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Hawaiian Islands Synoptic Discussion and Guidance

049
FXHW60 PHFO 180304 CCA
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
408 PM HST WED SEP 17 2014

.SYNOPSIS...
HIGH PRESSURE NORTH OF THE STATE IS EXPECTED TO WEAKEN TONIGHT
ALLOWING WINDS TO WEAKEN. EXPECT LAND AND SEA BREEZES TO SET UP
THURSDAY THROUGH THE WEEKEND RESULTING IN WARM TEMPERATURE...
AFTERNOON CLOUDS. ISOLATED SHOWERS WILL BE POSSIBLE WITH THE
AFTERNOON CLOUDS BUT STABILITY WILL KEEP ANY SHOWERS LIGHT. A
TROPICAL WAVE PASSING SOUTH OF THE AREA MAY BRING AN INCREASE IN
RAINFALL ACROSS THE BIG ISLAND WITH GENTLE TRADE WINDS RESUMING
ACROSS THE STATE MONDAY.

&&

.DISCUSSION...
VISIBLE SATELLITE IMAGERY SHOWS LOW CLOUD BUILD UPS OVER THE
LEEWARD AND INTERIOR SECTIONS OF THE ISLANDS THIS AFTERNOON...WHILE
MOSTLY SUNNY TO PARTLY CLOUDY SKIES PREVAIL OVER MOST WINDWARD
SIDES. SCATTERED CLOUD ALSO PERSIST UPSTREAM OF THE SMALLER ISLANDS
WHICH ARE GENERALLY MOVING NORTHEAST TO SOUTHWEST AT 5 TO 10 MPH.
RADAR
IS PICKING UP ISOLATED SHOWERS WITHIN ALL OF THE CLOUD COVER.
GENTLE TRADE WINDS OVER HAWAII ARE DRIVEN BY A 1021 MB SURFACE
HIGH LOCATED FAR TO THE NORTH-NORTHWEST.

ALOFT...A WEAK UPPER LEVEL LOW IS CENTERED NEAR KAUAI...WITH A LARGE
MID/UPPER LEVEL RIDGE LOCATED TO THE NORTH OF THE STATE. MIMIC-
TOTAL PRECIPITABLE WATER /PW/ SATELLITE IMAGERY SHOWS A STRIPE OF
HIGHER MOISTURE ASSOCIATED WITH THE CLOUDS JUST NORTH OF THE
SMALLER ISLANDS. THIS AREA OF MOISTURE IS MOVING TO THE WEST-
SOUTHWEST TOWARDS KAUAI AND OAHU. THE 00Z SOUNDINGS DEPICT A
RATHER TYPICAL PROFILE...WITH INVERSIONS BASED AROUND 8000
FEET...AND NEAR NORMAL PW VALUES BETWEEN 1.3 AND 1.5 INCHES.

FOR TONIGHT...EXPECT THE CLOUDS AND SHOWERS TO DECREASE AS LAND
BREEZES OVER POWER THE WEAK TRADE WIND FLOW. A COLD FRONT IS
EXPECTED TO MOVE SOUTHEASTWARD ACROSS THE NORTH CENTRAL PACIFIC
OVER THE NEXT FEW DAYS. THE FRONT WILL WEAKEN THE HIGH NORTH OF
US...AND RESULT IN A PURE SEA AND LAND BREEZE PATTERN. THIS
PATTERN WILL BRING MOSTLY CLEAR NIGHTS AND MORNINGS. AFTERNOONS
AND EVENINGS WILL SEE CLOUD BUILD UPS AND SPOTTY SHOWERS OVER
INTERIOR AREAS. THE LIGHT WINDS WILL ALLOW VOLCANIC HAZE TO BUILD
UP AROUND THE BIG ISLAND...BUT IT DOES NOT APPEAR AS IF THERE WILL
BE ENOUGH SOUTHERLY COMPONENT IN THE FLOW TO CARRY THE HAZE OVER
THE SMALLER ISLANDS.

GFS AND ECMWF COMING INTO LINE FOR A TROPICAL WAVE PASSING SOUTH
OF THE STATE SUNDAY...WITH BOTH MODELS SUGGESTING THAT NORTHERN
FRINGES OF THE PLUME OF MOISTURE WILL BARELY BRUSH ACROSS THE BIG
ISLAND. THIS MAY BRING AN INCREASE IN SHOWERS AT THIS TIME.

IT ALSO APPEARS THE EARLIER MENTIONED COLD FRONT WILL STALL OUT
AND DISSIPATE ABOUT 300 MILES NORTH OF THE STATE. THE INCREASED
PRESSURE GRADIENT BETWEEN LOWER PRESSURE TO THE SOUTH...AND A
NARROW HIGH PRESSURE RIDGE BETWEEN THE ISLANDS AND A STALLED
FRONTAL BOUNDARY TO OUR NORTH SHOULD INDUCE SOME INCREASE IN
EASTERLY FLOW OVER THE STATE DURING BY MONDAY. HIGH PRESSURE WILL
SLOWLY STRENGTHEN BEHIND THIS WEAKENING FRONT EVENTUALLY PUSHING
OVER THE HAWAIIAN ISLANDS BY MIDWEEK. LOOK FOR A SLOW UPTICK IN
THE TRADE WINDS TUESDAY AND WEDNESDAY OF NEXT WEEK. AT THAT
TIME...SHOWERS WILL BEGIN TO FOCUS BACK ONTO WINDWARD SIDES OF THE
ISLANDS.


&&

.AVIATION...
OVERNIGHT...ISOL MVFR SHOWERS AND CLOUDS WILL MAINLY AFFECT
WINDWARD AREAS. THE LOCALIZED CLOUD BUILDUPS AND SHOWERS OVER
LEEWARD AREAS WILL BEGIN TO CLEAR WITH SUNSET. VFR CONDITIONS WILL
PREVAIL AT ALL ISLAND TERMINALS.


&&

.MARINE...
BUOY READINGS AT BARBERS POINT HAVE SHOWN A SMALL DROP OFF IN SWELL
HEIGHTS THROUGH THE DAY. THIS SWELL WILL SLOWLY FADE AWAY THROUGH
FRIDAY. A SMALL LONG PERIOD SOUTH SWELL WILL BUILD IN THIS
EVENING...WHICH WILL HELP KEEP SMALL SURF ALONG SOUTH FACING
SHORES THROUGH THE WEEKEND. SURF ALONG NORTH FACING SHORES WILL
ALSO DECREASE TONIGHT.

ELSEWHERE...A SMALL NORTHWEST SWELL ARRIVED LATE YESTERDAY...AS
INDICATED BY WAIMEA BAY BUOY DATA. ANOTHER SMALL NORTHWEST SWELL
WILL ARRIVE LATER TODAY...BUT SURF ALONG NORTH FACING SHORES WILL
REMAIN WELL BELOW ADVISORY LEVELS. NO OTHER MAJOR SWELLS ARE IN
THE FORECAST.

WINDS WILL REMAIN LIGHT THROUGH MOST OF THE FORECAST PERIOD AND NO
SMALL CRAFT ADVISORY IS EXPECTED. THE TRADE WINDS SHOULD BEGIN TO
STRENGTHEN MONDAY.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...EATON






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