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000
FXHW60 PHFO 070141
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST THU MAR 6 2014

.SYNOPSIS...
A SURFACE RIDGE OVER THE STATE WILL MOVE EAST AS A FRONT APPROACHES
FROM THE NORTHWEST. THE FRONT IS EXPECTED TO REACH KAUAI ON FRIDAY
AND STALL AND DISSIPATE OVER THE EASTERN HALF OF THE STATE THIS
WEEKEND. SHOWERS WILL INCREASE AHEAD OF THE FRONT OVER THE SMALLER
ISLANDS TONIGHT AND FRIDAY...AND SPREAD FARTHER EAST FRIDAY NIGHT.
TRADE WINDS WILL RETURN BEHIND THE FRONT AS HIGH PRESSURE BUILDS
NORTH OF THE STATE.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A LARGE UPPER LEVEL LOW FAR NORTH OF THE
STATE...WITH A STRONG JET ALONG/NORTH OF 30N. A SHORTWAVE TROUGH IS
LOCATED NEAR THE DATELINE...EMBEDDED WITHIN THE FAST NEARLY ZONAL
FLOW. AT THE SURFACE...A LARGE AND COMPLEX LOW IS LOCATED FAR NORTH
OF THE STATE...WITH A COLD FRONT ABOUT 400 MILES NORTHWEST OF KAUAI.
THE 00Z SOUNDING FROM LIHUE SHOWS A SLIGHTLY WEAKER INVERSION
COMPARED TO 12Z...AS WELL AS AN INCREASE IN MID-LEVEL MOISTURE. THE
HILO SOUNDING ALSO SHOWS A WEAK AND ELEVATED INVERSION. PRECIPITABLE
WATERS ARE 1.3-1.4 INCHES...WHICH SUPPORTS THE EARLY AFTERNOON MIMIC
TOTAL PRECIPITABLE WATER IMAGERY. THE INCREASE IN PW AT LIHUE /FROM
0.91 AT 12Z TO 1.32 AT 00Z/ IS FROM MOISTURE ADVECTION FROM THE
SOUTHWEST OF THE STATE. THERE IS A NARROW BAND OF DRIER AIR JUST
NORTHWEST OF KAUAI...WITH HIGHER VALUES FARTHER NORTHWEST NEAR THE
FRONT.

THE SURFACE RIDGE NEAR THE ISLANDS WILL KEEP WINDS GENERALLY ON THE
LIGHT SIDE...ESPECIALLY ACROSS MAUI COUNTY AND THE BIG ISLAND. WINDS
WILL BE GENERALLY SOUTHEASTERLY...AND LIGHT ENOUGH TO ALLOW
LOCALIZED LAND BREEZES TO FORM. THE WESTERN ISLANDS WILL SEE A
BETTER DEFINED SOUTHWESTERLY GRADIENT. MODERATE TO LOCALLY HEAVY
SHOWERS ARE PASSING ACROSS THE SMALLER ISLANDS...HAVING FORMED ALONG
THE NOSE OF THE MOISTURE AXIS. THERE MAY BE A BRIEF BREAK IN
ACTIVITY LATE THIS AFTERNOON BEHIND THE INITIAL MOISTURE ADVECTION.
HOWEVER...SHOWERS ASSOCIATED WITH PREFRONTAL CONVERGENCE WILL LIKELY
FILL IN DURING THE EVENING. THEREFORE WE KEPT THE MENTION OF HIGH
POPS AND LOCALIZED HEAVY RAIN THROUGH THE NIGHT.

THE GFS AND ECMWF SHOW THE MAIN SURGE OF MOISTURE OCCURRING LATE
TONIGHT INTO FRIDAY...WITH CROSS SECTIONS SHOWING THE DRY LAYER
QUICKLY ERODING. FORECAST SOUNDINGS SHOW LOW- TO MID-LEVEL WINDS
GENERALLY OUT OF THE WEST OR WEST-SOUTHWEST. THIS MAY ACCOUNT FOR
THE SHARPER THETA-E RIDGE BUILDING ACROSS MAUI AND THE BIG ISLAND
BEFORE KAUAI/OAHU. HOWEVER...BASED ON LATE DAY SATELLITE IMAGERY...
THE CONVERGENCE BAND WILL LIKELY FILL IN ACROSS THE WESTERN PART OF
THE STATE. WITH ONLY WEAK UPPER LEVEL FORCING AND RELATIVELY WARM
MID-LEVEL TEMPERATURES...THE SETUP DOES NOT LOOK CONDUCIVE TO
WIDESPREAD FLOODING. BASED ON WEAK INSTABILITY AND INCREASING
MOISTURE...WE WILL MAINTAIN THE MENTION OF LOCALLY HEAVY RAIN...BUT
DO NOT ANTICIPATE CONDITIONS TO WARRANT A FLASH FLOOD WATCH.

