Monday, September 22, 2014 596-SURF , 596-WAVE , 922-BONG , 638-RUSH , 572-SURF(MAUI) , 241-SURF (KAUAI) , 324-RUSH (BIG ISLAND)
   
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000
FXHW60 PHFO 220153
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST SUN SEP 21 2014

.SYNOPSIS...
SPOTTY HEAVY SHOWERS DRIVEN BY A HUMID SEA BREEZE REGIME WILL
DIMINISH RAPIDLY ON THE SMALLER ISLANDS LATE THIS AFTERNOON BUT
WILL LINGER INTO EARLY EVENING ON LEEWARD BIG ISLAND. SOME RELIEF
FROM THE HUMIDITY IS ON THE WAY...AS TRADES WILL GRADUALLY
STRENGTHEN MONDAY AND TUESDAY. SHOWERS BECOME FOCUSED ACROSS
WINDWARD SLOPES...THOUGH CLOUDS AND A FEW SHOWERS WILL CONTINUE TO
DEVELOP OVER LEEWARD TERRAIN EACH AFTERNOON. A WETTER TRADE WIND
PATTERN IS EXPECTED DURING THE SECOND HALF OF THE WEEK.

&&

.DISCUSSION...
THIS AFTERNOON FEATURES A CONTINUED AND UNCOMFORTABLE HUMID SEA
BREEZE REGIME. AFTERNOON TEMPERATURES ARE RUNNING IN THE HIGH 80/S
TO AROUND 90...BUT WITH DEW POINTS RUNNING IN THE LOW TO MID
70/S...THE TEMPERATURE FEELS MORE LIKE THE MID 90/S. LOOK FOR ONE
MORE WARM AND HUMID NIGHT.

THE SEA BREEZES ARE TRIGGERING SPOTTY HEAVY SHOWERS ON THE ISLANDS
THIS AFTERNOON ALONG WITH SOME THUNDERSTORMS ON THE BIG ISLAND.
ENHANCED LOW LEVEL MOISTURE ALONG THE FLANK OF A WEAK SURFACE
TROUGH PASSING SEVERAL HUNDRED MILES SOUTHWEST OF THE SATE IS
HELPING TO FUEL THE CONVECTION. THIS MOISTURE IS FOCUSED MORE THE
BIG ISLAND...WHERE SHOWERS ARE MORE ACTIVE...AND AN OVERLYING UPPER
LEVEL TROUGH IS TRIGGERING THUNDERSTORMS...MAINLY IN THE KAU
DISTRICT. CENTRAL OAHU IS ALSO EXPERIENCING SPOTTY HEAVY SHOWERS
DUE TO SEA BREEZE CONVERGENCE FROM THE NORTH AND SOUTH SHORES.
SHOWER ACTIVITY WILL TAPER OFF ON THE SMALLER ISLANDS LATE THIS
AFTERNOON BUT WILL LIKELY LINGER INTO EARLY EVENING ACROSS LEEWARD
BIG ISLAND.

THE BACKGROUND TRADE WIND FLOW WILL REMAIN WEAK TONIGHT...LEADING TO
ONE LAST NIGHT OF WIDESPREAD LAND BREEZES. A NEARLY STATIONARY
REMNANT FRONT 400 MILES NORTH OF KAUAI AND A WEAK SURFACE TROUGH
ABOUT 275 MILES NORTH OF MAUI WILL WEAKEN OVERNIGHT AS HIGH PRESSURE
BUILDS TO THE NORTHWEST...BUT THE TRADES SHOULD REMAIN LIGHT ENOUGH
FOR DOMINANT LAND BREEZES...ESPECIALLY LEEWARD. SOME CLOUDS AND A
FEW EVENING SHOWERS ARE POSSIBLE OVER LEEWARD AREAS...ESPECIALLY ON
THE BIG ISLAND...BUT EXPECT CLEARING SKIES AS THE ENHANCED MOISTURE
MOVES OFF TO THE WEST. WINDWARD SLOPES COULD SEE A FEW SHOWERS ON
THE BUILDING TRADE WIND FLOW...BUT ASIDE FROM WINDWARD BIG ISLAND...
NOT MUCH RAINFALL IS EXPECTED.

