High Surf and Heavy Rain in Hawaii, March 13 to 15, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST FRI MAR 13 2009

.SYNOPSIS...
COOL NORTHWEST WINDS BEHIND A COLD FRONT WILL LAST THROUGH TONIGHT.
A LOW FAR TO THE NORTH WILL MOVE TO JUST NORTH OF KAUAI THIS
WEEKEND...LIKELY PRODUCING SOME UNSETTLED WEATHER THROUGH THE
SUNDAY...THEN TAPER OFF EARLY NEXT WEEK. TRADE WINDS ARE EXPECTED TO
RETURN DURING THE SECOND HALF OF THE WORK WEEK.

&&

.DISCUSSION...
THE DEEP LAYERED OCCLUDED LOW CURRENTLY ABOUT 384 NM NE OF THE STATE
IS STILL MOVING SW TOWARD THE ISLANDS. BASED ON POES AMSU AND SSM/I
DATA GUIDANCE APPEARS TO HAVE INITIALIZED FAIRLY WELL WITH RESPECT
TO THE LOW LEVEL MOISTURE FIELD ALONG WITH VARIOUS IMPULSE ROTATING
AROUND THE LOW ALSO NOTED IN THE WV IMAGERY. MODELS REMAIN IN GOOD
AGREEMENT BRINGING THE LOW TO ABOUT 300 NM NE OF HERE BEFORE
BEGINNING TO SLIDE IT W. A BAND OF MOISTURE SHOULD MAKE ITS WAY INTO
THE ISLANDS LATER THIS AFTERNOON GIVING WAY TO SLIGHTLY BETTER
SHOWER COVERAGE FOR OAHU AND KAUAI AS A WEAK IMPULSE MOVES OVER THE
AREA. WINDS ACROSS THE BIG ISLAND SUMMITS REMAIN STRONG AND WILL
LIKELY REMAIN THAT WAY THROUGH TOMORROW NIGHT. THERE ARE NO CHANGES
TO THE HIGH WIND WARNING AS OF NOW.

AS THE LOW PASSES N OF THE ISLANDS IT WILL SIGNIFICANTLY LOWER MID
LEVEL TEMPS AND 500 MG HEIGHTS. BY TONIGHT TIME SURFACE PWAT AND
DEWPOINTS WILL HAVE RISEN SLIGHTLY TO JUST OVER 1 INCH AND INTO THE
LOW 60S RESPECTIVELY. ANOTHER MORE POTENT IMPULSE LOOKS TO ROTATE
INTO THE AREA TONIGHT AROUND THE SW QUADRANT OF THE LOW. MODERATE
PVA AND BROAD SCALE LIFT ASSOCIATED WITH THE IMPULSE...ALONG WITH
700-500 MB LAPSE RATES ROUGHLY 6-6.5 C/KM WILL LIKELY TRIGGER A FEW
ISOLATED TSTORMS REGARDLESS OF COOLER SURFACE TEMPS AND UNIMPRESSIVE
BOUNDARY LAYER MOISTURE. THE HIGHEST CHANCES FOR THUNDER APPEAR TO
BE OVER THE FAR NW COASTAL ZONES RIGHT NOW...BUT HAVE ADDED SLIGHT
CHANCES TSTORMS TO THE GRIDS FOR OAHU/KAUAI TONIGHT INTO EARLY
TOMORROW MORNING GIVEN THE FAVORABLE DYNAMICS ALOFT. THIS WILL
LIKELY REQUIRE SOME FINE TUNING THROUGH TODAY AND TONIGHT GIVEN THE
UNCERTAINTIES IN THE DISTRIBUTION OF THE COLD POOL AND OTHER SMALLER
SCALE DETAILS. THE GRIDS HAVE BEEN AMENDED ACCORDINGLY.

THERE IS NO CHANGE IN THE LONG TERM REASONING FROM THE MID SHIFT.
WILL REVISIT THIS FOR THIS AFTERNOONS FORECAST PACKAGE.

&&

.PREVIOUS DISCUSSION ISSUED 400 AM HST...
THE COLD FRONT THAT PASSED THROUGH THE STATE A DAY OR TWO AGO HAS
FALLEN APART SOUTH OF THE BIG ISLAND...LEAVING BEHIND A BAND OF
BROKEN TO OVERCAST CLOUDS OVER THE WINDWARD COASTS AND SLOPES OF
MAUI AND THE BIG ISLAND. THIS IS A QUITE COMMON POST-FRONTAL CLOUD
FORMATION THAT CAN LAST FOR SEVERAL DAYS. ELSEWHERE...SKIES ARE
PARTLY CLOUDY. THIS PATTERN WITH MORE CLOUDS THAN BLUE SKIES SHOULD
LAST THROUGH TODAY AND MAYBE TONIGHT. AS FOR PRECIPITATION...LOW
AVAILABLE MOISTURE WILL LIMIT SHOWERS TO ISOLATED TO SCATTERED IN
COVERAGE AND LIGHT IN INTENSITY.

