FXHW60 PHFO 220143
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST TUE MAY 21 2013
.SYNOPSIS...
A WEAKENING LOW TO OUR NORTH AND A TROUGH JUST WEST OF KAUAI WILL 
KEEP WINDS LIGHT ACROSS THE STATE...LEADING TO OFFSHORE LAND BREEZES 
AT NIGHT AND ONSHORE SEA BREEZES DURING THE DAY. CLOUDS AND SHOWERS 
FOCUSED ACROSS INTERIOR SECTIONS OF THE ISLANDS EARLY EVENING WILL 
DIMINISH THIS EVENING...THEN ARE POSSIBLE AGAIN WEDNESDAY AFTERNOON. 
AS THE LOW MOVES WEST AND DISSIPATES...TRADE WINDS WILL RETURN 
BEGINNING THURSDAY AND STRENGTHEN THROUGH THE WEEKEND. 
 
&&
.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW OVER 600 MILES NORTH 
NORTHEAST OF THE STATE...WITH AN UPPER TROUGH EXTENDING ABOUT 200 
MILES NORTHWEST OF KAUAI. AT THE SURFACE...LOW PRESSURE IS LOCATED 
LESS THAN 500 MILES NORTH OF KAUAI...WITH A TROUGH MOVING WELL WEST 
OF THE ISLAND. 00Z RAOB SHOW INVERSIONS HAVING STRENGTHENED OVER 
THE PAST 24 HOURS...BUT STILL REMAINING ELEVATED AROUND 8-9KFT. 
PRECIPITABLE WATERS ALSO RANGE FROM 1.1 INCHES AT LIHUE TO 1.5 
INCHES AT HILO. EARLY AFTERNOON MIMIC TOTAL PRECIPITABLE WATER 
IMAGERY SHOWS HIGHER MOISTURE FROM OAHU EASTWARD...PART OF A 
CONVERGENCE BAND THAT EXTENDS FAR NORTHEAST OF THE STATE. 
WITH THE WEAK SURFACE FEATURES NEARBY...THE PRESSURE GRADIENT ACROSS 
THE ISLANDS REMAINS QUITE WEAK. THE PRESSURE DIFFERENCE BETWEEN BUOY 
51101 TO THE NORTHWEST OF KAUAI AND BUOY 51003 TO THE SOUTH OF KAUAI 
HAS RISEN TO AROUND 1MB...WHICH IS STILL SLIGHTLY LESS THAN THE 
VALUES OBSERVED YESTERDAY. WIDESPREAD SEA BREEZES FORMED 
TODAY...AND LAND BREEZES ARE EXPECTED AGAIN TONIGHT. THIS TYPE OF 
CONVECTIVE PATTERN IS EXPECTED TO CONTINUE THROUGH WEDNESDAY...WITH 
AFTERNOON CLOUDS AND SHOWERS AND SOME CLEARING AT NIGHT. A BAND OF 
HIGH CLOUDS HAS FILLED IN OVER THE SMALLER ISLANDS EARLIER IN THE 
DAY AHEAD OF THE UPPER TROUGH...BUT ARE BEGINNING TO PULL AWAY TO 
THE EAST NORTHEAST. DESPITE OFFSHORE LAND BREEZES TONIGHT...WE MAY 
NOT SEE THE DEGREE OF CLEARING AS IN PAST NIGHTS AS MOISTURE AND 
CLOUDS FROM THE CONVERGENCE BAND EAST AND NORTHEAST OF THE STATE 
SPREAD WESTWARD. 
THE LOW NORTH OF THE STATE IS EXPECTED TO MOVE WESTWARD AND 
DISSIPATE...WITH THE SURFACE TROUGH MOVING FARTHER WEST OF KAUAI. 
THE GRADIENT REMAINS LIGHT THROUGH WEDNESDAY...WHICH WILL ALLOW FOR 
ANOTHER DAY OF ONSHORE SEA BREEZES AND AFTERNOON CLOUDS AND SHOWERS. 
THE ATMOSPHERE STABILIZED TODAY...WHICH LIMITED RAINFALL AMOUNTS 
ACROSS THE SMALLER ISLANDS...AND WILL STABILIZE FURTHER ON 
WEDNESDAY. HOWEVER...THE MOISTURE SPREADING WESTWARD MAY HELP TO 
ENHANCE SHOWERS DURING THE AFTERNOON. 
HIGH PRESSURE NORTHEAST OF THE STATE WILL REASSERT ITSELF ACROSS THE 
ISLANDS BY THURSDAY. AS THIS HIGH MOVES SOUTHWARD AND THE RIDGE 
REESTABLISHES ITSELF NORTH OF THE STATE...WE SHOULD SEE 
STRENGTHENING TRADE WINDS THROUGH THE WEEKEND. HOWEVER...AN UPPER 
LEVEL LOW DEVELOPING TO OUR NORTHEAST WILL HELP TO DESTABILIZE THE 
AIRMASS BY THE WEEKEND. WHILE THE LATEST MODEL RUNS SHOW THIS 
FEATURE CONFINED TO UPPER LEVELS...WITH TRADES PERSISTING AT THE 
SURFACE...IT WILL HELP TO ERODE THE TRADE WIND INVERSION AND ENHANCE 
TRADE WIND SHOWERS. THIS PATTERN IS EXPECTED TO LINGER INTO EARLY 
NEXT WEEK. 
&&
.AVIATION...
VFR CONDITIONS PREVAIL AT MOST OF THE TAF SITES WITH SOME LOCAL MVFR 
IN THE VICINITY OF PHTO DUE TO VOLCANIC EMISSIONS. THESE CONDITIONS 
WILL LIKELY PERSIST THROUGH THE NIGHT. DAYTIME HEATING HAS CAUSED 
SOME MVFR CONDITIONS TO OCCUR MAINLY OVER THE BIG ISLAND DUE TO 
CLOUDS AND SHRA. CONDITIONS WILL LIKELY IMPROVE OVERNIGHT.
&&
.MARINE...
THE CURRENT SOUTH SWELL REMAINS ELEVATED...AND WAVEWATCH GUIDANCE 
SHOWS ADDITIONAL ENERGY AFFECTING THE AREA TONIGHT/WEDNESDAY. BASED 
ON CURRENT OBSERVATIONS AND A GRADUAL DOWNWARD TREND...WE WILL 
EXTEND THE HIGH SURF ADVISORY THROUGH WEDNESDAY. BEYOND 
WEDNESDAY...SURF WILL CONTINUE TO GRADUALLY DIMINISH THROUGH THE 
WEEK. A NEW LONGER-PERIOD WEST-NORTHWEST SWELL WILL CONTINUE TO 
BUILD TONIGHT AND PEAK WEDNESDAY INTO THURSDAY. WHILE THIS SWELL IS 
LARGER THAN NORMAL FOR THIS TIME OF YEAR...SURF IS EXPECTED TO 
REMAIN BELOW ADVISORY LEVELS FOR NORTH AND WEST FACING SHORES. 
TRADE WINDS ARE EXPECTED TO BE STRONG ENOUGH BY THE WEEKEND FOR 
SMALL CRAFT WIND CONDITIONS TO DEVELOP OVER THE WINDIER AREAS AROUND 
MAUI COUNTY AND THE BIG ISLAND. 
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST WEDNESDAY FOR SOUTH FACING SHORES 
OF ALL ISLANDS.
WIND ADVISORY UNTIL 6 AM HST WEDNESDAY FOR BIG ISLAND SUMMITS.
&&
$$
PUBLIC/MARINE...BRAVENDER
AVIATION...BURKE