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| Temp |  | 1.2 C |
| RH | | 87 % |
| Wind | | SSE 15 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 163 FXHW60 PHFO 011359 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 359 AM HST FRI AUG 1 2014 .SYNOPSIS... HIGH PRESSURE FAR NORTH OF THE STATE WILL KEEP TRADE WINDS BLOWING THROUGH THE WEEKEND AND INTO NEXT WEEK. ENHANCED MOISTURE MOVING FROM EAST TO WEST ACROSS THE ISLANDS TODAY THROUGH SATURDAY WILL RESULT IN AN INCREASE IN SHOWERS...WITH LOCALLY HEAVY RAINFALL POSSIBLE. DRIER AND MORE STABLE WEATHER IS EXPECTED FROM SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. && .DISCUSSION... SHOWERS HAVE REMAINED SCATTERED AT MOST ACROSS WINDWARD SECTIONS DURING THE NIGHT...WITH RAIN GAUGE DATA SHOWING ONLY SPARSE ACCUMULATIONS AT A FEW SITES. THERE IS AN AREA OF INCREASING SHOWER COVERAGE BEYOND 40 MILES SOUTHEAST OF THE BIG ISLAND. SURFACE ANALYSIS DEPICTS AN ELONGATED HIGH PRESSURE RIDGE OVER THE NORTHEAST PACIFIC OCEAN...AND THE REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE CENTERED ABOUT 500 MILES SOUTH SOUTHEAST OF HILO. MODERATE TO LOCALLY BREEZY TRADE WINDS PREVAIL ACROSS THE STATE. MIMIC-TPW SATELLITE IMAGERY INDICATES A SIGNIFICANT MOISTURE GRADIENT OVER THE AREA...WITH ESTIMATED PWATS OVER 2 INCHES BETWEEN 150W AND THE BIG ISLAND...RANGING DOWN TO AROUND 1.4 INCHES FROM OAHU TO KAUAI. THE 12Z SOUNDINGS INDICATE THIS MOISTURE GRADIENT AS WELL. THE INVERSION AT HILO HAS RISEN TO OVER 8000 FEET...BUT REMAINS NEAR 7000 FEET AT LIHUE. ALOFT... A WEAK MID/UPPER LEVEL TROUGH EXTENDS FROM NEAR 30N160W SOUTHWARD TO THE WEST OF KAUAI...AND A MID LEVEL RIDGE AXIS EXTENDS WESTWARD ALONG 20N TO NEAR THE BIG ISLAND. THE BAND OF DEEP TROPICAL MOISTURE INITIALLY JUST EAST OF THE BIG ISLAND WILL CONTINUE MOVING WESTWARD ACROSS THE STATE FROM TODAY THROUGH SATURDAY. THIS TROPICAL MOISTURE SHOULD PEAK THIS AFTERNOON AND EVENING ACROSS THE BIG ISLAND...THEN LATE TONIGHT THROUGH SATURDAY MORNING ACROSS THE SMALLER ISLANDS. MODERATE INSTABILITY WILL BE IN PLACE...BUT THE RISK FOR THUNDERSTORMS WOULD SEEM TO BE QUITE LOW DUE TO RELATIVELY WARM MID LEVEL TEMPERATURES AND A LACK OF DEEP FORCING. WITH ONLY A WEAK UPPER TROUGH LIFTING OUT TO OUR WEST AND NORTH DURING THIS TIME...IT APPEARS THAT THIS WILL PROBABLY BE MORE OF AN OROGRAPHICALLY DRIVEN EVENT WITH LOCALLY HEAVY RAINS MOST LIKELY ON THE WINDWARD AREAS...IN CONTRAST TO THE MORE WIDESPREAD HEAVY RAINS AND THUNDERSTORMS THAT WERE OBSERVED A COUPLE OF WEEKS AGO WHEN A PREVIOUS BOUT OF TROPICAL MOISTURE MOVED THROUGH THE STATE. THE FLASH FLOODING THREAT APPEARS TO BE LOW...BUT WOULD NOT BE SURPRISED TO SEE SOME FLOOD ADVISORIES ISSUED FROM LATER TODAY THROUGH SATURDAY. FOR THE FORECAST...HAVE INCLUDED THE MENTION OF LOCALLY HEAVY RAIN FOR THE BIG ISLAND AND WINDWARD MAUI TODAY...SPREADING WESTWARD TO OAHU THIS EVENING... KAUAI LATE TONIGHT...AND STATEWIDE SATURDAY MORNING. THE MOISTURE PLUME SHOULD CONTINUE MOVING WESTWARD SATURDAY...WITH THE HEAVY RAIN THREAT DIMINISHING FOR ALL AREAS EXCEPT KAUAI COUNTY BY AFTERNOON. A