A LOW PRESENTLY CENTERED ABOUT 450 MILES NORTHEAST OF KAUAI WILL
MOVE TO THE SOUTHWEST ENDING UP JUST NORTH OR NORTHWEST OF KAUAI
THIS WEEKEND. THE CLOSE PROXIMITY OF THE LOW WILL LEAD TO A
DESTABILIZED ATMOSPHERE...ESPECIALLY OVER THE WESTERN HALF OF THE
ISLAND CHAIN. THE PRESENCE OF HEAVY SHOWERS AND THUNDERSTORMS WILL
HOWEVER DEPEND ON WHETHER THERE WILL BE ENOUGH MOISTURE AND WHERE
THE LOW WILL BE RELATIVE TO THE ISLANDS.

FOR NOW WE WILL STICK WITH A SOMEWHAT UNSETTLED WEATHER SCENARIO
THIS WEEKEND TAKING INTO ACCOUNT THE POSSIBILITY OF SHOWER BANDS
ROTATING COUNTERCLOCKWISE AROUND THE LOW AND ACROSS THE STATE. THERE
IS ALSO A CHANCE THAT CONVERGENT LOW LEVEL FLOW INTO THE LOW WILL
FOCUS SHOWER BANDS JUST ABOUT ANYWHERE OVER THE STATE. ALSO WITH
COLD AIR ALOFT THERE IS AN INCREASED CHANCE FOR THUNDERSTORMS TO
DEVELOP ESPECIALLY OVER THE WEST END OF THE ISLAND CHAIN AND OVER
WATERS NORTH AND NORTHWEST OF THE STATE. WE WILL HOLD OFF PUTTING
HEAVY SHOWERS AND/OR THUNDERSTORMS IN THE FORECAST UNTIL THERE IS
GREATER EVIDENCE THAT THEY WILL OCCUR.

THE LOW WILL WEAKEN TO AN OPEN TROUGH NEAR KAUAI BY TUESDAY AND WILL
PROBABLY TAKE ITS TIME FILLING. PROGS IN FACT WAIT UNTIL THE END OF
NEXT WEEK TO BRING BACK THE TRADES.

NORTHWEST WINDS OVER THE MAUNA KEA AND MAUNA LOA SUMMITS HAVE
INCREASED TO ABOVE 50 MPH...PROMPTING THE UPGRADE OF THE WIND
ADVISORY TO A HIGH WIND WARNING. THE STRONG MOUNTAIN TOP WINDS WILL
SWING AROUND TO THE SOUTHWEST THIS WEEKEND AND PERSIST THROUGH AT
LEAST TUESDAY.

&&

.MARINE...
THE LOW HAS PRODUCED A LARGE BUT RELATIVELY SHORT PERIOD NORTH SWELL
THAT WILL BUILD THROUGH THE DAY AND PEAK TONIGHT. THE SWELL COMBINED
WITH THE NORTH WINDS WILL PRODUCE STORMY CONDITIONS ALONG NORTH AND
EAST FACING SHORES. LARGE DISORGANIZED SURF CONTINUES TO IMPACT N
AND E FACING SHORES. SURF HEIGHTS ARE CHECKING IN SLIGHTLY HIGHER
THAN EXPECTED THIS MORNING SO NUMBERS HAVE BEEN ADJUSTED. THE
EXPIRATION TIME REMAINS THE SAME...6 PM TOMORROW. THE ASSOCIATED
ADVISORY WILL ALSO BE REVISED AND SENT WITH THE MORNING UPDATE.

THE NORTH SWELL AND WIND WAVES WILL LIKELY PRODUCE SURGES IN NORTH
FACING HARBORS SUCH AS THE KAHULUI AND HILO HARBORS TODAY THROUGH
SATURDAY. A MARINE WEATHER STATEMENT HAS BEEN ISSUED FOR THIS EVENT.

A SMALL CRAFT ADVISORY IS UP FOR ALL HAWAIIAN COASTAL WATERS FOR THE
COMBINED SEAS RELATED TO THE LARGE N SWELL...ALTHOUGH WINDS ARE
BORDERLINE FOR A FEW SELECT AREAS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST SATURDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU NORTH SHORE-OAHU KOOLAU-OLOMANA-
MOLOKAI-MAUI WINDWARD WEST-MAUI LEEWARD WEST-MAUI CENTRAL VALLEY-
WINDWARD HALEAKALA-BIG ISLAND NORTH AND EAST.

HIGH WIND WARNING UNTIL 6 AM HST SUNDAY FOR BIG ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR ALL HAWAIIAN
WATERS EXCEPT MAALAEA BAY-

&&

PUBLIC/MARINE...DEJESUS
DISCUSSION...CRAIG