High Surf in Hawaii, July 26 to 27, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST SUN JUL 26 2009

.SYNOPSIS...
HIGH PRESSURE NORTH OF THE STATE WILL MAINTAIN TRADE WINDS THROUGH
THE WEEK. THE HIGH WILL BE STRONG ENOUGH TO KEEP THE TRADES LOCALLY
BREEZY EARLY IN THE WEEK. WITH THE TRADE WINDS...SHOWERS WILL BE
FOCUSED ACROSS WINDWARD AND MAUKA AREAS. IN ADDITION...A TROUGH
ALOFT WILL PRODUCE SOME HIGH CLOUDS ACROSS THE STATE THROUGH MONDAY.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LOW ABOUT 450 MILES NORTH OF
KAUAI...WITH A BROAD RIDGE OVER THE EASTERN HALF OF THE STATE. MID
AND HIGH LEVEL DEBRIS CLOUDS FROM CONVECTION FAR TO THE SOUTH AND
WEST ARE MOVING ACROSS THE STATE IN A GENERAL WEST SOUTHWESTERLY
FLOW BETWEEN THESE TWO FEATURES. 00Z SOUNDINGS FROM LIHUE AND HILO
SHOW PRETTY SOLID INVERSIONS NEAR 4KFT AND 5KFT RESPECTIVELY.
PRECIPITABLE WATERS ARE 1.3-1.6 INCHES...BUT THOSE VALUES ARE
INFLUENCED BY THE AMOUNT OF MID/HIGH LEVEL MOISTURE. LOW LEVELS ARE
RATHER DRY...AS EVIDENCED BY THE LIMITED SHOWER ACTIVITY OVERNIGHT
AND DURING THE DAY.

HIGH CLOUDS WILL CONTINUE TO SPREAD ACROSS THE STATE TONIGHT.
VISIBLE IMAGERY SHOWS MOST OF THE CLOUDS ARE THIN...BUT WITH PATCHES
OF THICKER OPAQUE CLOUDS HEADING TOWARD THE STATE. WILL CARRY A
MINIMUM OF PARTLY CLOUDY SKIES FOR TONIGHT...OF COURSE WITH GREATER
SKY COVER ACROSS WINDWARD AND MAUKA SECTIONS BECAUSE OF THE LOW
LEVEL CLOUDS. GFS FORECAST SOUNDINGS AND CROSS SECTIONS SHOW SOLID
HIGH LEVEL MOISTURE LINGERING ACROSS THE STATE THROUGH MONDAY BEFORE
BEGINNING TO DIMINISH.

THE SURFACE HIGH FAR NORTHEAST OF THE STATE WILL STRENGTHEN THROUGH
MONDAY NIGHT...HELPING TO TIGHTEN THE PRESSURE GRADIENT ACROSS THE
ISLANDS. SURFACE OBSERVATIONS ACROSS THE STATE CONTINUE TO REPORT
PRESSURE RISES OF AROUND 2MB OVER THE PAST 24 HOURS. THE 12Z GFS AND
ECMWF SHOW WINDS SLOWLY INCREASING FOR THE FIRST PART OF THE WEEK...
WITH THE STRONGEST WINDS IN THE ECMWF OCCURRING TONIGHT/MONDAY.
THERE REMAINS GOOD CONSENSUS BETWEEN THE EXTENDED MODELS THAT ONCE
THE TRADE WINDS INCREASE...THEY WILL REMAIN WITH US THROUGH THE END
OF THE FORECAST PERIOD. THE GFS SHOWS THE SUBTROPICAL HIGH WEAKENING
MORE THAN THE ECMWF BY MID WEEK. HOWEVER...BOTH MODELS SHOW THE HIGH
MOVING SOUTHWARD AND MAINTAINING THE PRESSURE GRADIENT ACROSS THE
STATE.

