High Surf Advisory 4, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
940 AM HST FRI JAN 14 2011

.SYNOPSIS...
TROPICAL MOISTURE AND REMNANT INSTABILITY WILL BRING SCATTERED
SHOWERS TO THE WESTERN ISLANDS TODAY WITH ISOLATED LIGHT SHOWERS
EXPECTED ELSEWHERE. A BRIEF HEAVY SHOWER REMAINS POSSIBLE. FAIR
WEATHER IS ON TAP FOR SATURDAY AND WITH ANOTHER COLD FRONT EXPECTED
CROSS THE STATE SUNDAY INTO MONDAY PRODUCING NUMEROUS SHOWERS AND
ISOLATED THUNDERSTORMS. SHOWERY CONDITIONS MAY LINGER INTO TUESDAY
WITH LIGHT EASTERLY FLOW AND WINDWARD SHOWERS RETURNING WEDNESDAY
THROUGH THE REMAINDER OF THE WORK WEEK.

&&

.DISCUSSION...
THE SHORT TERM FORECAST IS LOOKING MOSTLY ON TRACK TO GET THE DAY
SHIFT ROLLING THIS MORNING. WILL MAKE SOME MINOR TWEAKS TO THE POPS
OVER THE E PORTION OF THE STATE SO ANOTHER UPDATE WILL ACCOMPANY THE
AFD. RIDGING S OF THE ISLANDS IS MAINTAINING S FLOW ACROSS THE STATE
ALONG WITH GOOD TROPICAL MOISTURE ADVECTION. 14/12Z RAOBS AND
BLENDED TPW IMAGERY STILL INDICATING PWATS OF 1.5-1.8 INCHES. THERMO
PROFILES...MAINLY OVER THE W PORTION OF THE STATE REMAIN ON THE
UNSTABLE SIDE DESPITE SIGNS OF MID/LOW LEVEL WARMING. 88D RETURNS
REMAIN SCATTERED WITH A FEW ISOLATED MODERATE SHOWERS IMPACTING
KAUAI/OAHU. CONDITIONS STILL REMAIN FAVORABLE FOR AN ISOLATED HEAVY
SHOWER TODAY...ESPECIALLY OVER LAND AREAS IF SUFFICIENT ISOLATION
CAN FURTHER DESTABILIZE THE LOWER LEVELS. DEEP LAYERED 20-30KT S
FLOW SHOULD KEEP ANY ISOLATED HEAVY SHOWERS MOVING N AND
BRIEF...WHICH MINIMIZES OR ELIMINATES ANY FLOOD POTENTIAL TODAY.
OVERALL FRI SHOULD BE A FAIRLY TRANQUIL DAY WITH FURTHER IMPROVEMENT
FOR SAT AS THE AFOREMENTIONED RIDGE STRENGTHENS AND RELATIVELY DRIER
AIR NOSES IN FROM THE E.

GOES WV IMAGERY DEPICTS A STRONG ZONAL JET ALONG 3ON EXTENDING FROM
THE ASIAN COAST TO JUST N OF HAWAII. THIS IS MAINTAINING
PROGRESSIVE FLOW ACROSS MOST OF THE NPAC FOR NOW. DEEP LAYERED LOW
PRESSURE IS NEAR 35N173W MOVING NE WITH ITS ATTENDANT COLD FRONT
JUST OVER 700 NM WNW OF KAUAI THIS MORNING. THE FRONT WILL BE SLOW
MOVING TODAY AND SAT AS THE PARENT LOW LIFTS NE. THIS WILL PUT THE
FRONT ON KAUAIS DOORSTEP EARLY SUN MORNING. GUIDANCE REMAINS IN GOOD
AGREEMENT SHOWING SHARP SHORT WAVE AMPLIFICATION N OF THE STATE
BEGINNING SAT NIGHT. THIS WILL HELP NUDGE THE FRONT FURTHER E
FOLLOWED BY N/NW FLOW SUN INTO MON.

