| Current Conditions | ||
| Temp |  | 10.8 C |
| RH | | 13 % |
| Wind | | SSE 15 mph |
| Road | | Open |
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Hawaiian Islands Synoptic Discussion and Guidance 821 FXHW60 PHFO 251947 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 1000 AM HST FRI JUL 25 2014 .SYNOPSIS... TRADE WINDS WILL FOCUS SHOWERS MAINLY ACROSS WINDWARD AND MAUKA AREAS. AN INCREASE IN SHOWER ACTIVITY IS EXPECTED DURING THE WEEKEND. TRADES MAY ALSO STRENGTHEN EARLY NEXT WEEK. && .DISCUSSION... WATER VAPOR IMAGERY SHOWS A MID/UPPER LEVEL HIGH OVER/JUST SOUTH OF THE STATE. AN UPPER LEVEL TROUGH IS LOCATED FAR TO THE NORTHWEST... WITH A 50 KT WEST-SOUTHWESTERLY JET AHEAD OF IT JUST APPROACHING KAUAI. AT THE SURFACE...HIGH PRESSURE IS LOCATED FAR NORTH-NORTHEAST OF THE STATE. 12Z SOUNDINGS FROM HILO AND LIHUE SHOW WELL DEFINED INVERSIONS NEAR 6KFT. PRECIPITABLE WATERS AROUND 1 1/3 INCHES ARE NEAR NORMAL FOR THIS TIME OF YEAR. EARLY MORNING MIMIC TOTAL PRECIPITABLE WATER IMAGERY SHOWS A POCKET OF DRIER AIR ACROSS THE CENTRAL ISLANDS AND JUST EAST OF THE BIG ISLAND...WITH A LARGER AREA OF MOISTURE ABOUT 200-300 MILES SOUTHEAST AND EAST OF THE BIG ISLAND. SHOWERS HAVE BEEN SOMEWHAT LIMITED OVERNIGHT DUE TO THE DRIER AND MORE STABLE AIR. KAUAI WAS SLIGHTLY WETTER THAN THE REST OF THE STATE DUE TO A POCKET OF MOISTURE CURRENT PASSING OVER THEM. A DRYING TREND WITH IMPROVING CONDITIONS IS EXPECTED AGAIN THIS AFTERNOON...SIMILAR TO THE TREND WE SAW YESTERDAY. TRADE WINDS WILL BE LESS BREEZY THAN THE PAST COUPLE DAYS. THE SURFACE HIGH FAR TO THE NORTHEAST HAS WEAKENED...AND SURFACE PRESSURES ACROSS THE ISLANDS HAVE DROPPED ABOUT 1-2MB OVER THE PAST 24 HOURS. TRADES SHOULD REMAIN IN THE GENERAL MODERATE CATEGORY THROUGH THE WEEKEND. THE AREA OF MOISTURE SOUTHEAST AND EAST OF THE BIG ISLAND WILL MOVE STEADILY WESTWARD. GFS 850-700MB RELATIVE HUMIDITY DOES A REASONABLE JOB DEPICTING THIS AREA...AND BRINGS IT TO THE BIG ISLAND EARLY SATURDAY. BOTH GFS AND ECMWF ARE RELATIVELY SIMILAR WITH THIS TIMING. AT THE SAME TIME...THE UPPER TROUGH NORTHWEST OF THE STATE WILL MOVE EASTWARD NORTH OF THE AREA. 12Z MODELS SHOW THE TROUGH PASSING JUST NORTH OF KAUAI ON SUNDAY BEFORE SLOWING AND WEAKENING. THE CURRENT FORECAST HAS AN INCREASE IN RAINFALL CHANCES THIS WEEKEND FROM EAST TO WEST BEGINNING NEAR THE BIG ISLAND LATE TONIGHT. MOST SHOWERS WILL BE FOCUSED ACROSS WINDWARD AND MAUKA AREAS...BUT SOME WILL SPREAD LEEWARD AS WELL. THE INCREASE IN MOISTURE AND RISE IN INVERSION HEIGHT COULD LEAD TO BRIEF HEAVIER SHOWERS...BUT WITH PERSISTENT MODERATE TRADES WE DO NOT EXPECT ANY HEAVY SHOWERS TO BECOME ANCHORED. DURING THE FIRST HALF OF NEXT WEEK...THE HIGH NORTHEAST OF THE STATE WEAKENS...BUT A POTENTIAL SYSTEM PASSING FAR SOUTH OF THE STATE COULD ENHANCE THE GRADIENT ACROSS THE ISLANDS. THIS MAY LEAD TO AN INCREASE IN WINDS STARTING AS EARLY AS SUNDAY NIGHT. 12Z MODELS HAVE BACKED OFF ON A SURGE OF TROPICAL MOISTURE THAT HAD BEEN ADVERTISED TO SPREAD ACROSS THE STATE DURING THE MID-WEEK TIME FRAME. THE 12Z GFS INSTEAD BRINGS SOME MOISTURE JUST AS FAR NORTH AS THE BIG ISLAND WEDNESDAY/THURSDAY. SPECIFICS ABOUT ANY INCREASE IN SHOWERS DURING MID TO LATE WEEK REMAIN UNCERTAIN. && .AVIATION... VFR CONDITIONS WILL PREDOMINATE ALL AREAS TODAY. ISOL MVFR CONDS ARE POSSIBLE IN PASSING TRADE WIND SHOWERS BUT SHOULD REMAIN LIMITED TO WINDWARD SLOPES AND NOT AFFECT TERMINAL LOCATIONS. GUSTY TRADE WINDS ALONG EXPOSED AND THROUGH CHANNELED AREAS ARE EXPECTED ONCE AGAIN THIS AFTERNOON BUT THE PRESSURE GRADIENT ACROSS THE ISLANDS IS SLACKENING SO INTENSITIES SHOULD BE NOTABLY LOWER THAN THE LAST COUPLE DAYS. && .MARINE... WINDS MAY INCREASE TO SMALL CRAFT ADVISORY LEVELS AS EARLY AS SUNDAY NIGHT FOR THE TYPICALLY WINDIER AREAS NEAR MAUI AND THE BIG ISLAND. EVEN AS THE SURFACE HIGH FAR NORTHEAST OF THE STATE WEAKENS SLIGHTLY...A POTENTIAL SYSTEM PASSING FAR SOUTH OF THE AREA COULD ENHANCE THE GRADIENT ACROSS THE ISLANDS. SMALL CRAFT ADVISORY WINDS ARE THEN POSSIBLE FOR THOSE AREAS THROUGH MUCH OF THE NEW WEEK. NO SIGNIFICANT SWELLS ARE EXPECTED THROUGH THE NEXT SEVERAL DAYS. SMALL LONG-PERIOD BACKGROUND SWELL FROM THE SSW AND SHORT-PERIOD SWELL FROM THE SE REPRESENT THE SWELL SOURCES FROM THE SOUTHERN HEMISPHERE...WHILE SHORT PERIOD WIND WAVES FROM THE EAST REPRESENT THE ONLY SOURCE OF SWELL FROM THE NORTHERN HEMISPHERE. && .HFO WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION/MARINE...BRAVENDER AVIATION...BEDAL Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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