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Hawaiian Islands Synoptic Discussion and Guidance

436
FXHW60 PHFO 301355
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
355 AM HST THU OCT 30 2014

.SYNOPSIS...
A FRONT WILL BRING AN INCREASE IN CLOUDS AND SHOWERS AS IT MOVES
SLOWLY SOUTHWARD ACROSS THE WESTERN AND CENTRAL PARTS OF THE
STATE TODAY AND TONIGHT. LOCALLY HEAVY DOWNPOURS WILL BE POSSIBLE
DURING THIS TIME...AND THERE WILL ALSO BE A SLIGHT CHANCE OF
THUNDERSTORMS OVER KAUAI THIS AFTERNOON. TRADE WINDS WILL INCREASE
TODAY AND TONIGHT AS STRONG HIGH PRESSURE PASSES FAR NORTH OF THE
STATE. A MORE TYPICAL TRADE WIND WEATHER PATTERN SHOULD RETURN
DURING THE WEEKEND AS THE FRONT DISSIPATES AND HIGH PRESSURE MOVES
FURTHER NORTHEAST AND AWAY FROM THE STATE.

&&

.DISCUSSION...
SHOWER ACTIVITY REMAINED FOCUSED ACROSS WINDWARD SECTIONS FROM
KAUAI THROUGH MAUI DURING THE OVERNIGHT HOURS...WITH SHOWERS
DECREASING SOMEWHAT RECENTLY JUST AHEAD OF AN APPROACHING FRONT.
MOST OF THE SHOWERS HAVE BEEN LIGHT TO MODERATE...WHICH COMBINED
WITH QUICK MOVEMENT HAS KEPT RAINFALL AMOUNTS FROM BECOMING TOO
HEAVY IN ANY GIVEN LOCATION. A LONE CUMULONIMBUS HAS DEVELOPED
DURING THE PAST COUPLE OF HOURS ABOUT 80 MILES NORTH OF OAHU...
WITH SATELLITE/RADAR ESTIMATED TOPS UP AROUND 35-40K FEET. SURFACE
ANALYSIS DEPICTS A WEAK FRONT ABOUT 70 MILES NORTH OF KAUAI...WITH
STRONG HIGH PRESSURE CENTERED ABOUT 1150 MILES TO THE NNW. THIS
HIGH IS FORCING THE FRONT TO MOVE SLOWLY SOUTHWARD TOWARD THE
STATE. ALOFT...A LONGWAVE TROUGH IS LOCATED BETWEEN 140W AND
150W....WITH WATER VAPOR IMAGERY INDICATING A SHORTWAVE DROPPING
SOUTHWARD ALONG 160W ALONG THE WEST SIDE OF THE LARGER TROUGH.
MIMIC-TPW IMAGERY INDICATES A STRIPE OF ENHANCED MOISTURE ALONG
THE FRONT...WITH ANOTHER AREA OF HIGHER MOISTURE SHIFTING SOUTH
AND WEST OF THE STATE. THE 12Z SOUNDINGS REFLECTED FAIRLY TYPICAL
CONDITIONS PRESENT AHEAD OF THE FRONT...WITH PWATS NEAR NORMAL AT
JUST OVER 1.3 INCHES AND SOMEWHAT ELEVATED INVERSIONS BASED
BETWEEN 8000 AND 10000 FEET.

