High Surf in Hawaii, November 9 to 11, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT NOV 9 2013

.SYNOPSIS...
A COLD UPPER LEVEL TROUGH AND A MOIST AIRMASS WILL LEAD TO UNSTABLE
CONDITIONS AND THE POTENTIAL FOR HEAVY RAIN ACROSS THE STATE THIS
WEEKEND. CONDITIONS WILL BE MOST UNSTABLE ACROSS KAUAI AND OAHU...
WHERE THERE IS A SLIGHT CHANCE OF THUNDERSTORMS. A SHEAR LINE NORTH
OF THE AREA WILL MOVE SOUTH THROUGH SUNDAY NIGHT...BRINGING AN
INCREASE IN SHOWERS AND STRONGER NORTHEASTERLY WINDS. WINDS AND
RAIN WILL DIMINISH BY MID-WEEK...ALTHOUGH WE MAY SEE AN INCREASE IN
SHOWERS AGAIN LATE IN THE WEEK.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL TROUGH AXIS NEAR KAUAI
ORIENTED NEARLY EAST TO WEST. THIS TROUGH IS MOVING SOUTHEAST
SLOWLY. A STRONGER SHORTWAVE IS LOCATED ALMOST 600 MILES NORTH OF
KAUAI. THIS TROUGH IS MOVING TO THE SOUTH AT 20 MPH. AT THE
SURFACE...A SHEAR LINE IS LOCATED ABOUT 150 MILES NORTH OF KAUAI.
THE CLOUDS ASSOCIATED WITH THE SHEAR LINE HAVE A RAGGED APPEARANCE
ON SATELLITE IMAGERY. A SECOND SURFACE BOUNDARY IS LOCATED OVER 500
MILES NORTH OF KAUAI. THE 12Z SOUNDING FROM LIHUE SHOWS A WEAK
INVERSION NEAR 12KFT...BUT NOT ENOUGH TO INHIBIT DEEP CONVECTION. A
MODIFIED SOUNDING FOR 79/69 YIELDS ABOUT 1500 J/KG OF CAPE. THE HILO
SOUNDING SHOWS MUCH WARMER LOW/MID-LEVEL TEMPERATURES...AND ALSO
LOWER MOISTURE DEPTH...ONLY UP TO 5KFT. PRECIPITABLE WATERS RANGE
FROM 1.5 INCHES IN LIHUE TO 1.3 INCHES IN HILO...BUT THE AIRMASS IS
ACTUALLY MORE DIFFERENT THAN THAT WOULD INDICATE. THICK MID-HIGH
LEVEL CLOUDS SOUTHEAST OF THE UPPER TROUGH ARE LOCATED NEAR THE BIG
ISLAND...AND ARE CONTRIBUTING MORE TO THE PRECIPITABLE WATER
CALCULATION. THE HILO SOUNDING SHOWS A DRY LAYER BETWEEN 5KFT-10KFT.

THE UPPER TROUGH NEAR KAUAI WILL BE REINFORCED BY THE NEXT TROUGH
DIGGING SOUTHWARD. IN THE NEAR TERM...CONDITIONS REMAIN UNSTABLE...
ESPECIALLY ACROSS THE WESTERN HALF OF THE STATE. WE HAVE RECEIVED
RAINFALL REPORTS OF OVER 1 INCH PER HOUR FROM RAIN GAGES ON KAUAI
AND OAHU THIS MORNING...AND THIS ACTIVITY IS EXPECTED TO CONTINUE
WITH THE UPPER TROUGH REMAINING OVERHEAD. THERE MAY BE A DIMINISHING
TREND IN ACTIVITY DURING THE AFTERNOON DUE TO DIURNAL PROCESSES.
HOWEVER...GIVEN THE DEEP CONVECTION FLARING UP WITHIN 150 MILES
NORTH OF KAUAI...THERE APPEARS TO BE AMPLE UPPER LEVEL SUPPORT NEAR
THE TROUGH TO MAINTAIN THE MENTION OF LOCALLY HEAVY RAINFALL
THROUGH THE DAY.

THE SECOND SHORTWAVE CURRENTLY NEAR 30N IS EXPECTED TO DIG SOUTHWARD
TO KAUAI TONIGHT. THIS IMPULSE WILL PROVIDE ADDITIONAL UPPER LEVEL
SUPPORT FOR AN AIRMASS THAT IS ALREADY UNSTABLE. IT WILL ALSO HELP
TO PROPEL THE SHEAR LINE CURRENTLY TO OUR NORTH DOWN ACROSS THE
ISLANDS...ENHANCING THE AMOUNT OF LOW-LEVEL MOISTURE. WHILE THE
BOUNDARY MAY PROVIDE A LOW-LEVEL FOCUS FOR CONVECTIVE DEVELOPMENT...
THE 12Z GFS AND ECMWF SHOW IT WEAKENING AS IT MOVES ACROSS THE
STATE. THIS SEEMS REASONABLE GIVEN THE INCREASINGLY RAGGED
APPEARANCE TO THE CLOUD FEATURES ASSOCIATED WITH IT. HOWEVER...
CONSIDERING THE CONVECTIVE FLAREUPS AND LOCALIZED HEAVY RAINS THAT
WE HAVE BEEN SEEING THIS MORNING...THERE IS THE POTENTIAL FOR MORE
WIDESPREAD HEAVY RAINS TONIGHT THAT MAY REQUIRE A FLASH FLOOD WATCH.
IF HEAVY RAIN DOES DEVELOP...IT WOULD BE FOCUSED PRIMARILY ALONG
WINDWARD SECTIONS. STRONG NORTHEASTERLY WINDS WILL DEVELOP ACROSS
THE STATE BEHIND THE SHEAR LINE.

