Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 020231
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST TUE SEP 1 2015

.SYNOPSIS...
VERY HUMID CONDITIONS WITH SPOTTY HEAVY SHOWERS...MAINLY EACH
AFTERNOON...WILL CONTINUE THROUGH MOST OF THE WEEK. WINDS WILL TURN
SOUTHERLY FOR MUCH OF THE WEEK...THEN BECOME LIGHT AND VARIABLE LATE
IN THE WEEK. THE EXTENDED FORECAST WILL DEPEND HEAVILY ON THE TRACK
OF HURRICANE JIMENA WELL NORTHEAST OF THE STATE...BUT A BRIEF RETURN
TO DRIER EASTERLY WINDS IS POSSIBLE EARLY NEXT WEEK.

&&

.DISCUSSION...
HURRICANE IGNACIO IS LOCATED LESS THAN 300 MILES NORTHEAST OF THE
STATE...WITH OUTER RAIN BANDS ASSOCIATED WITH IT APPARENT ON RADAR
APPROACHING THE WINDWARD COASTAL WATERS. WATER VAPOR IMAGERY SHOWS A
HIGH WEST OF THE STATE WITH A TROUGH TO THE NORTHWEST. A SURFACE
HIGH IS LOCATED FAR NORTH OF THE STATE...THOUGH IGNACIO INTERRUPTS
THE GRADIENT BETWEEN US AND THE HIGH. 00Z SOUNDINGS SHOW
PRECIPITABLE WATERS RANGING FROM 1.67 INCHES IN LIHUE TO 2.00 INCHES
IN HILO. A WEAK INVERSION IS ALSO NOTED NEAR 14KFT AT LIHUE...WITH
DRIER AIR ABOVE. EARLY AFTERNOON MIMIC TOTAL PRECIPITABLE WATER
IMAGERY IS TOO MOIST COMPARED TO THE SOUNDINGS...BUT DOES SHOW
QUALITATIVELY SLIGHTLY DRIER AIR OVER THE SMALLER ISLANDS...WITH A
BAND OF HIGHER MOISTURE NEAR THE BIG ISLAND AND ALSO NORTHEAST NEAR
IGNACIO.

THE DRIER AIR AND WEAK ELEVATED INVERSION OVER THE SMALLER ISLANDS
ARE PROBABLY RELATED TO SUBSIDENCE OUTSIDE OF IGNACIO. THIS HAS
HELPED TO LIMITED CLOUDS AND SHOWERS ACROSS THE SMALLER
ISLANDS...THOUGH SOME MOISTURE BANDS IS STARTING TO APPROACH KAUAI
AND OAHU. RAINFALL AMOUNTS HAVE BEEN LIMITED THIS AFTERNOON...WITH
TOTALS GENERALLY A QUARTER INCH OF LESS. HEAVY SHOWERS/THUNDERSTORMS
ONLY FORMED ACROSS THE INTERIOR AND SOUTHEAST-EAST SECTIONS OF THE
BIG ISLAND...WELL INTO THE HIGHER MOISTURE PLUME AND UNSTABLE AIR.
THIS CONVECTION WILL DIMINISH WITH SUNSET. THE LARGE SCALE LOW-LEVEL
FLOW HAS CONTINUED TO BACK THROUGH THE DAY...WITH NORTH WINDS ON
THE KAUAI VAD WIND PROFILE...NORTHWEST ON THE MOLOKAI VWP...AND
SOUTHWEST ON THE KOHALA AND SOUTH BIG ISLAND RADARS. THIS WIND
PATTERN MAY SETUP A CONVERGENCE BAND TO THE WEST OF THE BIG ISLAND
THAT MAY ENHANCE CLOUDS/SHOWERS ACROSS WHAT WOULD NORMALLY BE
LEEWARD SECTIONS OF MAUI AND THE BIG ISLAND.

ASIDE FROM THE HEAVY RAIN AND THUNDERSTORM THREAT...ANOTHER CONCERN
WILL BE THE VERY HUMID CONDITIONS. THE ISLANDS ARE LOCKED UNDER A
TROPICAL AIRMASS WITH DEW POINTS HOVERING IN THE MID 70S TO EVEN THE
UPPER 70S AT TIMES. WHILE MAX TEMPS WILL BE NEAR TO SLIGHTLY ABOVE
NORMAL...THE HUMIDITY WILL CREATE HEAT INDEX VALUES IN THE VERY
UNCOMFORTABLE RANGE OF THE UPPER 90S...AND OVERNIGHT TEMPS WILL
STRUGGLE TO GET BELOW THE UPPER 70S.

IGNACIO IS FORECAST TO LIFT NORTH OF THE STATE WEDNESDAY THROUGH
FRIDAY...BRINGING AN EXTENDED RUN OF VERY HUMID CONDITIONS AND
SPOTTY LOCALLY HEAVY SHOWERS. SIMILAR TEMPS AND HUMIDITY CONDITIONS
WILL HOLD INTO SATURDAY AS LIGHT SOUTHERLY WINDS OFFER NO RELIEF.
THE ATMOSPHERE WILL REMAIN MOIST THROUGH A DEEP LAYER AS
PRECIPITABLE WATER HOLDS IN THE 1.75 TO 2 INCH RANGE. THE ATMOSPHERE
WILL CONTINUE TO BE SOMEWHAT UNSTABLE WITH NO INVERSION AS AN UPPER
LEVEL TROUGH REMAINS OVER OR JUST WEST OF THE ISLANDS. AS A
RESULT...LOCALLY HEAVY SHOWERS WILL BE POSSIBLE...AND WE WILL HAVE
TO WATCH FOR THE POSSIBILITY OF A DEVELOPING CONVERGENCE ZONE
PRODUCING MORE ORGANIZED HEAVY RAINFALL OVER PORTIONS OF THE STATE
ON WEDNESDAY AND THURSDAY. HEAVY SHOWERS WERE LEFT OUT OF THE
FORECAST AFTER THURSDAY AS RIDGING ALOFT BEGINS TO WORK ITS WAY OVER
THE ISLANDS FROM THE EAST.