12Z MODELS ARE RELATIVELY SIMILAR SHOWING THE FRONT REACHING KAUAI
ON SATURDAY...THEN WEAKENING AND EVENTUALLY STALLING/DISSIPATING
SOMEWHERE IN THE VICINITY OF THE BIG ISLAND BY SUNDAY. HIGH PRESSURE
PASSING NORTH OF THE STATE WILL HELP USHER IN MORE TYPICAL TRADE
WINDS...ALTHOUGH THE TRADE SHOWERS WILL BE HEAVIER THAN NORMAL...AT
LEAST ACROSS THE EASTERN ISLANDS. MID-LEVEL FLOW REMAINS WEAKLY
CYCLONIC...AND FORECAST SOUNDINGS SHOW ONLY A WEAK INVERSION.

HEADING INTO NEXT WEEK...A NEW FRONT WILL PASS NORTH OF THE STATE
MONDAY/TUESDAY...BUT THE 12Z MODELS ARE QUITE SIMILAR IN SHOWING
THAT IT STALLS WELL NORTH OF THE STATE. SOME UPPER-LEVEL ENERGY
ASSOCIATED WITH THIS FEATURE MAY CARVE OUT A TROUGH EAST OF THE
STATE. THIS MAY KEEP MID-LEVEL HEIGHTS LOWER ACROSS THE BIG
ISLAND...EVEN AS A NEW HIGH BUILDS TO THE WEST OF THE STATE.
BUILDING HEIGHTS WILL HELP TO STABILIZE THE ATMOSPHERE...AND HIGH
PRESSURE AT THE SURFACE TO THE NORTHEAST OF THE STATE WILL BRING
TRADE WINDS THROUGH MUCH OF THE WORK WEEK.

&&

.MARINE...
COMBINED SEAS ACROSS THE STATE CONTINUE TO DIMINISH...AND BUOY 51101
ALSO SHOW SEAS RELATIVELY STEADY. BASED ON THE 18Z WAVEWATCH III...A
NEW LARGE NORTHWEST SWELL SHOULD REACH BUOY 51101 LATE TONIGHT. THIS
SWELL WILL BUILD ACROSS THE ISLANDS THROUGH THE DAY ON FRIDAY...AND
PEAK ABOVE WARNING LEVELS FRIDAY NIGHT/SATURDAY. THERE WILL BE AN
INITIAL BUILDUP WITH ADVISORY LEVEL CONDITIONS EXPECTED ON FRIDAY.
BASED ON THE DIFFERENT TIMING ACROSS THE STATE...WE HAVE ISSUED A
HIGH SURF WARNING BEGINNING LATE FRIDAY MORNING. THE BIG ISLAND WILL
ALSO LIKELY SEE ADVISORY LEVEL SURF ALONG WEST FACING SHORES...BUT
WITH A LATER ONSET /DURING THE DAY ON SATURDAY/.

AS THE NEW NORTHWEST SWELL BUILDS ON FRIDAY...A SMALL CRAFT ADVISORY
WILL BE NEEDED FOR EXPOSED COASTAL WATERS DUE TO COMBINED SEAS ABOVE
THE 10 FOOT ADVISORY THRESHOLD. THESE CONDITIONS WILL LIKELY
CONTINUE INTO SUNDAY BEFORE SUBSIDING BELOW 10 FEET.

&&

.AVIATION...
FOR THE BIG ISLAND...WEAK SURFACE HIGH PRESSURE WILL HOLD THROUGH
FRIDAY. GENTLE SEA BREEZES THIS AFTERNOON WILL YIELD TO WEAK LAND
BREEZES THIS EVENING THEN REDEVELOP ON FRIDAY. EXPECT A FEW VFR
SHOWERS OVER MOUNTAIN SLOPES IN THE AFTERNOON AND EVENING HOURS.

ELSEWHERE...WEAK SOUTHWEST FLOW WILL CONTINUE TO ADVECT SCATTERED
MOSTLY VFR SHOWERS ACROSS THE REMAINDER OF THE ISLANDS THROUGH
TONIGHT AND INTO FRIDAY. ISOLATED EMBEDDED HEAVY SHOWERS WILL
PRODUCE BRIEF PERIODS OF MVFR CEILINGS OR VISIBILITIES.

ALSO MAUI WESTWARD...BRISK WEST WINDS AT SUMMIT LEVEL IN COMBINATION
WITH A RELATIVELY STABLE AIRMASS ARE GENERATING TEMPO MODERATE TURB
E AND NE OF MOUNTAIN RANGES. CONDS LIKELY TO CONTINUE THROUGH MOST
OF FRIDAY.

ADDITIONALLY...A DISTANT COLD FRONT TO THE NORTHWEST OF THE ISLANDS
WILL BE APPROACHING KAUAI FRIDAY AFTERNOON. FRONT WILL BE WEAKENING
AS IT APPROACHES THE ISLANDS BUT WIDESPREAD MVFR CIGS AND VIS ARE
NEVERTHELESS POSSIBLE WITH THIS FEATURE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING FROM 10 AM FRIDAY TO 6 AM HST SUNDAY FOR NIIHAU-
KAUAI WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-WINDWARD HALEAKALA.

&&

$$

PUBLIC/MARINE...BRAVENDER
AVIATION...BEDAL