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Hawaiian Islands Synoptic Discussion and Guidance

791
FXHW60 PHFO 282001
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1001 AM HST WED JAN 28 2015

.SYNOPSIS...
A WEAK FRONT WILL BRING A SLIGHT BOOST TO SHOWERS AS IT PASSES OVER
THE STATE THURSDAY NIGHT INTO FRIDAY. WEAK TRADE WINDS WILL
PRODUCE PRIMARILY WINDWARD AND MAUKA SHOWERS TO MAUI AND THE BIG
ISLAND THIS WEEKEND. A STRONGER FRONT WILL PASS OVER THE STATE
MONDAY NIGHT INTO TUESDAY NIGHT FOLLOWED BY ANOTHER FRONTAL PASSAGE
WEDNESDAY NIGHT INTO THURSDAY.

&&

.DISCUSSION...
A SLOW MOVING COLD FRONT IS LOCATED ABOUT 400 MILES NORTHWEST OF
KAUAI. MEANWHILE...A COMPLEX LOW PRESSURE SYSTEM TO OUR NORTH HAS
MOVED THE SUBTROPICAL HIGH FURTHER AWAY TO THE NORTHEAST...AND THE
ASSOCIATED RIDGE AXIS CROSSES THE EASTERN END OF THE STATE. THE
RESULT IS WEAK SOUTHEAST FLOW OVER THE ISLANDS.

THE ATMOSPHERE REMAINS RATHER STABLE THIS MORNING AS STRONG
MIDLEVEL RIDGING REMAINS PARKED OVER THE STATE. 12Z SOUNDINGS FROM
EARLY THIS MORNING SHOW INVERSIONS AT AROUND 6000 FEET.
PRECIPITABLE WATER VALUES WERE AROUND 1 INCH. VISIBLE SATELLITE
SHOWS QUITE A BIT OF STRATOCUMULUS OVER MOST COASTAL WATERS THIS
MORNING. THE THICKEST CLOUD AREA IS ACROSS THE EAST AND SOUTHEAST
BIG ISLAND WATERS. THE SOUTHEAST FLOW IS WRAPPING SOME OF THIS
CLOUD COVER SOUTH OF THE BIG ISLAND AND THEN TO THE NORTH AROUND
THE SMALLER ISLANDS THIS MORNING.

THE FORECAST CHALLENGE FOR TODAY WILL BE CLOUD COVER...AND WILL
DEPEND ON HOW MUCH MIXING AND CLOUD-TOP WARMING OCCURS THIS
MORNING OVER THE ISLANDS. SOME ISLANDS STARTED THE DAY MOSTLY
SUNNY WHILE OTHERS WERE UNDER THE LOW CLOUDS. EXPECTING TO SEE
ENOUGH CLEARING THIS MORNING TO ALLOW SEA BREEZES TO KICK IN BY
AFTERNOON. THE SEA BREEZES WILL THEN PRODUCE CLOUD BUILD UPS OVER
THE ISLANDS. THE STABLE AIR WILL LIKELY RESULT IN A FEW LIGHT
SHOWERS THIS AFTERNOON OVER LEEWARD AND INTERIOR AREAS.

THE LIGHT WINDS WILL CONTINUE UNTIL THURSDAY NIGHT ALLOWING THIS
PATTERN OF DAYTIME SEA BREEZES AND NIGHTTIME LAND BREEZES TO
CONTINUE. THE AFOREMENTIONED COLD FRONT TO THE NORTHWEST IS EXPECTED TO
MOVE SOUTHEAST OVER THE STATE THURSDAY NIGHT AND FRIDAY. GFS AND
ECMWF MODELS DEPICT A WEAK FRONT THAT WILL LIKELY PRODUCE A SMALL
UPTICK IN SHOWERS AS IT PASSES. WINDS ARE EXPECTED TO SWING AROUND
TO THE NORTHWEST AND STRENGTHEN SLIGHTLY ON FRIDAY...THEN SHIFT TO
THE NORTHEAST BY FRIDAY NIGHT AS WEAK RIDGING SETS UP JUST NORTH
OF THE STATE.

