Area Forecast Discussion
Issued by NWS Honolulu, HI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXHW60 PHFO 202123 AAA
AFDHFO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
1123 AM HST SAT DEC 20 2014

.UPDATE...
UPDATED HAZARD SECTION TO DROP THE WIND ADVISORY AND ADD HIGH SURF
WARNING.

&&

.SYNOPSIS...
WEAKENING SOUTHEASTERLY FLOW WILL ALLOW FOR LAND AND SEA BREEZES TO
DEVELOP THROUGH SUNDAY. A COLD FRONT APPROACHING FROM THE NORTHWEST
WILL BRING AN INCREASE IN SHOWERS AS EARLY AS SUNDAY NIGHT TO KAUAI.
THERE IS THE POTENTIAL FOR HEAVY RAIN AND A FEW THUNDERSTORMS ACROSS
THE STATE FROM MONDAY AFTERNOON THROUGH TUESDAY. STRONG NORTHERLY
WINDS WILL DEVELOP BEHIND THE FRONT.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL HIGH NORTHEAST OF THE
STATE...WITH A RIDGE EXTENDING ACROSS THE ISLANDS. A SHARP TROUGH IS
LOCATED FAR TO THE NORTHWEST...MOVING TO THE SOUTHEAST AT 30 MPH. AT
THE SURFACE...A RIDGE IS LOCATED LESS THAN 200 MILES NORTH OF
KAUAI...AND THE APPROACHING COLD FRONT IS ABOUT 700 MILES NORTHWEST
OF KAUAI. 12Z RAOBS SHOW STABLE INVERSIONS RANGING FROM 5KFT AT
LIHUE TO 7KFT AT HILO. PRECIPITABLE WATERS ARE ALSO 0.9-1.0
INCHES...WHICH IS DRIER THAN NORMAL FOR THIS TIME OF YEAR. EARLY
MORNING MIMIC TOTAL PRECIPITABLE IMAGERY SHOWS SIMILAR OR SLIGHTLY
DRIER AIR WITHIN A COUPLE HUNDRED MILES EAST OF THE STATE...WITH TPW
VALUES NEAR 1.5 INCHES POOLING ALONG THE COLD FRONT TO THE
NORTHWEST.

WITH THE SURFACE RIDGE BEING SUPPRESSED SOUTHWARD BY THE APPROACHING
FRONT...LOW-LEVEL WINDS HAVE ALREADY TURNED MORE SOUTHEASTERLY
ACROSS THE SMALLER ISLANDS. CLOUD MOTIONS SHOW EASTERLY WINDS STILL
AFFECTING THE BIG ISLAND. WINDS HAVE WEAKENED WITH THE RIDGE
NEARBY...AND WILL WEAKEN FURTHER AS THE WESTERN EXTENT OF THE RIDGE
ERODES WITH THE APPROACH OF THE COLD FRONT. SURFACE PRESSURES ACROSS
THE STATE HAVE ALREADY DROPPED ABOUT 2MB IN THE PAST 24 HOURS. WITH
THE SOUTHEASTERLY WIND DIRECTION...THE BIG ISLAND WILL ALSO BLOCK
SOME OF THE GRADIENT WIND FROM THE SMALLER ISLANDS...LEADING TO A
LOCALLY DRIVEN LAND AND SEA BREEZE PATTERN. THE STABLE AND DRY
AIRMASS WILL KEEP RAINFALL GENERALLY LIGHT...BUT WE WILL SEE AN
INCREASE IN CLOUDS AND SHOWERS ACROSS INTERIOR AND WEST/NORTHWEST
SECTIONS DURING THE LATE MORNING/AFTERNOON. THIS WILL BE THE CASE
BOTH TODAY AND ON SUNDAY...AS WINDS WILL REMAIN LIGHT OVER THE
ISLANDS.

WINDS ACROSS THE BIG ISLAND SUMMITS HAVE SHOWN A GRADUAL DOWNWARD
TREND THROUGH THE MORNING SO FAR. WHILE THE CFHT SENSOR HAS DROPPED
BELOW ADVISORY LEVELS FOR THE HIGHER ELEVATIONS...IT IS STILL
HOVERING AT UP TO 40 MPH. WE SHOULD BE ABLE TO DROP THE WIND
ADVISORY AS EXPECTED THIS MORNING.