TRADE WINDS WILL BUILD ON MONDAY AND TUESDAY...BRINGING SOME RELIEF.
LOW LEVEL MOISTURE WILL INITIALLY DECREASE AS SLIGHTLY DRIER AIR
MOVES IN BEHIND THE DEPARTING SURFACE TROUGH TO THE SOUTHWEST. EVEN
THOUGH THE DEW POINT TEMPS WILL ONLY BE DROPPING A COUPLE OF
DEGREES...THE COMBINATION SLIGHTLY DRIER CONDITIONS AND BUILDING
GENTLE TRADE WINDS WILL BE NOTICEABLE. LEEWARD AREAS WILL REMAIN
HOT...WITH SHELTERED AREAS NEAR TERRAIN EXPERIENCING SOME AFTERNOON
CLOUDS AND A SLIGHT CHANCE OF SHOWERS ON MONDAY. TRADES WILL
STRENGTHEN TO MODERATE LEVELS ON TUESDAY...AND A TYPICAL...
WINDWARD-FOCUSED SHOWER REGIME WILL PREVAIL.

A WET TRADE WIND RAINFALL PATTERN IS DUE DURING THE SECOND PART OF
THE WEEK. FORECAST MODELS ARE SHOWING A BAND OF REMNANT FRONTAL
MOISTURE SAGGING SOUTHWARD OVER THE SMALLER ISLANDS WEDNESDAY AND
STALLING THURSDAY. INITIAL INDICATIONS ARE THAT THIS BAND COULD
STICK AROUND INTO NEXT WEEKEND...KEEPING MAINLY WINDWARD AREAS WET.
FOR NOW...THE FORECAST BROAD BRUSHES WET CONDITIONS...BUT LOOK FOR
FINE TUNING AS WE GET A HANDLE ON WHICH ISLANDS WILL BE MOST
AFFECTED BY THE MOISTURE BAND.

&&

.AVIATION...
CONVECTION HAS FLARED UP OVER INTERIOR AND LEEWARD OAHU AND THE BIG
ISLAND THIS AFTERNOON. TCU TOPS ON OAHU ARE REACHING AROUND 23 KFT.
ON THE BIG ISLAND...THUNDERSTORMS HAVE FORMED OVER THE SOUTHERN
HALF...INCLUDING KAU AND SOUTH KONA DISTRICTS...WITH CB TOPS BETWEEN
30 AND 35 KFT AND SOME REACHING ABOVE 40 KFT. EXPECT MVFR WITH
PERIODS OF IFR CIGS/VIS TO BE EMBEDDED WITHIN THESE SHOWERS.
HOWEVER...MAIN ISLAND TERMINALS HAVE REMAINED PREDOMINATELY VFR AND
SHOULD CONTINUE TO DO SO.

ON ALL ISLANDS...CONVECTIVE ACTIVITY SHOULD BEGIN TO DIMINISH WITH
SUNSET. OVERNIGHT...ONLY BRIEF MVFR CONDITIONS IN PASSING SHOWERS
WILL REMAIN...MAINLY FOR WINDWARD AND MAUKA AREAS. TRADE WINDS ARE
EXPECTED TO GRADUALLY RETURN TOMORROW...AND SHOWER ACTIVITY WILL
MAINLY FOCUS ALONG WINDWARD AND MAUKA AREAS WITH A FEW CLOUDS
DEVELOPING OVER LEEWARD AREAS.

&&

.MARINE...
NO ISSUES IN THE SHORT TERM. INCREASING TRADE WINDS WILL BRING
BORDER LINE SMALL CRAFT ADVISORY WINDS TO THE TYPICALLY WINDY WATERS
AROUND THE BIG ISLAND AND MAUI COUNTY STARTING TUESDAY. SURF WILL
REMAIN AROUND BACKGROUND LEVELS THROUGH MUCH OF THE WEEK. A
SLIGHTLY HIGHER SWELL OF AROUND 4 FEET IS EXPECTED FROM THE NNE
THURSDAY THROUGH SATURDAY. A MODERATE SSW IS DUE NEXT WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION/MARINE...WROE
AVIATION...EATON


The Weather Prediction Center

College Park, MD

Hawaii Extended Forecast Discussion




Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
829 AM EDT Sun Sep 21 2014

Valid 00Z Mon Sep 22 2014 - 00Z Mon Sep 29 2014

Latest models and ensembles still show reasonable agreement on
upper ridging initially NW of Hawaii near the Dateline to move
gradually eastward along 30N through much of next week. Elevated
precipitable water values over the Big Island this weekend will
drop off below climatological values (which are just under 1.50
inches) to about 1.20 inches through midweek. After about midweek,
the upper/surface high near 165W and approach of a front from the
north and into the islands should increase moisture pooling and
enhanced shower potential over the state that should linger into
next weekend. With associated development of a stronger than
average pressure gradient, trades should be higher than average.

Schichtel





Last Updated: 829 AM EDT Sun Sep 21 2014




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