THE FRONT WILL STALL OUT EAST OF THE BIG ISLAND...BUT NORTHEAST
TRADE WINDS COULD FUNNEL SOME OF THE MOISTURE BACK OVER WINDWARD
MAUI AND BIG ISLAND THIS COMING WEEKEND FROM THE THURSDAY NIGHT /
FRIDAY FRONTAL PASSAGE. THESE WINDWARD SHOWERS SHOULD BE ON THE
LIGHTER SIDE. LEEWARD AREAS SHOULD REMAIN PLEASANT THIS WEEKEND.

WINDS WILL WEAKEN AND SHIFT SOUTH TO SOUTHEAST AGAIN BEGINNING
SUNDAY NIGHT AS A DEVELOPING SURFACE LOW AND ASSOCIATED FRONT TO
THE NORTHWEST MOVES CLOSER TO THE STATE. LONG-RANGE MODELS
PASS THE LOW NORTH OF US WHILE THE FRONT WILL MOVE THROUGH MONDAY
NIGHT TO TUESDAY NIGHT. WINDS WILL STRENGTHEN OUT OF THE
SOUTHWEST AHEAD OF THE FRONT ON MONDAY...THEN SHIFT WEST BEHIND
IT. THIS FRONT WILL BE A BIT MORE ROBUST AND CAPABLE OF PRODUCING
BLUSTERY CONDITIONS WITH FRESH TO STRONG WINDS AND SHOWERS. MOST
OF THE UPPER LEVEL DYNAMICS AND INSTABILITY WILL STAY NORTH OF THE
STATE...SO AT THIS TIME WE ARE NOT ANTICIPATING THUNDERSTORMS.

MODELS DEPICT A SECOND ROBUST FRONT WITH SIMILAR CHARACTERISTICS PASSING
OVER THE ISLANDS WEDNESDAY NIGHT AND THURSDAY.


&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL ACROSS THE STATE TODAY. GOOD AMOUNT OF
STABLE STRATOCUMULUS CLOUDS AROUND THE ISLANDS BUT WITH FAIRLY HIGH
BASES. AND MUCH OF THIS CLOUDINESS IS EXPECTED TO BURN OFF DURING
THE DAY FROM THE SUN AND WITH ADDITIONAL...THOUGH PERHAPS
TEMPORARY...HELP OF GRAVITY WAVES OCCASIONALLY PASSING THROUGH THE
AREA FROM THE NORTHWEST.

LIGHT WINDS...THOUGH MAINLY SOUTHEAST TO SOUTHERLY...WILL PERSIST
AROUND THE STATE THROUGH THURSDAY. A RELATIVELY WEAK FRONT EXPECTED
TO REACH KAUAI THURSDAY MORNING...MAY STALL AND DISSIPATE BEFORE
REACHING OAHU. THIS...AND THE FACT THAT A LARGE LOW PRESSURE AREA
WILL SIT N OF THE STATE GOING INTO THE WEEKEND WILL KEEP TRADE
WINDS AWAY FROM THE AREA FOR AWHILE. EPISODES OF LAND BREEZES BY
NIGHT AND SEA BREEZES DURING THE DAY WILL CONTINUE TO FELT AROUND
PARTS OF THE ISLANDS...INCLUDING MOST OF THE AIRPORTS.


&&

.MARINE...
THE CURRENT NORTHWEST SWELL PRODUCING ADVISORY LEVEL SURF FOR
MOST NORTH AND WEST FACING SHORES WILL DIMINISH THURSDAY NIGHT.
REINFORCING SWELL FROM THE NORTHWEST WILL ARRIVE FRIDAY AND
SATURDAY. FRIDAY/S SWELL WILL PRODUCE SURF NEAR ADVISORY LEVELS
FOR NORTH AND WEST SHORES...WITH SATURDAY/S SWELL LIKELY MOVING
SURF INTO ADVISORY CRITERIA. THE SATURDAY SWELL WILL BE FROM THE
320-330 DIRECTION WHICH WILL MAKE MOST OF THE IMPACT ACROSS NORTH
FACING SHORES. THIS SWELL WILL GRADUALLY DIMINISH THROUGH TUESDAY.
COMBINED SEAS AND WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT
ADVISORY OVER THE NEXT SEVERAL DAYS.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST THURSDAY FOR NORTH AND WEST
FACING SHORES OF NIIHAU KAUAI AND OAHU...AND FOR NORTH FACING
SHORES OF MOLOKAI AND MAUI.


&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...FUJII


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