THE UPPER LEVEL TROUGH NORTHWEST OF THE STATE WILL PROPEL THE COLD
FRONT TOWARD KAUAI BY SUNDAY NIGHT. MOST OF THE UPPER LEVEL SUPPORT
WITH THIS FIRST TROUGH WILL PASS TO OUR NORTH...AND THE FRONT IS
EXPECTED TO LOSE SOME OF ITS PUSH. HOWEVER...ANOTHER PIECE OF ENERGY
IS EXPECTED TO DIG DOWN THE BACK SIDE OF THE TROUGH AND AMPLIFY NEAR
THE ISLANDS...REINVIGORATING THE FRONT AND DRIVING IT FARTHER
SOUTHEAST. COLD AIR ASSOCIATED WITH THIS DIGGING TROUGH WILL ALSO
DESTABILIZE THE AIRMASS OVER THE ISLANDS. 500MB TEMPERATURES DROP TO
-12C TO -14C. MOISTURE WILL BE SOMEWHAT LIMITED...WITH CROSS
SECTIONS ACROSS THE ISLANDS SHOWING MOISTURE EXTENDING UP TO 700MB.
HOWEVER...MODEL FORECAST SOUNDINGS SHOW THE SUBSIDENCE INVERSION
ERODING...LEADING TO UNSTABLE PROFILES AND RELATIVELY SATURATED
LOW-LEVELS. DIFFERENCES REMAIN BETWEEN THE GFS AND ECMWF...WITH THE
GFS BEING MORE CONSISTENT THROUGH THE EXTENDED FORECAST. THE 12Z
ECMWF CUTS OFF MUCH OF THE DIGGING ENERGY SOUTHWEST OF THE STATE
WHILE THE GFS KEEPS THE TROUGH MORE PROGRESSIVE. BY MID WEEK THE
ECMWF TRENDS BACK TOWARD THE GFS SOLUTION WITH THE PLACEMENT OF A
CUTOFF LOW DEVELOPING NORTHEAST OF THE STATE. OVERALL THE PATTERN
HAS STABILIZED ENOUGH THAT CHANGES ARE NOT NEEDED FOR THE CURRENT
FORECAST...WHICH FEATURES A MENTION OF THUNDERSTORMS FROM MONDAY
AFTERNOON THROUGH TUESDAY NIGHT.

STRONG NORTHERLY WINDS ARE EXPECTED TO DEVELOP BEHIND THE FRONT
EARLY IN THE NEW WORK WEEK. THESE WINDS WILL GRADUALLY RELAX THROUGH
THE WEEK...BUT REMAIN GENERALLY OUT OF THE NORTH DUE TO THE PRESENCE
OF THE LOW THAT IS EXPECTED TO BE NORTHEAST OF THE STATE. BY LATE IN
THE WEEK THIS LOW WILL WEAKEN AND ALLOW HIGH PRESSURE TO BUILD
NORTHWEST OF THE STATE...WHICH WILL ALLOW WINDS TO VEER TO A MORE
NORTHEASTERLY DIRECTION.

&&

.AVIATION...
WEAK SOUTHEAST FLOW IS EXPECTED ACROSS THE WHOLE OF STATE TODAY AS
THE COLD FRONT TO OUR DISTANT NORTHWEST BEGINS ITS APPROACH. WEAK
EASTERLY TRADES THIS MORNING WILL BE REPLACED BY WEAK SEA BREEZES
THIS AFTERNOON AND WEAK LAND BREEZES LATE TONIGHT. MORNING
CLOUDINESS IS FOCUSED OVER WINDWARD SLOPES AND COASTS BUT AFTERNOON
AND EVENING CLOUDS WILL BECOME FOCUSED OVER ISLAND INTERIORS.
AIRMASS OVER THE ISLANDS TODAY IS RELATIVELY DRY AND THE SUBSIDENCE
INVERSION IS RELATIVELY LOW. ANY PRECIPITATION TODAY SHOULD BE LIGHT
AND VFR CONDS ARE EXPECTED TO PREVAIL THROUGH 24 HOURS. PARTIAL
CLEARING EXPECTED ALONG LEEWARD COASTS AFTER MIDNIGHT.

&&

.MARINE...
A LONG PERIOD NORTHWEST SWELL GENERATED BY A LARGE AND POWERFUL LOW
PRESSURE SYSTEM IS EXPECTED TO BRING WARNING LEVEL SURF TO THE
ISLANDS ON SUNDAY. A JASON ALTIMETER PASS FROM LAST NIGHT JUST
OUTSIDE THE CORE OF THE HIGHEST SEAS SUPPORTS THE CURRENT WAVEWATCH
III FORECAST. WW3 SHOWS A SWELL OF 12-13 FEET REACHING BUOY 51101
AFTER MIDNIGHT TONIGHT. THIS SWELL WILL BUILD ACROSS THE ISLANDS ON
SUNDAY...THEN LINGER INTO MONDAY BEFORE GRADUALLY DIMINISHING. HAVE
ISSUED A HIGH SURF WARNING FOR NORTH AND WEST FACING SHORES OF THE
SMALLER ISLANDS. GIVEN THE LATER TIMING FOR THE BIG ISLAND /SWELL
ARRIVING SUNDAY NIGHT/ HAVE HELD OFF ON INCLUDING THE WEST SIDE.
HOWEVER...WAVEWATCH GUIDANCE OF 6 FEET/17 SECONDS OFF THE KONA
COAST WILL ALSO LEAD TO WARNING LEVEL SURF THERE AS WELL. THE SWELL
THIS LARGE WILL ALSO LEAD TO SMALL CRAFT CONDITIONS ACROSS THE
COASTAL WATERS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING FROM 4 AM SUNDAY TO 6 AM HST TUESDAY FOR NORTH AND
WEST FACING SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI AND FOR NORTH
FACING SHORES OF MAUI.

&&

$$

DISCUSSION/MARINE...BRAVENDER
AVIATION...BEDAL





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.