GRADUAL DRYING TREND IS EXPECTED FOR SATURDAY NIGHT THROUGH SUNDAY...THEN A RATHER DRY MODERATE TRADE WIND PATTERN SHOULD PREVAIL FROM MONDAY THROUGH AT LEAST THE MIDDLE OF NEXT WEEK... WITH GENERALLY BELOW NORMAL PWATS AND RATHER STRONG RIDGING ALOFT PREVAILING. WOULD EXPECT LIMITED TRADE SHOWERS ACROSS WINDWARD AND MAUKA AREAS...MAINLY DURING THE NIGHT AND EARLY MORNING HOURS... WITH MOSTLY CLEAR AND DRY CONDITIONS LEEWARD. LOOKING FURTHER AHEAD TOWARD THURSDAY AND FRIDAY OF NEXT WEEK... THE 00Z MODEL SUITE...AS HAS BEEN THE CASE FOR THE PAST SEVERAL CYCLES...BRINGS YET ANOTHER SURGE OF DEEP TROPICAL MOISTURE TOWARD THE STATE FROM THE EAST. THIS MOISTURE APPEARS TO BE ASSOCIATED WITH THE MODEL DEPICTION OF CURRENT EAST PACIFIC TROPICAL STORM ISELLE. IT IS HIGHLY UNCERTAIN AT THIS POINT WHETHER REMNANTS OF THIS SYSTEM WILL MAKE IT TO THE VICINITY OF HAWAII...BUT THERE IS SOME POTENTIAL FOR ANOTHER BOUT OF WET WEATHER TOWARD THE END OF NEXT WEEK. && .AVIATION... INCREASING TROPICAL MOISTURE IS NOW ARRIVING ALONG THE WINDWARD BIG ISLAND. THE ARRIVAL OF THIS ENHANCED MOISTURE WILL PRODUCE ABUNDANT LOW CLOUDS AND SHOWERS WITH LOWER CEILINGS AND REDUCED VISIBILITIES. THESE CONDITIONS WILL REQUIRE THE CONTINUATION OF AIRMET SIERRA FOR MOUNTAIN OBSCURATION ALONG THE WINDWARD FACING TERRAIN OF THE BIG ISLAND THROUGH MOST OF THE DAY. AS THIS ENHANCED TROPICAL MOISTURE CONTINUES TO ADVECT WESTWARD...THESE LOWER CEILINGS AND REDUCED VISIBILITIES WILL ALSO LIKELY SPREAD TO PARTS OF WINDWARD MAUI LATER THIS MORNING...SO EXPECT PORTIONS OF MAUI TO BE ADDED TO AIRMET SIERRA IN THE NEAR FUTURE. WEST OF MAUI...VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST LEEWARD SECTIONS OF THE OTHER SMALLER ISLANDS THIS MORNING...WITH BRIEF MVFR CONDITIONS DEVELOPING ALONG WINDWARD FACING SLOPES AND THE HIGHER TERRAIN ON MOST OF THESE ISLANDS. LATER IN THE DAY... THERE IS A GOOD CHANCE MOUNTAIN OBSCURATION MAY EVENTUALLY DEVELOP WEST OF MAUI...SO AIRMET SIERRA MAY ALSO BE REQUIRED FOR ADDITIONAL PARTS OF THE STATE. AS A RESULT OF THE MODERATE TO LOCALLY BREEZY LOW-LEVEL TRADE WIND FLOW...AIRMET TANGO REMAINS IN EFFECT FOR LOW-LEVEL TURBULENCE BELOW 7 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 TONIGHT. && .MARINE... AN 0738Z ASCAT PASS ACROSS THE FAR WESTERN HAWAIIAN COASTAL WATERS FOUND SOME 20 KNOT WINDS IN THE KAUAI CHANNEL. THE PASS MISSED THE EASTERN WATERS AROUND MAUI COUNTY AND THE BIG ISLAND...BUT RECENT HIGH RESOLUTION WRF MODEL DATA SUGGEST THAT 25 KNOT WINDS ARE QUITE POSSIBLE IN THAT AREA. WILL MAINTAIN THE EXISTING SMALL CRAFT ADVISORY THROUGH SUNDAY. MODERATE SSW SWELL WILL INCREASE SOMEWHAT THIS AFTERNOON...THEN A REINFORCING SOUTH SWELL SHOULD INCREASE SURF FURTHER ON SATURDAY...POSSIBLY APPROACHING OR REACHING MINIMAL ADVISORY LEVELS ON SOUTH FACING SHORES. THIS SURF EVENT SHOULD PEAK DURING SATURDAY THEN SLOWLY DECREASE SUNDAY THROUGH MONDAY. SURF WILL SEE A BUMP ON WEST FACING SHORES AS WELL DUE TO THE SSW DIRECTION. 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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