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Hawaiian Islands Synoptic Discussion and Guidance

844
FXHW60 PHFO 202029
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST MON OCT 20 2014

.SYNOPSIS...
WIDESPREAD RAIN HAS TAPERED OFF AS TROPICAL STORM ANA MOVES FARTHER
AWAY FROM THE STATE. MODERATE EAST-SOUTHEAST WINDS WILL FOCUS
SHOWERS ACROSS EASTERN SECTIONS OF THE ISLANDS TODAY...THEN BECOME
LIGHTER FROM TUESDAY THROUGH THE END OF THE WEEK. AFTER A DRIER
PERIOD FOR THE NEXT COUPLE DAYS...WE COULD SEE AN INCREASE IN
SHOWERS BY THE MIDDLE OF THE WEEK.

&&

.DISCUSSION...
AT 8 AM HST...TROPICAL STORM ANA WAS LOCATED 250 MILES
WEST-SOUTHWEST OF LIHUE...AND IS MOVING TO THE WEST AT 10 MPH.
CURRENT RADAR IMAGERY SHOWS HEAVY RAIN HAS MOVED WEST OF THE COASTAL
WATERS...WITH STEADY LIGHT TO MODERATE SHOWERS WEST OF 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 DAY.

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 12Z SOUNDING FROM HILO SHOWS A MORE TYPICAL TRADE WIND
PROFILE...WITH A SUBSIDENCE INVERSION AROUND 6KFT AND PRECIPITABLE
WATER OF 1.4 INCHES. THE 12Z LIHUE SOUNDING SHOWS A DEVELOPING
INVERSION WITH SOME WARMING/DRYING FROM 900-700MB...BUT OVERALL IT
REMAINS UNSTABLE. THE PRECIPITABLE WATER AT LIHUE WAS 2.1 INCHES.
EARLY MORNING MIMIC TOTAL PRECIPITABLE WATER IMAGERY SHOWS THIS
DRYING FROM THE EAST...AND THE GPS-MET SENSOR ON HONOLULU SHOWS A
DECREASE IN PW LAST NIGHT. MIMIC ALSO SHOWS A BAND OF HIGHER
MOISTURE ABOUT 200 MILES NORTHEAST OF THE STATE ASSOCIATED WITH THE
FRONT...WHICH WILL COME INTO PLAY OVER THE NEXT DAY OR TWO.

EVEN THOUGH THE 12Z LIHUE SOUNDING WAS VERY MOIST AND UNSTABLE...A
19Z ACARS FLIGHT INTO LIHUE SHOWED MORE WARMING AROUND 5KFT...A SIGN
OF THE INVERSION FURTHER STRENGTHENING. EVEN WITH THE MOIST
AIRMASS...THE COMBINATION OF DRYING AND STABILIZING LOW LEVELS AND A
VERY THICK LAYER OF MIDDLE AND HIGH CLOUDS TO LIMIT INSOLATION WILL
LIMIT POTENTIAL FOR THUNDERSTORMS OR HEAVY RAIN. THEREFORE WE DO NOT
ANTICIPATE FLOODING CONDITIONS TODAY...AND HAVE DROPPED THE FLASH
FLOOD WATCH THAT WAS IN EFFECT FROM OAHU WESTWARD. UPDATED THE
FORECAST BASED ON LATEST DRYING TRENDS TO LOWER RAINFALL CHANCES
ACROSS MOST AREAS.

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. GENERAL MODERATE EASTERLY FLOW WILL ALSO WEAKEN
SOMEWHAT TUESDAY NIGHT/WEDNESDAY AS A PORTION OF A DISSIPATING FRONT
EMBEDDED IN THE TRADE FLOW MOVES ACROSS THE ISLANDS. THIS WILL BRING
AN INCREASE IN WINDWARD SHOWERS MAINLY TUESDAY NIGHT THROUGH
WEDNESDAY NIGHT. WINDS WILL BE LIGHT ENOUGH TO ALLOW SEA BREEZES TO
FORM ACROSS SHELTERED LEEWARD AREAS...AND MAY CONTRIBUTE SOME
CLOUDS AND SHOWERS ACROSS INTERIOR SECTIONS OF THE ISLANDS DURING
THE AFTERNOON.

&&

.AVIATION...
AS ANA CONTINUES TO WEAKEN AND MOVE FURTHER AWAY FROM THE STATE...
VFR CONDITIONS TO PREVAIL AGAIN FROM OAHU TO THE BIG ISLAND TODAY
INTO TUESDAY. KAUAI SEEING MOSTLY MID AND HIGH LEVEL CLOUDINESS BUT
SHOULD CONTINUE TO TEMPO MVFR CEILINGS AND VISIBILITIES AT EAST
THROUGH THIS AFTERNOON. RADAR SHOWING FEWER SHOWERS OVER THE GARDEN
ISLE AS WE SPEAK BUT STILL FORMING MAINLY OVER THE SOUTHWEST HALF OF
THE ISLAND.

DOPPLER WIND PROFILE FROM KAUAI RADAR SHOWS WINDS SLACKENING OFF IN
THE LOWER LEVELS THUS THE CURRENT AIRMET FOR LOW LEVEL TURB
CURRENTLY FOR THAT ISLAND MAY BE DISCONTINUED LATER TODAY. TROPICAL
CYCLONE SIGMET QUEBEC SERIES CONTINUES FOR NOW UNTIL ANA WEAKENS
BELOW TROPICAL STORM STATUS.

&&

.MARINE...
THE HANALEI BUOY ON KAUAI IS STILL RUNNING NEAR 10FT AND THE WAIMEA
BUOY ON OAHU IS NEAR 8 FT. ONE CONTRIBUTOR TO THESE SEAS IS A LARGE
NORTH SWELL. WAVEWATCH III GUIDANCE SHOWS THIS SWELL DIMINISHING A
BIT TODAY BUT SURGING BACK HIGHER THIS EVENING. BASED ON THESE
VALUES...WE HAVE EXTENDED THE HIGH SURF FOR NORTH FACING SHORES
THROUGH TONIGHT. CONDITIONS SHOULD BE FALLING OVERNIGHT. A SECOND
CONTRIBUTOR TO THE HIGH SEAS IS THE SWELL FROM TROPICAL STORM ANA.
AS ANA CONTINUES MOVING WEST...THIS SWELL WILL HAVE LESS OF AN
IMPACT. HOWEVER...WE KEPT THE HIGH SURF IN EFFECT FOR SOUTH AND WEST
FACING SHORES OF KAUAI AND NIIHAU FOR NOW. BASED ON THE HIGH VALUES
OBSERVED AT HANALEI...WE ALSO EXTENDED THE SMALL CRAFT ADVISORY FOR
WATERS AROUND KAUAI THROUGH THE DAY DUE TO HAZARDOUS SEAS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST TUESDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-OAHU NORTH
SHORE-OAHU KOOLAU-MOLOKAI-MAUI WINDWARD WEST-WINDWARD HALEAKALA-
BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL.

&&

$$

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



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