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Hawaiian Islands Synoptic Discussion and Guidance

744
FXHW60 PHFO 221330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST TUE JUL 22 2014

.SYNOPSIS...
DRIER AND INCREASINGLY STABLE TRADE WIND WEATHER WILL BUILD OVER THE
ISLANDS TODAY AND WEDNESDAY. LOW CLOUDS AND SHOWERS WILL FAVOR
WINDWARD AND MAUKA AREAS. THICK HIGH CLOUDS WILL BEGIN TO CLEAR OUT
WEDNESDAY.

&&

.DISCUSSION...
SURFACE TROUGHING TO THE WEST OF KAUAI KEEPS LOW LEVEL WINDS FROM
THE EAST SOUTHEAST ACROSS LOCAL WATERS THIS MORNING. HOWEVER...
PRESSURE RISES SHOW THAT TRADE WINDS ARE TRYING TO BUILD WESTWARD
ACROSS THE AREA. RADAR SHOWS THAT SHOWERS DECREASED DRAMATICALLY
ACROSS MOST ISLANDS OVERNIGHT...WHILE LIGHT TO MODERATE ISOLATED
SHOWERS PERSISTED OVER EAST AND SOUTHEAST PORTIONS OF MAUI...LANAI
AND MOLOKAI. ADDITIONAL SHOWERS ARE FORMING IN THE KAIWI CHANNEL
JUST EAST OF OAHU. HIGH CLOUDS MARKING THE SOUTHEASTERN FLANK OF AN
UPPER LOW FAR NORTHWEST OF THE MAIN ISLAND CHAIN CONTINUE TO STREAM
NORTHEASTWARD ACROSS ALL ISLANDS EXCEPT KAUAI AND NIIHAU. THE
CLOSEST THUNDERSTORMS ASSOCIATED WITH THE UPPER LOW ARE ABOUT 200
MILES NORTHEAST OF OAHU.

THE UPPER LOW IS WEAKENING AND THE THREAT OF HEAVY RAINFALL...
THUNDERSTORMS...AND FLASH FLOODING HAS DECREASED ENOUGH TO DROP THE
FLASH FLOOD WATCH FOR KAUAI AND OAHU. MODELS SHOW SURFACE WINDS WILL
GRADUALLY SWING BACK TO EAST NORTHEAST TRADES OVER THE NEXT 24
HOURS. LOW CLOUDS AND SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS AS
WE TRANSITION BACK TO A TRADE WIND WEATHER PATTERN TODAY THROUGH
WEDNESDAY. LEEWARD AREAS WILL BE RATHER DRY...WITH THE EXCEPTION OF
LEEWARD BIG ISLAND SLOPES WHERE AFTERNOON CLOUDS AND SHOWERS WILL
DEVELOP. MID TO UPPER LEVEL RIDGING WILL GRADUALLY BUILD...CREATING
A TYPICAL SUMMER TIME INVERSION AROUND 6000 TO 8000 FT THAT WILL
STABILIZE THE ATMOSPHERE. TRADE WINDS WILL INCREASE AS A 1032 MB
HIGH REMAINS PARKED ABOUT 1400 MILES NORTH OF THE STATE. TRADE WINDS
SHOULD DECREASE A BIT TOWARDS THE WEEKEND AS THIS HIGH WEAKENS
SLIGHTLY.

&&

.MARINE...
EXPECT TRADE WINDS TO INCREASE TODAY INTO WEDNESDAY. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR THE TYPICALLY WINDY WATERS AROUND MAUI AND
THE BIG ISLAND AS WELL AS FOR THE KAIWI CHANNEL. TRADES SHOULD DROP
A NOTCH ON FRIDAY...WITH BORDERLINE SMALL CRAFT ADVISORY CONDITIONS
EXPECTED IN THE TYPICALLY WINDY WATERS FOR THE WEEKEND.

NO SIGNIFICANT SWELLS ARE SEEN FOR THE UPCOMING WEEK. THE BIGGEST
SURF WILL FROM TRADE WIND SWELL ALONG EAST FACING SHORES.

&&

.AVIATION...
BASED ON THE LATEST SFC OBS...AIRMET SIERRA FOR THE WINDWARD AND MTN
AREAS OF OAHU...LANAI AND THE BIG ISLAND...WILL BE LOWERED STARTING
WITH THE 1600Z PACKAGE. A RETURNING TRADE WIND FLOW WITH A MORE
STABLE AIR MASS HAS REACHED MAUI AND WILL CONTINUE TO SPREAD
WESTWARD...SLATED TO REACH KAUAI LATE THIS MORNING. WITH THIS SAID...
EXPECT SHOWERS TO START AFFECTING THE WINDWARD AND MOUNTAIN AREAS OF
THE LARGER ISLANDS. IT IS UNCERTAIN HOW MOIST THIS TRADE WIND REGIME
IS...SO IT WILL BE MONITORED CLOSELY IF IT MAY WARRANT AN AIRMET
SIERRA. IF SO...AIRMET SIERRA WILL PERTAIN TO THE WINDWARD AND MTN
AREAS.

FOR THE NEXT COUPLE OF HOURS UP TO MID MORNING...THE AIR MASS IS
SUPPORTIVE OF A FEW BRIEF SHOWERS FOR ANY POINTS ON MOLOKAI...OAHU
AND KAUAI. THIS IS IN LIGHT OF THE PRESENCE OF MVFR CEILINGS AT 15
HUNDRED FEET AT THEIR RESPECTIVE TERMINALS.

CONVECTIVE SHOWER ACTIVITY FOR THE KONA SLOPES THIS AFTERNOON IS
EXPECTED TO BE ISOLATED AT BEST WITH BRIEF MVFR CONDS.

OTHERWISE...VFR IS THE ANTICIPATED FOR FLYING CONDITIONS FOR TODAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY THROUGH 6 PM HST THURSDAY FOR KAIWI...PAILOLO
AND ALENUIHAHA CHANNELS...MAALAEA BAY AND WATERS SOUTH OF THE BIG
ISLAND.

&&

$$

PUBLIC AND MARINE...POWELL
AVIATION...LAU






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