TODAY AND TONIGHT...THE FRONT WILL MOVE SLOWLY SOUTHWARD ACROSS THE
SMALLER ISLANDS...AS THE STRONG SURFACE HIGH MOVES EASTWARD WELL
TO OUR NORTH. ALTHOUGH LOW LEVEL CONVERGENCE WILL BE LACKING
ALONG THIS FEATURE WITH INCREASING TRADE WIND FLOW ALREADY IN
PLACE...ENHANCED MOISTURE ALONG WITH INCREASING INSTABILITY DUE TO
A DEVELOPING MID/UPPER LEVEL TROUGH OVERHEAD SHOULD ALLOW FOR SOME
OF THE SHOWERS TO BECOME LOCALLY HEAVY. THE BEST CHANCES FOR HEAVY
DOWNPOURS WOULD APPEAR TO BE ACROSS KAUAI AND OAHU THIS AFTERNOON
AND TONIGHT...POSSIBLY SPREADING INTO MAUI COUNTY AS WELL TONIGHT.
LOCALLY DERIVED MOISTURE-STABILITY INDICES INDICATE THE POTENTIAL
FOR ISOLATED THUNDERSTORMS AS WELL TODAY...MAINLY ACROSS NORTHERN
AND WESTERN SECTIONS. THE RECENT CB DEVELOPMENT NORTH OF THE
COASTAL WATERS ADDS CONFIDENCE TO THIS IDEA...AND HAVE INCLUDED
THUNDER IN THE FORECAST FOR KAUAI THIS AFTERNOON. THUNDER CHANCES
APPEAR TO DECREASE TONIGHT...BUT CANNOT BE TOTALLY RULED OUT FOR
THIS EVENING.

THE FRONT WILL THEN GRADUALLY DISSIPATE ACROSS THE STATE FRIDAY
THROUGH SATURDAY...WITH THE MID/UPPER TROUGH LINGERING NEAR OR
JUST TO THE SOUTHWEST OF THE AREA. FRESH TRADE WINDS WILL CONTINUE
TO DRIVE SHOWERS INTO WINDWARD AREAS...CARRYING OVER INTO SOME
LEEWARD SECTIONS. A FEW HEAVIER DOWNPOURS WILL REMAIN POSSIBLE AS
WELL DUE TO LINGERING INSTABILITY ALOFT...BUT RAPID SHOWER MOTIONS
SHOULD KEEP MOST RAINFALL AMOUNTS FROM BECOMING EXCESSIVE.

TRADES SHOULD DECREASE SOMEWHAT FROM SUNDAY INTO EARLY NEXT WEEK...
AS THE SURFACE HIGH SHIFTS FURTHER TO THE EAST AND ANOTHER COLD
FRONT MOVES SLOWLY SOUTHEAST TOWARD THE STATE. WOULD GENERALLY
EXPECT A TYPICAL TRADE WIND WEATHER PATTERN TO PREVAIL...ALTHOUGH
SOME OF THE MODELS CONTINUE TO ENTRAIN DEEPER TROPICAL MOISTURE
NORTHWESTWARD ACROSS THE STATE AHEAD OF THE NEXT FRONT EARLY NEXT
WEEK...WHICH COULD RESULT IN HIGHER RAIN CHANCES. THIS FRONT MAY
EVENTUALLY REACH THE WESTERN/CENTRAL PARTS OF THE STATE BY NEXT
WEDNESDAY OR THURSDAY...BUT IT IS TOO SOON TO HAVE MUCH CONFIDENCE
IN THIS.

&&

.AVIATION...
EXPECT VFR TO RULE TODAY...EXCEPT FOR KAUAI WHERE CLOUDS AND SHOWERS
FROM A DISSIPATING FRONT MOVES IN EARLY THIS AFTERNOON THAT MAY
WARRANT AIRMET SIERRA FOR WIDESPREAD MTN OBSCURATION. WE EXPECT THE
TRADES TO STRENGTHEN AREA WIDE AS FRONT BREAKS UP. HOWEVER...LO LVL
TURBC IS A QUESTION MARK SINCE THE INVERSION IS EXPECT TO BE WEAK.
SO WE WILL HOLD BACK ON ISSUING AIRMET TANGO FOR LO LVL TURBC AND
CONTINUE TO MONITOR FOR SIGNS OF IT.

THE FRONT IS ABOUT 70 NM NORTH OF KAUAI MOVING SOUTH SLOWLY. AFTER
REACHING KAUAI EARLY THIS AFTERNOON...THE FRONT WILL CONTINUE TO
FALL APART UPON REACHING THE CENTRAL ISLANDS DURING THE FIRST HALF
OF TONIGHT. AIRMET SIERRA IS LIKELY TO EXPANDED TO INCLUDE THESE
ISLANDS.

