High Surf in Hawaii, November 27 to 28, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI NOV 27 2009

.SYNOPSIS...
STRONG TRADE WINDS WILL DIMINISH INTO THE WEEKEND AS WINDWARD
SHOWERS BECOME LESS INTENSE. BY SUNDAY EVENING...A FRONT
APPROACHING FROM THE NORTHWEST WILL WEAKEN THE TRADES FURTHER...
WHILE INTENSIFYING SHOWERS BY GATHERING MOISTURE FROM THE SOUTHEAST.
MORE TYPICAL TRADE-WIND CONDITIONS WILL RETURN BY MID-WEEK.

&&

.DISCUSSION...
WITH SURFACE HIGH PRESSURE PERSISTING TO THE NORTH...THE TRADE WINDS
REMAINED UNUSUALLY STRONG ACROSS THE MAIN HAWAIIAN ISLANDS. SURFACE
DATA FROM AROUND THE STATE VARIED CONSIDERABLY IN SUSTAINED WIND
SPEED...AND EVEN MORE IN GUSTS...BUT THE OVERALL WIND SPEED FELL
JUST SHORT OF THE THRESHOLD FOR A WIND ADVISORY. STILL...PRESSURE
TRENDS REMAINED COMPARABLE TO THOSE OF THE PAST FEW DAYS...SO THIS
ADVISORY POSSIBLY MAY BE NEEDED AT SOME POINT LATER TODAY. AFTER
TONIGHT THOUGH...WIND SPEED SHOULD DIMINISH NOTICEABLY. BY WAY OF
CONTRAST...THE LOWER WIND-SPEED THRESHOLD FOR A SMALL CRAFT
ADVISORY REQUIRED IT TO BE IN EFFECT FOR ALL THE COASTAL WATERS.

IN TERMS OF RAINFALL...THE STRONG TRADES CONTINUED TO CARRY PASSING
SHOWERS OVER THE SMALLER ISLANDS...ENHANCING RAINFALL FURTHER ALONG
WINDWARD SLOPES. ALTHOUGH THE MID-LEVEL TROUGH OVER THE STATE HAD
BEGUN TO LIFT OUT TO THE NORTHEAST...ENOUGH OF THE COLD POOL ALOFT
AND DYNAMIC INSTABILITY REMAINED TO KEEP THE AIR MASS LESS STABLE
THAN IS USUAL. THE RELATIVELY DRY 12Z SOUNDING WITH A PARTIALLY
REFORMED INVERSION AT LIHUE CONTRASTED SIGNIFICANTLY WITH THE MUCH
MOISTER PROFILE AT HILO...THOUGH BOTH WERE ONLY MODESTLY UNSTABLE
EVEN WITH COLD TEMPERATURES ALOFT.

THE AXIS OF THE JET STREAM ASSOCIATED WITH THE TROUGH INTERACTED
WITH THE LOW-LEVEL MOISTURE EARLIER IN THE NIGHT TO PRODUCE TRAINING
THUNDERSTORM CELLS OVER EAST MAUI...BUT AS THE AXIS SHIFTED FURTHER
EAST...THIS ACTIVITY MOVED OVER THE WINDWARD WATERS AND COAST OF THE
BIG ISLAND. AS THE AXIS CONTINUES TO MOVE EAST OVER THE NEXT FEW
HOURS...THE BIG ISLAND SHOULD START TO DRY OUT AS WELL.

GUIDANCE GENERALLY FAVORS PROGRESSIVE SOLUTIONS THROUGH THE FORECAST
PERIOD...WITH SYNOPTIC SYSTEMS MOVING ACROSS THE NORTH PACIFIC
FAIRLY STEADILY. BY SUNDAY EVENING...ANOTHER MID-LEVEL DISTURBANCE
IS EXPECTED TO ARRIVE OVER THE STATE AND DEEPEN TOWARD THE SOUTH...
DRAGGING A FRONT TOWARD THE ISLANDS. AT THIS POINT...IT DOES NOT
LOOK LIKE THE TRADES WILL GO AWAY COMPLETELY AS THE FRONT DISRUPTS
THE SUBTROPICAL HIGH...BUT THE TRADES WILL WEAKEN AND DEVELOP A
SLIGHT SOUTHEASTERLY TILT. RAINFALL WILL BE ENHANCED AS WELL...
MAINLY IN THE FORM OF PRE-FRONTAL SHOWERS FROM SUNDAY AFTERNOON INTO
THE NIGHT.

THIS INCREASE IN SHOWERS LIKELY WILL END BY WEDNESDAY AS THE LOW
LIFTS OUT AGAIN...AND HIGH PRESSURE REESTABLISHES ITSELF BOTH ALOFT
AND AT THE SURFACE TO THE NORTH. MODERATE TRADES ARE EXPECTED TO
RETURN BY THE MIDDLE OF NEXT WEEK WITH MORE TYPICAL TRADE-WIND
SHOWERS...ONLY TO BE DISPLACED BY MORE WIDESPREAD SOUTHEASTERLIES
AHEAD OF AN OSTENSIBLY STRONGER FRONT APPROACHING THE STATE BY NEXT
WEEKEND.

&&

.MARINE...
AS THE SWELL TURNS MORE NORTHERLY TODAY...IT IS EXPECTED TO SHIFT
ADVISORY-LEVEL SURF TO EAST-FACING SHORES OF MOST ISLANDS. THE
ELEVATED EAST SURF IS EXPECTED TO LAST AT LEAST THROUGH EARLY
SUNDAY. A NEW NORTHWEST SWELL WILL ARRIVE EARLY ON SATURDAY...
BOOSTING SURF HEIGHTS TO NEAR THE ADVISORY LEVEL ALONG NORTH SHORES.

A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ALL COASTAL WATERS FOR
A COMBINATION OF HIGH SEAS AND STRONG TRADE WINDS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR NIIHAU-KAUAI
WINDWARD-OAHU KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
WINDWARD WATERS-KAUAI LEEWARD WATERS-OAHU WINDWARD WATERS-OAHU
LEEWARD WATERS-MAUI COUNTY WINDWARD WATERS-MAUI COUNTY LEEWARD
WATERS-MAALAEA BAY-BIG ISLAND WINDWARD WATERS-BIG ISLAND LEEWARD
WATERS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI CHANNEL-KAIWI CHANNEL-PAILOLO CHANNEL-ALENUIHAHA
CHANNEL-BIG ISLAND SOUTHEAST WATERS.

&&

RYSHKO