High Surf in Hawaii, September 18 to 22, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
859 AM HST TUE SEP 18 2007

.SYNOPSIS...PASSING TRADE WIND SHOWERS WILL AFFECT MAINLY THE
MOUNTAIN AND WINDWARD AREAS OF ISLANDS BUT A FEW SHOWERS WILL OCCUR
OVER THE LEEWARD SECTIONS MAINLY DURING NIGHT AND MORNINGS. BRISK
TRADE WINDS WILL WEAKEN A BIT FRIDAY AND SATURDAY.

&&

.DISCUSSION...A NARROW BAND OF MOISTURE IS RIDING ACROSS THE ISLANDS
THIS MORNING ON MODERATE TO LOCALLY FRESH TRADE WINDS. THE MAIN
HAWAIIAN ISLANDS WERE UNDERNEATH DIFFLUENT FLOW ALOFT AT THE EXIT
REGION OF AN UPPER LEVEL JET. THESE TWO FEATURES WERE WORKING
TOGETHER TO MAKE IT A LITTLE MORE SHOWERY THIS MORNING...ESPECIALLY
FOR WINDWARD AND MAUKA SECTIONS. HAVE UPDATED THE GRIDS A BIT FOR
MORE CLOUDS AND SHOWERS FOR TODAY. THE BAND OF MOISTURE SHOULD CLEAR
THE ISLANDS LATER THIS AFTERNOON OR THIS EVENING. REST OF THE
FORECAST REMAINS THE SAME AND PREVIOUS DISCUSSION FOLLOWS.

&&

.PREV DISCUSSION...FROM 327 AM...THE SURFACE HIGH FAR TO THE
NORTHEAST WILL STRENGTHEN THROUGH THURSDAY REACHING THE 1030 TO 1035
MB RANGE. TRADE WINDS WILL GENERALLY BE FROM 15 TO 20 MPH...AND TO
25 MPH OVER WINDIER LOCALES.

THE UPPER ATMOSPHERIC LOW...STILL ABOUT 700 MILES NORTH NORTHWEST
BUT NOT READILY APPARENT ON WATER VAPOR IMAGERY... WILL SHIFT BACK
TO BE A LITTLE LESS THAN 400 MILES WEST NORTHWEST OF KAUAI ON
THURSDAY. UPPER CLOUDINESS FROM AN AREA OF CONVECTION PRESENTLY
BETWEEN KAUAI AND THE INTERNATIONAL DATELINE WILL BE SWEPT OVER THE
ISLANDS BY THIS UPPER LOW BEGINNING EARLY WEDNESDAY. THE STRONG
SURFACE HIGH WILL EVIDENTLY PREVENT THIS UPPER LOW FROM DRAWING UP A
SIGNIFICANT FLOW OF MOISTURE FROM THE SOUTH. THERE MAY BE HOWEVER
BE A RESULTING INCREASE IN TRADE WIND SHOWERS ON THURSDAY.
PRECIPITATION AMOUNTS ARE NOT EXPECTED TO BE LARGE. THE UPPER LOW
BEGINS TO LIFT NORTHWARD LATE FRIDAY. ANOTHER EFFECT OF THIS UPPER
LOW WILL BE THE WEAKENING OF THE SURFACE PRESSURE GRADIENT OVER THE
STATE...HENCE SOME DECREASE IN TRADES FRIDAY AND SATURDAY...THEN
BACK TO MODERATE STRENGTH TRADES ON SUNDAY.

&&

.MARINE...SMALL CRAFT ADVISORIES REMAIN IN EFFECT FOR THE ALENUIHAHA
AND PAILOLO CHANNELS AS WELL AS MAALAEA BAY AND WATERS SOUTH OF THE
BIG ISLAND. ANOTHER MODERATE SOUTH SWELL IS EXPECTED WEDNESDAY AND A
MODERATE NORTHWEST SWELL ARRIVING LATE THURSDAY FROM A STORM THAT
MOVED TOWARD THE WESTERN ALEUTIAN ISLANDS 2 DAYS AGO. SURF SHOULD BE
LESS THAN ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...SMALL CRAFT ADVISORY FOR PAILOLO
CHANNEL...MAALAEA BAY...ALENUIHAHA CHANNEL...BIG ISLAND LEEWARD AND
BIG ISLAND SOUTHEAST WATERS THROUGH THURSDAY.

&&

R BALLARD