| Current Conditions | ||
| Temp |  | 2.1 C |
| RH | | 95 % |
| Wind | | SSE 16 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 684 FXHW60 PHFO 010637 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 837 PM HST THU JUL 31 2014 .SYNOPSIS... HIGH PRESSURE FAR NORTH OF THE STATE WILL KEEP TRADE WINDS BLOWING THROUGH THE WEEKEND AND INTO NEXT WEEK. ENHANCED MOISTURE MOVING ACROSS THE ISLANDS FROM LATE TONIGHT THROUGH SATURDAY WILL RESULT IN AN INCREASE IN SHOWERS...WITH SOME LOCALLY HEAVY RAINFALL POSSIBLE. DRIER AND MORE STABLE WEATHER IS EXPECTED FROM SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. && .DISCUSSION... RADAR LOOPS AND RAIN GAUGE DATA INDICATE A MOSTLY DRY EVENING THUS FAR ACROSS THE HAWAIIAN ISLANDS...WITH LIGHT RAINFALL AMOUNTS OVER SOME WINDWARD AREAS. SURFACE ANALYSIS DEPICTS AN ELONGATED HIGH PRESSURE RIDGE IN ITS TYPICAL LOCATION OVER THE NORTHEAST PACIFIC OCEAN...AND THE REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE CENTERED ABOUT 520 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 OF UP TO 2 INCHES JUST SOUTHEAST OF THE BIG ISLAND...AND PWATS OF 1.3-1.5 INCHES FROM MAUI THROUGH KAUAI. THE 00Z SOUNDINGS INDICATE THIS MOISTURE GRADIENT AS WELL...ALONG WITH RELATIVELY WEAK INVERSIONS BASED NEAR 7000 FEET. 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. OVERNIGHT...THE LEADING AREA OF ENHANCED TROPICAL MOISTURE WILL CONTINUE SPREADING ACROSS THE BIG ISLAND AND MAUI. WHILE PWATS WILL BE WELL ABOVE NORMAL (1.5 TO 2 INCHES)...IT APPEARS THAT THE DEEPEST TROPICAL MOISTURE (PWATS GREATER THAN 2 INCHES) WILL REMAIN SOUTH OF THE BIG ISLAND DURING THE NIGHT. THERE SHOULD BE SUFFICIENT MOISTURE TO PRODUCE MORE WIDESPREAD SHOWERS ACROSS THE FAVORED WINDWARD AREAS LATE TONIGHT. IN THE EVENING FORECAST UPDATE...HAVE DELAYED THE TIMING OF HIGH POPS AND LOCALLY HEAVY RAINFALL FOR WINDWARD BIG ISLAND AND MAUI UNTIL LATE TONIGHT. FURTHER WEST FROM MOLOKAI THROUGH KAUAI...WOULD EXPECT A TYPICAL TRADE WIND PATTERN OVERNIGHT WITH SCATTERED MOSTLY LIGHT SHOWERS FAVORING THE LATE NIGHT HOURS. ON FRIDAY...ANOTHER BAND OF MORE SUBSTANTIAL TROPICAL MOISTURE WHICH IS CURRENTLY LOCATED NEAR 20N 150W WILL MOVE WESTWARD TOWARD THE BIG ISLAND. LOCALLY HEAVY RAINS WILL REMAIN POSSIBLE ACROSS THE EASTERN HALF OF THE STATE...WITH WINDWARD CLOUDS AND SHOWERS GENERALLY INCREASING STATEWIDE. TROPICAL MOISTURE SHOULD PEAK FRIDAY EVENING ACROSS THE BIG ISLAND...AND LATE FRIDAY NIGHT THROUGH SATURDAY MORNING ACROSS THE SMALLER ISLANDS. MODERATE INSTABILITY WILL BE IN PLACE...BUT THE RISK FOR THUNDERSTORMS WOULD STILL SEEM TO BE QUITE LOW DUE TO RELATIVELY WARM MID LEVEL TEMPERATURES. WITH NO UPPER TROUGH IN PLACE TO OUR WEST...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 DURING THE NEXT COUPLE OF DAYS. THE AREA OF ENHANCED MOISTURE WILL SHIFT WEST OF THE STATE SATURDAY NIGHT. A RATHER DRY MODERATE TRADE WIND PATTERN SHOULD THEN PREVAIL FROM SUNDAY THROUGH AT LEAST THE MIDDLE OF NEXT WEEK...WITH GENERALLY BELOW NORMAL PWATS AND RATHER STRONG RIDGING ALOFT PREVAILING. && .AVIATION... INCREASING TROPICAL MOISTURE IS MOVING INTO THE BIG ISLAND THIS EVENING FROM THE EAST...BRINGING INCREASED LOW CLOUDS AND SHOWERS THAT WILL PRODUCE REDUCED VISIBILITIES AND LOWER CEILINGS. IN ANTICIPATION OF THESE DETERIORATING CONDITIONS OVER THE WINDWARD BIG ISLAND...AIRMET SIERRA HAS BEEN ISSUED FOR MOUNTAIN OBSCURATION FROM UPOLU POINT TO CAPE KUMUKAHI TO SOUTH CAPE. ELSEWHERE...VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST OF THE SMALLER ISLANDS TONIGHT...WITH BRIEF MVFR CONDITIONS POSSIBLE ALONG WINDWARD FACING SLOPES OF THESE ISLANDS...ESPECIALLY AFTER MIDNIGHT HST. 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. THIS AIRMET WILL LIKELY REMAIN IN EFFECT AT LEAST THROUGH FRIDAY AFTERNOON. && .MARINE... A 2027Z ASCAT PASS DID NOT FIND ANY 25 KNOT WINDS ACROSS THE EASTERN HALF OF THE HAWAIIAN COASTAL WATERS. HOWEVER IT IS POSSIBLE THAT THE PRESSURE GRADIENT OVER THE AREA HAS TIGHTENED SOMEWHAT SINCE THEN...AS THE REMNANT LOW OF FORMER TROPICAL DEPRESSION GENEVIEVE MOVES WESTWARD TOWARD ITS CLOSEST APPROACH POINT WELL TO THE SOUTH OF THE BIG ISLAND. WILL MAINTAIN THE EXISTING SMALL CRAFT ADVISORY FOR THE TYPICALLY WINDIER AREAS AROUND MAUI COUNTY AND BIG ISLAND. MODERATE SOUTH SWELL AND SURF WILL CONTINUE ON SOUTH FACING SHORES THROUGH FRIDAY...THEN A REINFORCING SOUTH SWELL SHOULD INCREASE SURF FURTHER ON SATURDAY...POSSIBLY APPROACHING ADVISORY LEVELS. THIS SURF EVENT SHOULD PEAK LATER SATURDAY THEN SLOWLY DECREASE SUNDAY THROUGH MONDAY. OTHERWISE...PREVAILING TRADE WINDS WILL CONTINUE TO PRODUCE SHORT PERIOD SWELL AND CHOPPY 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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