE SSW DIRECTION. LOW END SOUTH SWELL WILL MAINTAIN BACKGROUND SURF ALONG SOUTH SHORES TUESDAY AND WEDNESDAY. OTHERWISE...PREVAILING TRADE WINDS WILL CONTINUE TO PRODUCE SHORT PERIOD SWELL AND CHOPPY NEAR AVERAGE SURF ALONG EAST FACING SHORES THROUGH THE NEXT SEVERAL DAYS. && .HFO WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR MAALAEA BAY- PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS. && $$ DISCUSSION/MARINE...JACOBSON AVIATION...HOUSTON Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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