MODEL SOLUTIONS BEGIN TO DIVERGE MON. THE ECMWF/UKMET REMAIN IN GOOD
AGREEMENT AND SHOW GOOD CONTINUITY PINCHING OFF A POTENT MID LEVEL
LOW MON MORNING. THE 06Z GFS ALSO SUGGESTED THIS INITIALLY HOWEVER
THEN REMAINED PROGRESSIVE CARRYING THE LOW E WHILE LOSING AMPLITUDE.
THE 14/12Z GFS HAS SHOWN A MAJOR BREAK IN CONTINUITY TRENDING
TOWARDS THE OTHER GLOBAL GUIDANCE NOW DEPICTING A SIMILAR TIGHT
CLOSED LOW MOVING SLOWLY S. THE ECMWF CARRIES THE LOW OVER THE STATE
MON NIGHT THROUGH WED MORNING WHILE THE GFS REMAINS SLOWER WEAKER
AND FURTHER E. WITH RECENT GFS TRENDS AND ECMWF/UKMET CONTINUITY
WILL LIKELY TREND THE FORECAST FROM TUE ONWARD TOWARDS THE
ECMWF/UKMET WHICH WOULD BE SLIGHTLY WETTER MON-TUE FOR SOME OF
THE STATE.

THE REMAINDER OF THE FORECAST PERIOD IS LOOKING OK IN THE GRIDS. THE
STRONG ZONAL JET OFF ASIA THROUGH THE CENTRAL PACIFIC DOES SUPPORT
DOMINANT LOW PRESSURE OVER THE NWPAC. THIS IS SUGGESTIVE OF HIGHER
AMPLITUDE RIDGING DOWNSTREAM OVER THE ENPAC WHICH IS MORE IN LINE
WITH ECMWF SOLUTIONS IMPLYING E/ESE FLOW AND PASSING POCKETS OF
TROPICAL MOISTURE WED-FRI LOCALLY.

&&

.PREVIOUS DISCUSSION.../ISSUED 930 AM HST FRI MORNING/
RADAR IMAGERY INDICATES THAT THERE IS NOT MUCH SHOWER ACTIVITY OVER
THE STATE THIS MORNING. THE FRONT THAT BROUGHT THE ACTIVE WEATHER
OVER THE PAST COUPLE DAYS CONTINUES TO DISSIPATE AND LIFT TO THE
NORTHEAST...AND THERE ARE SIGNS THAT THE ATMOSPHERE IS BECOMING
SLIGHTLY MORE STABLE AS WELL. THE 12Z UPPER AIR SOUNDINGS AT LIHUE
AND HILO BOTH SHOW CAPPING INVERSIONS AT 7600 AND 6000 FEET
RESPECTIVELY...ALTHOUGH THEY ARE SOMEWHAT WEAK. THIS IS LIKELY
HELPING TO LIMIT SHOWER AND THUNDERSTORM DEVELOPMENT. WITH THE LACK
OF SHOWER ACTIVITY OVERNIGHT AND THE INCREASING STABILITY...THE
THREAT FOR WIDESPREAD HEAVY RAINS HAS ENDED...AND THUS THE FLASH
FLOOD WATCH FOR THE STATE HAS BEEN CANCELLED. HOWEVER...BRIEF
LOCALLY HEAVY SHOWERS TODAY CANNOT BE RULED OUT DUE TO THE OVERALL
INSTABILITY AND HIGH MOISTURE CONTENT OF THE
ATMOSPHERE...PARTICULARLY AROUND KAUAI COUNTY AND OAHU WHERE IT IS
SLIGHTLY MORE UNSTABLE AND MOIST THAN THE OTHER PARTS OF THE STATE.
NEVERTHELESS...WEATHER WILL CONTINUE TO IMPROVE TODAY AND SATURDAY
AS UPPER LEVEL RIDGING AND DRIER AIR MOVES OVER THE REGION.

OVER THE BIG ISLAND SUMMITS...A QUICK BURST OF SNOW IS POSSIBLE WITH
CONVECTION THIS MORNING. IN ADDITION...SPOTTER REPORTS FROM MAUNA
KEA AND WEB CAMS INDICATE THAT THERE HAD BEEN A LIGHT ICE
ACCUMULATION THROUGH THE DAY YESTERDAY. OVERNIGHT...INFRARED IMAGERY
SHOWED MID-LEVEL CLOUDS HANGING OVER THE SUMMITS...LIKELY PROVIDING
SOME SNOW...ALTHOUGH THOSE CLOUDS HAVE DISSIPATED OVER THE PAST 2
HOURS. WITH THE POSSIBILITY THAT ADDITIONAL MID-LEVEL CLOUDS WILL
MOVE ACROSS THE BIG ISLAND THIS MORNING...PROVIDING ADDITIONAL
SNOW...FREEZING DRIZZLE OR PATCHY LIGHT FREEZING RAIN...THE WINTER
WEATHER ADVISORY HAS BEEN EXTENDED THROUGH 10 AM THIS MORNING.