AT UPPER LEVELS...BOTH THE GFS AND ECMWF SHOW THE UPPER LOW NORTH OF
KAUAI MOVING SOUTHEASTWARD AND STALLING JUST EAST OF THE STATE BY
EARLY NEXT WEEK. THE CURRENT GFS HAS TRENDED A BIT FARTHER EAST...
CLOSER TO THE ECMWF SOLUTION. THIS LOW WILL REMAIN NEARLY STATIONARY
THROUGH MID-WEEK BEFORE SLOWLY EDGING NORTHEASTWARD. COOLER
MID-LEVEL TEMPERATURES ASSOCIATED WITH THIS LOW WILL HELP TO
DESTABILIZE THE AIRMASS ACROSS THE STATE ONCE AGAIN. ISOLATED
MODERATE TO HEAVY RAINS MAY AGAIN BE POSSIBLE AS INVERSION HEIGHTS
WEAKEN AND RAISE. HOWEVER...LOW-LEVEL MOISTURE REMAINS SOMEWHAT
LIMITED...AND THE COPIOUS AMOUNTS OF MOISTURE THAT WE SAW THIS PAST
WEEK WILL NOT BE PRESENT.

&&

.MARINE...
BOTH THE LANAI AND KILO NALU BUOYS CONTINUE TO SHOW A 3 FEET/15
SECOND SOUTH SWELL THIS AFTERNOON...WHICH IS STILL A TOUCH HIGHER
THAN THE 18Z WAVEWATCH III GUIDANCE INDICATES. WW3 SHOWS THIS SWELL
MAINTAINING ITS CURRENT HEIGHT THOUGH TONIGHT...BUT WITH A SLOWLY
DECLINING PERIOD...BEFORE RECEIVING A SLIGHT BUMP TO THE HEIGHT ON
MONDAY. THE CURRENT HIGH SURF ADVISORY FOR SOUTH FACING SHORES RUNS
THROUGH MONDAY...AND LOOKS ON TRACK.

THE MORNING QUIKSCAT PASS MISSED US COMPLETELY...BUT THE PASS FROM
LAST EVENING DID SHOW A COUPLE 25 KNOT WIND BARBS IN THE ALENUIHAHA
CHANNEL. SURFACE PRESSURES HAVE CONTINUED TO RISE THROUGH THE DAY
TODAY...AND WINDS AT EXPOSED LAND STATIONS SUCH AS SOUTH POINT AND
KAHOOLAWE HAVE BEEN AROUND 20 KNOTS GUSTING TO 25-30 KNOTS. 12Z
GUIDANCE SHOWS WINDS PEAKING TONIGHT/MONDAY...BUT CONTINUING NEAR
THESE LEVELS LEVELS THROUGH MUCH OF THE WEEK. THE SMALL CRAFT
ADVISORY CONTINUES THROUGH MONDAY...AND WILL LIKELY NEED TO BE
EXTENDED IN TIME.

&&

.AVIATION...
00Z RAOBS AND 23Z-00Z ACARS ASCENT SOUNDING OUT OF PHLI/PHNL THIS
AFTERNOON SHOW WINDS UP TO 20 KNOTS IN THE BOUNDARY LAYER. PHOG IS
THE EXCEPTION OF COURSE...WHERE A COUPLE OF FLIGHTS REPORTED WINDS
UP TO 30 KNOTS IN THE BOUNDARY LAYER. RADAR VAD WIND PROFILES FROM
KAUAI AND MOLOKAI CONTINUE TO SHOW A FEW 25 KNOT WIND REPORTS. IN
ADDITION...VISIBLE SATELLITE IMAGERY THROUGH THE DAY HAS SHOWN WELL
DEFINED WAVE CLOUDS EXTENDING DOWNSTREAM OF THE KOOLAU RANGE ON
OAHU. SO FAR THIS AFTERNOON WE HAVE RECEIVED ONE REPORT OF MODERATE
TURBULENCE...AND GFS FORECAST SOUNDINGS SHOW WINDS STRENGTHENING
FURTHER TONIGHT/MONDAY. THEREFORE WILL CONTINUE WITH THE AIRMET FOR
OCCASIONAL MODERATE LOW-LEVEL TURBULENCE IN THE LEE OF THE
MOUNTAINS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY THROUGH 6 PM HST MONDAY FOR SOUTH FACING SHORES
OF ALL ISLANDS.

SMALL CRAFT ADVISORY THROUGH 6 PM HST MONDAY FOR WATERS SOUTH OF THE
BIG ISLAND...MAALAEA BAY AND THE ALENUIHAHA AND PAILOLO CHANNELS.

&&

BRAVENDER