Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 210203
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST MON OCT 20 2014

.SYNOPSIS...
WIDESPREAD RAIN HAS TAPERED OFF AS TROPICAL STORM ANA MOVES FARTHER
AWAY FROM THE STATE...LEAVING BEHIND LIGHTER SHOWERS NEAR KAUAI AND
THICK HIGH CLOUDS AS FAR AS OAHU. MODERATE TRADE WINDS WILL FOCUS
SHOWERS ACROSS EASTERN SECTIONS OF THE ISLANDS TONIGHT...THEN BECOME
LIGHTER FROM TUESDAY THROUGH THE END OF THE WEEK. A BAND OF MOISTURE
ASSOCIATED WITH AN OLD FRONT NORTHEAST OF THE STATE WILL ENHANCE
RAINFALL TUESDAY NIGHT AND WEDNESDAY.

&&

.DISCUSSION...
AT 2 PM HST...TROPICAL STORM ANA WAS LOCATED 320 MILES
WEST-SOUTHWEST OF LIHUE...AND IS MOVING TO THE WEST AT 7 MPH.
CURRENT RADAR IMAGERY SHOWS HEAVY RAIN HAS MOVED WEST OF THE COASTAL
WATERS...WITH STEADY LIGHT TO WITH EMBEDDED MODERATE SHOWERS NEAR
KAUAI AND NIIHAU. ELSEWHERE ACROSS THE STATE SHOWERS ARE FOLLOWING A
MORE TYPICAL TRADE WIND PATTERN...WITH LIGHT RAIN ACROSS WINDWARD
AND MAUKA SECTIONS. A THICK LAYER OF MIDDLE AND HIGH LEVEL CLOUDS
EXTENDS FROM ANA ACROSS MUCH OF KAUAI AND OAHU...AND WILL KEEP SKIES
CLOUDY ACROSS THESE ISLANDS THROUGH THE NIGHT.

WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL HIGH NORTH AND NORTHWEST OF
THE STATE...WITH A TROUGH FAR TO THE NORTHEAST. ANA IS LOCATED SOUTH
OF THE HIGH...AND CONTINUES MOVING TO THE WEST AWAY FROM THE MAIN
HAWAIIAN ISLANDS. AT THE SURFACE...HIGH PRESSURE IS LOCATED FAR
NORTH OF THE STATE...WITH A DISSIPATING FRONT JUST NORTHEAST OF THE
ISLANDS. THE 00Z SOUNDING FROM HILO SHOWS A MORE TYPICAL TRADE WIND
PROFILE...WITH A SUBSIDENCE INVERSION AROUND 6KFT AND PRECIPITABLE
WATER OF 1.4 INCHES. THE 00Z LIHUE SOUNDING ALSO SHOWS MORE DRYING
AND SUBSIDENCE...WITH A STRENGTHENING INVERSION AROUND 4-5KFT AND A
PW VALUE DOWN TO 1.7 INCHES. EARLY AFTERNOON MIMIC TOTAL
PRECIPITABLE WATER IMAGERY IS HIGHER THAN OBSERVED BY THE SOUNDINGS
AND GPS-MET SENSORS...BUT DOES SHOW THE QUALITATIVE DRYING TREND
FROM THE EAST. MIMIC ALSO SHOWS A BAND OF HIGHER MOISTURE ABOUT
100-150 MILES NORTHEAST OF THE STATE ASSOCIATED WITH THE WEAKENING
FRONT...WHICH WILL COME INTO PLAY OVER THE NEXT DAY OR TWO.

SO FAR THE COMBINATION OF STABILIZING AIRMASS...DECREASING
MOISTURE...AND THICK CLOUD COVER TO LIMIT INSOLATION HAS KEPT
CONVECTIVE ACTIVITY NEAR KAUAI TO A MINIMUM THROUGH THE DAY. RECENT
RADAR IMAGERY SHOWS SOME LIGHT TO MODERATE BANDS MOVING UP FROM THE
SOUTH...AND HAVE INCREASED RAINFALL CHANCES A BIG FOR KAUAI COUNTY.
HEAVY RAIN IS NOT ANTICIPATED...WITH MOST OF THESE RETURNS FROM THE
ELEVATED CLOUD DECK THAT HAS BEEN PERSISTENT OVER THE AREA.