DRIER EASTERLY FLOW MAY DEVELOP EARLY NEXT WEEK...BUT CONFIDENCE
REMAINS LOW IN THE EXTENDED. THIS IS MAINLY DUE TO UNCERTAINTY
REGARDING THE EVOLUTION OF HURRICANE JIMENA...WHICH IS FORECAST TO
GRADUALLY TRACK FAR EAST AND NORTHEAST OF THE STATE.

&&

.AVIATION...
SEE TC SIGMET SERIES TANGO FOR TROPICAL CYCLONE IGNACIO.

SMALLER ISLANDS HAVE REMAINED FAIRLY QUITE THIS AFTERNOON...WITH
ONLY ISOLATED TO SCATTERED SHOWERS. THE BIG ISLAND ON THE OVERHAND
HAS SEEN THUNDERSTORMS PULSE UP AROUND THE ISLAND WITH HIGHEST
CONCENTRATION JUST SOUTH OF HILO NEAR MOUNTAIN VIEW. CB TOPS ON
THESE THUNDERSTORMS WERE REACHING TOPS NEAR FL400. AIRMET SIERRA IS
POSTED FOR MOUNTAIN OBSCURATION ON THE EAST SIDE OF THE BIG ISLAND.
THE PULSE-TYPE THUNDERSTORM ACTIVITY SHOULD BEGIN TO DIMINISH WITH
SUNSET AND THE AIRMET WILL LIKELY BE CANCELLED.

OVERNIGHT THUNDERSTORM THREAT IS LIKELY TO REMAIN MINIMAL...EXCEPT
IN THE FAR NORTHERN COASTAL WATERS NEAR IGNACIO. A SCATTERED TO
NUMEROUS SHOWERS AREA MORE LIKELY OVER THE WESTERN HALF OF THE
STATE AS IGNACIO MOVES NW.

&&

.MARINE...
THE LARGE SWELL FROM HURRICANE IGNACIO CAUSED PROBLEMS IN A NUMBER
OF LOCATIONS...WITH DEBRIS WASHED ACROSS ROADS ON THE BIG ISLAND AND
OAHU AND REPORTS OF UP TO 20 FOOT SURF ALONG EAST FACING SHORES OF
KAUAI. THIS SWELL HAS BACKED MORE NORTHERLY THROUGH THE DAY AND ALSO
LOWERED IN HEIGHT AND PERIOD...AS IGNACIO IS PASSING NORTH OF THE
STATE. SEAS AT NORTHERN AND WINDWARD CDIP BUOYS HAVE LOWER TO 8-10
FEET THIS AFTERNOON...BUT A NEW EASTERLY SWELL FROM HURRICANE JIMENA
SHOULD FILL IN SHORTLY. THIS SWELL WILL TAKE US BACK TO 090/100
DEGREE DIRECTION...WHICH WILL IMPACT SOUTHEAST SECTIONS OF THE BIG
ISLAND AND MAUI MOST DIRECTLY. WAVEWATCH GUIDANCE SHOWS THIS SWELL
BUILDING THROUGH THE NIGHT...PEAKING WEDNESDAY/WEDNESDAY NIGHT AND
REMAINING STEADY THROUGH THURSDAY. LATE IN THE WEEK...WE SHOULD SEE
THE DIRECTION START TO BACK TO A MORE EAST-NORTHEAST DIRECTION AS
JIMENA GAINS MORE LATITUDE...AND EVEN SEE AN INCREASE IN HEIGHT AS
IT MOVES CLOSER TO THE STATE. BECAUSE OF THE NEW SWELL...WE HAVE
EXTENDED THE HIGH SURF WARNING. THE NEW WARNING RUNS THROUGH
THURSDAY...BUT WE COULD EVENTUALLY END UP EXTENDING THROUGH THE
WEEKEND OR LONGER.

A SMALL CRAFT ADVISORY IS ALSO IN EFFECT THROUGH THURSDAY FOR
HAZARDOUS SEAS DUE TO THE SWELLS FROM IGNACIO AND JIMENA. THIS
ADVISORY MAY ALSO NEED TO BE EXTENDED THROUGH THE WEEKEND OR LONGER
AS SEAS REMAIN ELEVATED. WINDS ARE EXPECTED TO REMAIN BELOW ADVISORY
LEVELS THIS WEEK.

LONG-PERIOD SWELLS FROM THE SOUTH-SOUTHWEST MAY PRODUCE
ADVISORY-LEVEL SURF ALONG SOUTH-FACING SHORES THIS WEEKEND. PLEASE
REFER TO THE LATEST COLLABORATIVE NEARSHORE SWELL AND WIND
FORECAST /SRDHFO/ FOR MORE DETAILS ON THE SWELLS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 PM HST THURSDAY FOR EAST FACING SHORES OF
KAUAI...OAHU...MOLOKAI...MAUI...AND THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-OAHU WINDWARD WATERS-
KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-PAILOLO CHANNEL-ALENUIHAHA
CHANNEL-BIG ISLAND WINDWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

$$

PUBLIC/MARINE...BRAVENDER
AVIATION...EATON




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