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Hawaiian Islands Synoptic Discussion and Guidance

610
FXHW60 PHFO 160630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST MON SEP 15 2014

.SYNOPSIS...
MUGGY CONDITIONS WILL CONTINUE THROUGH THE REST OF THIS WEEK.
LIGHT TRADE WINDS WILL PREVAIL THROUGH WEDNESDAY...BUT WILL STILL
ALLOW FOR LOCALIZED AFTERNOON SEA BREEZES AND INTERIOR CLOUDS AND
SHOWERS. THE LIGHT TRADES ARE FORECAST TO BREAK DOWN AGAIN LATE
THIS WEEK...LEADING TO MORE WIDESPREAD SEA BREEZES AND AFTERNOON
CLOUDS AND SHOWERS.

&&

.DISCUSSION...
SHOWERS ACROSS THE INTERIOR BIG ISLAND DIED OFF QUICKLY EARLY
THIS EVENING WITH LOSS OF DAYTIME HEATING. CURRENTLY RADAR DETECTS
SCATTERED SHOWERS EAST OF THE BIG ISLAND...WITH ISOLATED SHOWERS
DOTTING THE COASTAL WATERS ELSEWHERE. RAIN GAUGE DATA SHOW
ISOLATED MOSTLY LIGHT AMOUNTS DURING THE LATE AFTERNOON...WITH A
COUPLE OF HEAVIER TOTALS ON THE BIG ISLAND AT MAUNA LOA AND AT
KAHUKU RANCH. SURFACE ANALYSIS DEPICTS LOW PRESSURE CENTERED FAR
NORTHEAST OF THE STATE...WITH A TRAILING COLD FRONT/TROUGH
EXTENDING SW TO NEAR THE BIG ISLAND. MIMIC-TPW IMAGERY ALSO
CLEARLY SHOWS A STRIPE OF HIGHER PRECIPITABLE WATER VALUES ALONG
THE FRONT/TROUGH...ALTHOUGH THE MIMIC ESTIMATED VALUES ARE
RUNNING A BIT HIGH COMPARED TO THE MEASURED 00Z HILO PWAT OF 1.69
INCHES. A DRIER AIRMASS IS SPREADING INTO THE STATE FROM THE NORTH
BEHIND THE TROUGH...AS SHOWN BY THE 00Z LIHUE SOUNDING WHERE PWAT
DROPPED OFF TO 1.35 INCHES...A DECREASE OF 4/10 OF AN INCH DURING
THE PREVIOUS 12 HOURS. A 1023 MB SURFACE HIGH CENTERED FAR
NORTHWEST OF THE STATE IS BUILDING EASTWARD BEHIND THE FRONT/TROUGH...
ALLOWING LIGHT TRADES TO RESUME OVER THE ISLANDS. ALOFT...A WEAK
UPPER LEVEL TROUGH LIES ACROSS THE STATE...WITH A LARGE DEEP
LAYERED ANTICYCLONE CENTERED WELL TO OUR NORTHWEST...JUST TO THE
EAST OF THE DATELINE.

OVERNIGHT...DRY CONDITIONS SHOULD PREVAIL ACROSS MOST AREAS AS A
SOMEWHAT DRIER AIRMASS CONTINUES TO SPREAD SOUTHWARD ACROSS THE
STATE...AND THE WEAKENING LOW PRESSURE TROUGH SETTLES SOUTH OF THE
BIG ISLAND TAKING THE STRIPE OF HIGHER MOISTURE WITH IT. MAY NEED
TO DO SOME MINOR UPDATES TO THE GRIDDED/TEXT FORECASTS TO REFLECT
CURRENT RADAR TRENDS...BUT NO MAJOR CHANGES ARE PLANNED.

SURFACE HIGH PRESSURE WILL BUILD SLOWLY EASTWARD TO THE NORTH OF
THE STATE DURING THE NEXT COUPLE OF DAYS...MAINTAINING A LIGHT
BACKGROUND TRADE WIND FLOW. TRADES WILL REMAIN LIGHT ENOUGH TO
ALLOW LOCALIZED SEA BREEZES TO DEVELOP EACH AFTERNOON. THEREFORE
WE WOULD EXPECT A HYBRID PATTERN...WITH SHOWERS AND CLOUDS
FOCUSING ON WINDWARD SLOPES DURING THE NIGHTS...AND ACROSS SOME OF
THE LEEWARD AND INTERIOR AREAS DURING THE AFTERNOONS. AVAILABLE
MOISTURE SHOULD REMAIN NEAR TO SLIGHTLY BELOW NORMAL...SO WOULD
EXPECT MOST RAINFALL AMOUNTS TO REMAIN LIGHT. WITH OCEAN WATERS TO
THE NORTH OF THE STATE SIGNIFICANTLY WARMER THAN NORMAL...RATHER
MUGGY CONDITIONS ARE LIKELY TO CONTINUE DESPITE THE LIGHT TRADE
FLOW.