A 1030 MB SURFACE HIGH ABOUT 1870 MILES NORTHEAST OF OAHU CONTINUES
TO BRING MODERATE SOUTHERLY WINDS TO THE ISLANDS. WINDS WILL REMAIN
NEAR THIS DIRECTION AND SPEED THROUGH THIS AFTERNOON...WITH SHOWERS
FOCUSING OVER SOUTH FACING PORTIONS OF THE ISLANDS. WINDS WILL THEN
START TO WEAKEN SOMEWHAT AND BACK TO THE SOUTHEAST/EAST SOUTHEAST AS
THE HIGH MOVES SLIGHTLY TO THE NORTHWEST. WINDS WILL START TO VEER
AGAIN AS ANOTHER FRONT APPROACHES FROM THE NORTHWEST ON SUNDAY.

THIS NEW FRONT WILL BRING AN INCREASE IN SHOWERS TO THE ISLANDS
SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON AS IT MOVES DOWN THE
ISLAND CHAIN. AS THIS FRONT COMES THROUGH...AN UPPER LEVEL TROUGH
WILL DIG DOWN...BRINGING COLD 500 MB TEMPERATURES. THUS...THE
INSTABILITY AND MOISTURE WILL CREATE THE POSSIBILITY OF
THUNDERSTORMS WITH THE PASSAGE OF THE FRONT.

AFTER THE FRONTAL PASSAGE...ECMWF SHOWS A CUT-OFF UPPER LOW MOVING
DOWN FROM THE NORTH...AND EVENTUALLY MOVING OVER THE ISLANDS BY
WEDNESDAY. MEANWHILE...GFS ALSO SHOWS A CUT-OFF LOW FORMING BUT
STAYING SOUTH OF THE BIG ISLAND. BOTH MODELS INDICATE THE ATMOSPHERE
WILL BE RATHER DRY HOWEVER...WHICH WOULD BE AN INHIBITOR TO HEAVY
SHOWER/THUNDERSTORM DEVELOPMENT DURING THIS TIME.

&&

.MARINE...
MODEST OVERHEAD SURF EXPECTED ALONG EXPOSED N FACING SHORES THROUGH
SAT. THERE IS LARGE WNW SWELL EXPECTED SAT NIGHT POSSIBLY NEARING
WARNING LEVELS...BUT LIKELY AVERAGING AROUND THE 20 FT RANGE SUN
WITH ONLY MINOR UP/DOWN CHANGES THROUGH TUE. ANOTHER LARGER WNW
SWELL IS EXPECTED TO SHOW TUE NIGHT BUILDING WELL ABOVE WARNING
LEVELS OF 25 FT WED-THU GENERATED BY A LOW LATITUDE HURCN FORCE
SYSTEM WELL WNW OF THE STATE. THE SWELL WILL LIKELY WRAP INTO SOME S
FACING AREAS AND TRIGGER ADVISORIES ALONG THE LEEWARD BIG ISLAND AS
WELL. THE SURF WILL DROP SLOWLY AND REMAIN SIZEABLE THROUGH THE
REMAINDER OF THE WEEK. THESE SWELLS WILL TRIGGER HIGH SURF
ADVISORIES/WARNINGS ALONG WITH SMALL CRAFT ADVISORIES FOR OPEN OCEAN
SWELL HEIGHTS GREATER THEN 10 FT.

&&

.AVIATION...
MOSTLY VFR EXPECTED FOR THE TERMINALS TODAY. SCT SHRA/RA STILL
OCCURING OVER THE WRN PORTION OF THE STATE AND CSTL WTRS WITH ISOL
TCU TOPS FL200 WHERE THE ATMOSPHERE REMAINS UNSTABLE AND LLVL
MOISTURE IS ABUNDANT. MVFR COND STILL POSSIBLE OVER KAUAI/OAHU MT
WITH LOCAL IFR NEAR ANY STRONGER +RA THAT MAY DEVELOP THRU THE DAY.
CONDITIONS IMPROVE FURTHER OVERNIGHT AND INTO SAT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

PUBLIC/MARINE/AVIATION...DEJESUS
PREVIOUS...HARRISON