CURRENTLY...CONDS ARE RELATIVELY DRY STATEWIDE. THE PATCHY LOW
CLOUDS AND EMBEDDED SHOWERS HARASSING MAUI COUNTY UNEXPECTEDLY
DISSIPATED. SCATTERED SHOWERS ARE MOVING THROUGH OAHU NOW BUT THIS
AREA CONTINUES TO SHRINK AND DISSIPATE. LOW CLOUDS WITH EMBEDDED
SHOWERS HAVE INCREASED ACROSS KAUAI BUT IS NOT WIDESPREAD TO WARRANT
AIRMET SIERRA. THE SHOWERS CONTAINS BRIEF MVFR CEILINGS AND
VIS...AND THEY WILL BE FAVORING THE WINDWARD AND MTN AREAS. WINDWARD
BIG ISLAND STILL HAS SOME SHALLOW CLOUDS ALONG ITS SHORELINE AND ADJ
WATERS BETWEEN UPOLU POINT AND HILO...WHILE THE AFTERNOON CLOUDS OF
YESTERDAY...HAVE DEPARTED HT KONA SIDE. WE EXPECT THE CLOUDS TO
RETURN TO THE KONA SIDE THIS AFTERNOON.

THE LEADING EDGE TO A BAND OF DENSE HIGH CLOUDS IS JUST TOUCHING
SOUTHERNMOST BIG ISLAND. IT IS THREATENING TO SPREAD NORTH AS THE
DAY PROGRESSES.

&&

.MARINE...
THE EXPECTED NORTH SWELL HAS CONTINUED TO ARRIVE ACROSS THE
HAWAIIAN COASTAL WATERS OVERNIGHT...AS DEPICTED BY DATA FROM THE
CDIP MOKAPU POINT BUOY. THIS SWELL IS EXPECTED TO PEAK LATER
TODAY...WITH ANOTHER REINFORCING NORTH SWELL ARRIVING TONIGHT
INTO FRIDAY. THESE SWELLS...IN COMBINATION WITH STRONG TRADE
WINDS EXPECTED TO BUILD TODAY AND TONIGHT...WILL BRING HAZARDOUS
SURF CONDITIONS TO EAST FACING SHORES OF THE STATE THROUGH EARLY
SATURDAY MORNING. A HIGH SURF ADVISORY REMAINS IN EFFECT FOR EAST
FACING SHORES. NORTH FACING SHORES WILL ALSO SEE A BOOST TO SURF
OVER THE NEXT FEW DAYS...BUT SURF HEIGHTS WILL REMAIN BELOW
ADVISORY CRITERIA THERE. SURF ALONG THE SOUTH FACING SHORES WILL
REMAIN SMALL THROUGH MONDAY...WITH A SLIGHT BUMP TUESDAY AS A NEW
LONG PERIOD SWELL ARRIVES. ANOTHER SMALL NORTHWEST SWELL WILL
ARRIVE TUESDAY AS WELL.

THE OVERNIGHT ASCAT PASS FOUND SOLID AREAS OF 25 KNOT WINDS ACROSS
THE TYPICALLY WINDY MARINE ZONES SOUTH OF THE BIG ISLAND AND IN
THE ALENUIHAHA CHANNEL. SMALL CRAFT ADVISORY CONDITIONS WILL
SPREAD INTO MOST OTHER MARINE ZONES LATER TODAY AS WINDS AND SEAS
BUILD FURTHER...THEN CONTINUING THROUGH FRIDAY NIGHT AND POSSIBLY
INTO SATURDAY. WINDS AND SWELL WILL BEGIN TO TAPER OFF DURING THE
WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SATURDAY FOR EAST FACING SHORES
OF KAUAI OAHU MOLOKAI MAUI AND BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY FROM 6 AM THIS MORNING TO 6 AM HST SATURDAY
FOR KAUAI NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD
WATERS-KAUAI CHANNEL-OAHU WINDWARD WATERS-KAIWI CHANNEL-MAUI
COUNTY WINDWARD WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...LAU




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