FROM THURSDAY INTO THE WEEKEND...ANOTHER COLD FRONT IS FORECAST
TO DROP SOUTHWARD ACROSS THE NORTH CENTRAL PACIFIC. THIS WILL
LIKELY PUSH THE SUBTROPICAL RIDGE SOUTH AND EAST...DISRUPTING
THE PRESSURE GRADIENT ACROSS THE STATE. LOCAL TRADE WIND FLOW
SHOULD WEAKEN FURTHER OR DISAPPEAR ENTIRELY DURING THIS TIME...
ALLOWING FOR ANOTHER PERIOD OF MORE WIDESPREAD DAYTIME SEA BREEZES
AND NIGHTTIME LAND BREEZES. WITH MORE OF A PURE CONVECTIVE
PATTERN...WE SHOULD SEE MORE PREVALENT INTERIOR CLOUDS AND SHOWERS
DURING EACH AFTERNOON...AND MORE CLEARING ACROSS THE ISLANDS EACH
NIGHT. MODEL CONSENSUS EVENTUALLY STALLS THE FRONTAL BOUNDARY
A COUPLE HUNDRED MILES NORTH OF THE STATE BY THE END OF THE
WEEKEND AND INTO EARLY NEXT WEEK...WITH TRADE WINDS POSSIBLY
RESUMING OVER THE ISLANDS BY SUNDAY OR MONDAY.

&&

.AVIATION...
A MOSTLY DRY PATTERN WILL DEVELOP OVERNIGHT AND TUESDAY AS WEAK
NE-E WINDS BUILD OVER THE ISLANDS IN THE WAKE OF A WEAK FRONT...
THAT IS IN THE PROCESS OF DISSIPATING AS IT MOVES SLOWLY S NEAR
THE BIG ISLAND. THE LIGHT TRADE WINDS WILL DELIVER ISOL MVFR
CIG/VIS IN SHRA TO WINDWARD COASTS AND SLOPES OVERNIGHT AND EARLY
TUESDAY...BUT WEATHER AT THE TERMINALS WILL BE PREVAILING VFR.
LEEWARD CLOUDS WILL INCREASE ONCE AGAIN TUESDAY LATE MORNING AND
AFTERNOON...PRODUCING ISOL MVFR VIS/CIG IN SHRA.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS IN EFFECT FOR SOUTH FACING SHORES
OF ALL ISLANDS THROUGH TUESDAY. SURF REPORTS REACHED HIGH-END
ADVISORY LEVELS AT MANY BEACHES EARLIER TODAY. WAVE HEIGHTS AT THE
BARBERS POINT BUOY ARE RUNNING SLIGHTLY ABOVE WAVEWATCH GUIDANCE
CURRENTLY...AND WOULD EXPECT THAT THE RESULTING SURF WILL REMAIN
ABOVE ADVISORY CRITERIA THROUGH TUESDAY. OBSERVED SWELL PERIODS
ARE SLOWLY DECREASING...AND THE SWELL SHOULD DECREASE ENOUGH TO
ALLOW SURF TO DROP BELOW ADVISORY CRITERIA BY TUESDAY EVENING.
OTHERWISE...A SMALL NORTHWEST SWELL APPEARS TO BE NEAR ITS PEAK
NOW AS INDICATED BY WAIMEA BAY BUOY DATA AND WAVEWATCH GUIDANCE.
THIS SWELL WILL DIMINISH THROUGH TUESDAY...BUT ANOTHER COUPLE OF
SMALL NORTH NORTHWEST SWELLS ARE EXPECTED TO ARRIVE THROUGH
MIDWEEK. RESULTING SURF SHOULD REMAIN WELL BELOW ADVISORY LEVELS
ON NORTH AND WEST FACING SHORES.

WITH EITHER LIGHT TRADES OR A LAND/SEA BREEZE PATTERN FORECAST
TO PREVAIL THROUGH THE REMAINDER OF THIS WEEK AND INTO THE
WEEKEND...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT
ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST TUESDAY FOR SOUTH FACING SHORES
OF ALL ISLANDS.

&&

$$

JACOBSON




Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office