ANA WILL CONTINUE MOVING WESTWARD...BUT WILL LEAVE THE MIDDLE AND
HIGH LEVEL LAYERED CLOUDS ACROSS PART OF THE STATE FOR THE NEXT
COUPLE DAYS. MODERATE TRADE WIND FLOW TONIGHT WILL WEAKEN SOMEWHAT
FROM TUESDAY INTO WEDNESDAY AS A PORTION OF A DISSIPATING FRONT
EMBEDDED IN THE TRADE FLOW MOVES ACROSS THE ISLANDS. THE 18Z GFS IS
MORE VIGOROUS WITH CONVECTION ALONG THIS OLD BOUNDARY...AND FORECAST
SOUNDINGS SHOW THE AIRMASS DESTABILIZING AGAIN. WITHOUT MUCH IN THE
WAY OF UPPER LEVEL SUPPORT THIS SEEMS OVERLY AGGRESSIVE...AND THE
SATURATED/UNSTABLE PROFILES MAY BE A RESULT OF CONVECTION IN THE
MODEL RATHER THAN AN INDICATOR OF IT. HOWEVER...THIS DOES BEAR
WATCHING AS SOME COLDER TOPS HAVE FLARED UP ALONG THE MOISTURE AXIS
THIS AFTERNOON. HAVE INCREASED RAINFALL CHANCES MAINLY FROM TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT ASSOCIATED WITH THIS FEATURE. IN
ADDITION...THE PERIODS OF LIGHTER WINDS WILL ALLOW LOCALIZED SEA
BREEZES TO FORM ACROSS SHELTERED LEEWARD AREAS...AND MAY CONTRIBUTE
ADDITIONAL CLOUDS AND SHOWERS ACROSS INTERIOR SECTIONS OF THE
ISLANDS DURING THE AFTERNOONS.

&&

.AVIATION...
ONLY THICK HIGH CLOUDS FROM THE CIRRUS BLOW OFF FROM ANA AFFECTING
THE STATE THIS AFTERNOON...MAINLY KAUAI. SMALLER AMOUNTS OF CIRRUS
OVER OAHU PERSIST AND MAY LINGER AND EVEN MOVE TO THE OTHER ISLANDS
TONIGHT. SOME UNCERTAINTY THERE. OTHERWISE...VFR CONDITIONS ARE
PREVAILING AGAIN STATEWIDE FROM OAHU TO THE BIG ISLAND NOW THROUGH
TUESDAY.

RECENTLY CANCELLED AIRMET FOR LOW LEVEL TURB OVER KAUAI AS DOPPLER
WIND PROFILE FROM KAUAI RADAR SHOWED WINDS HAD WEAKENED. TROPICAL
CYCLONE SIGMET QUEBEC SERIES FOR ANA.

&&

.MARINE...
THE WAIMEA BUOY ON OAHU CONTINUES TO REPORTS SEAS NEAR 8 FT. MOST
OF THIS ENERGY IS FROM A LARGE NORTH-NORTHWEST SWELL THAT HAS BEEN
AFFECTING THE ISLANDS. WAVEWATCH III GUIDANCE SHOWS THIS SWELL
DIMINISHING A BIT NOW BUT SURGING BACK BRIEFLY THIS EVENING. BASED
ON THESE VALUES...THE HIGH SURF ADVISORY IS IN EFFECT THROUGH THE
NIGHT. THE SWELL FROM TROPICAL STORM ANA CONTINUES TO DIMINISH. WITH
ANA WEAKENING AND MOVING WEST OF THE STATE...WE HAVE CANCELLED THE
HIGH SURF ADVISORY FOR SOUTH AND WEST FACING SHORES OF KAUAI COUNTY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST FOR NORTH FACING SHORES OF NIIHAU
KAUAI OAHU MOLOKAI MAUI AND THE BIG ISLAND.

&&

$$

DISCUSSION/MARINE...BRAVENDER
AVIATION...FUJII




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