INTO THE EXTENDED FORECAST...THERE IS A GENERAL CONSENSUS BETWEEN
THE GFS/ECMWF/CANADIAN/NAVGEM WITH RESPECT TO THE GENERAL PATTERN...
SHOWING A CUTOFF LOW DEVELOPING FAR NORTHEAST OF THE STATE AND
RETROGRADING WESTWARD AS ADDITIONAL ENERGY DIGS INTO THE BACKSIDE OF
THE LOW. HOWEVER...DIFFERENCES PERSIST WITH THE TIMING AND PLACEMENT
OF INDIVIDUAL FEATURES...SO THE EXTENDED WILL CONTINUE TO FEATURE
MORE OF A BROAD-BRUSHED PATTERN. DESPITE A 1050MB HIGH DEVELOPING
FAR NORTH-NORTHWEST OF THE STATE LATE SUNDAY /A STRENGTH WHICH THE
MODELS HAVE BEEN CONSISTENT WITH FOR MOST OF THE PAST WEEK/...A
DEVELOPING SURFACE WAVE NORTH OF THE STATE WILL KEEP US SOMEWHAT
SEPARATED FROM THE STRONGEST PERSISTENT WINDS. BY MONDAY INTO
TUESDAY...WINDS WILL START TO WEAKEN AS THE LOW TO OUR NORTH
NORTHEAST STRENGTHENS AND SHIFTS THE RIDGE SOUTHWARD TOWARDS THE
ISLANDS. A BRIEF PERIOD OF DRIER LOW-LEVEL AIR IS EXPECTED MID-WEEK
BEHIND THE SHEAR LINE. HOWEVER...BOTH THE GFS AND ECMWF SHOW A WEAK
INVERTED TROUGH DEVELOPING NEAR THE STATE LATE IN THE WEEK AS A NEW
UPPER LEVEL TROUGH DIGS DOWN TO OUR LATITUDE. THIS SYSTEM MAY BRING
AN INCREASE IN MOISTURE FROM THE SOUTHEAST...LEADING TO ANOTHER
PERIOD OF WET WEATHER LATE IN THE NEW WEEK.

&&

.AVIATION...
CLOUDS AND SHOWERS COMING IN FROM THE EAST MAY PRODUCE SOME BRIEF
MVFR CONDITIONS OVER WINDWARD SLOPES AND ADJACENT WATERS BUT MOST
TAF SITES SHOULD HAVE PREVAILING VFR CONDITIONS.

THERE IS ALSO A SLIGHT CHANCE THAT A THUNDERSTORM OR TWO COULD FORM
IN THE AREA TODAY.

&&

.MARINE...
TRADE WINDS ARE ALREADY BEGINNING TO GRADUALLY INCREASE TODAY. THE
ASCAT PASS OVERNIGHT SHOWED WINDS OF 25 KT IN THE ALENUIHAHA
CHANNEL. ALSO...THE HANALEI AND WAIMEA BAY BUOYS HAVE BEEN REPORTING
SIGNIFICANT WAVE HEIGHTS ABOVE 10 FEET...WHICH IS AT LEAST 2 FEET
HIGHER THAN THE GUIDANCE FROM THE WAVE WATCH III MODEL. A SMALL
CRAFT ADVISORY IS IN EFFECT FOR PORTIONS OF THE COASTAL WATERS.
THESE CONDITIONS WILL SPREAD TO ALL COASTAL WATERS AS WINDS AND SEAS
INCREASE WITH THE APPROACH OF THE SHEAR LINE TO OUR NORTH. TRADE
WIND SPEEDS MAY APPROACH GALE FORCE OVER SOME PARTS OF THE COASTAL
WATERS FROM SUNDAY INTO MONDAY. EXPECT THE TRADES TO GRADUALLY TAPER
OFF MONDAY INTO TUESDAY.

INCREASING NORTH AND NORTHWEST SWELLS WILL PRODUCE LARGER SURF ALONG
EXPOSED NORTH FACING SHORES OF MOST ISLANDS THROUGH THIS EVENING. A
LARGE...SHORT-PERIOD NORTH NORTHEAST SWELL IS EXPECTED TO BUILD FROM
TONIGHT THROUGH SUNDAY. THIS SWELL WILL LIKELY PRODUCE SURF HEIGHTS
NEAR THE HIGH SURF ADVISORY THRESHOLDS ALONG EXPOSED NORTH AND EAST
FACING SHORES OF THE ISLANDS FROM SUNDAY INTO MONDAY...AND MAY ALSO
CAUSE PROBLEMS WITH SURGES IN NORTH FACING HARBORS.

ANOTHER SIGNIFICANT NORTH SWELL ARRIVING TUESDAY NIGHT WILL LIKELY
BUILD WELL ABOVE THE HIGH SURF ADVISORY THRESHOLD ALONG NORTH FACING
SHORES ON WEDNESDAY. IN FACT...SURF ALONG NORTH FACING SHORES MAY
APPROACH THE HIGH SURF WARNING CRITERIA WEDNESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM HST SUNDAY
FOR BIG ISLAND WINDWARD WATERS-BIG ISLAND LEEWARD WATERS.

SMALL CRAFT ADVISORY FROM 6 AM THIS MORNING TO 6 PM HST SUNDAY
FOR KAUAI NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-KAIWI CHANNEL-MAUI COUNTY LEEWARD WATERS-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM HST SUNDAY
FOR OAHU LEEWARD WATERS-MAALAEA BAY.

SMALL CRAFT ADVISORY FROM NOON TODAY TO 6 PM HST SUNDAY FOR
KAUAI LEEWARD WATERS-MAUI COUNTY WINDWARD WATERS.

&&

PUBLIC...BRAVENDER
MARINE...HOUSTON/BRAVENDER
AVIATION...BURKE