Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 220626
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST MON JUL 21 2014

.SYNOPSIS...
MOIST AND UNSTABLE CONDITIONS WILL CONTINUE THROUGH TONIGHT. SPOTTY
HEAVY SHOWERS AND THUNDERSTORMS ARE POSSIBLE NEAR AND AROUND OAHU
AND KAUAI. DRIER AND INCREASINGLY STABLE TRADE WIND WEATHER WILL
BUILD OVER THE ISLANDS LATER TUESDAY AND WEDNESDAY.

&&

.DISCUSSION...
OUR AIRMASS REMAINS MOIST AND UNSTABLE THIS EVENING...BUT THE FOCUS
FOR THUNDERSTORMS CURRENTLY LIES SEVERAL HUNDRED MILES NORTH AND
NORTHWEST OF THE MAIN HAWAIIAN ISLANDS. AN UPPER LOW NEAR
30N166W...FAR NORTHWEST OF THE MAIN ISLANDS...IS GRADUALLY WEAKENING
BUT CONTINUES TO INDUCE TROUGHING AT THE SURFACE NORTHWEST OF KAUAI
AND NORTH THROUGH EAST OF MAUI. RADAR AND SATELLITE DATA SHOW
THUNDERSTORMS NEAREST THE ISLANDS ARE FORMING ALONG THESE TROUGHS
NORTH OF 33N...REDUCING LOW LEVEL MOISTURE NEEDED TO FUEL
WIDESPREAD HEAVY SHOWERS AND THUNDERSTORMS OVER THE IMMEDIATE AREA.

THE SURFACE TROUGH NORTH THROUGH EAST OF MAUI WILL PASS OVER AND
JUST NORTH OF THE ISLANDS TONIGHT WITHIN EASTERLY TRADE WIND FLOW.
AS THE MOISTURE ASSOCIATED WITH THIS TROUGH COMES IN...WE EXPECT AN
INCREASE IN WINDWARD SHOWERS. THE UPPER LEVEL LOW WILL CONTINUE TO
WEAKEN...BUT MODELS SHOW A SHORTWAVE UPPER TROUGH MAY PASS OVER THE
WESTERN END OF THE ISLAND CHAIN. THEREFORE HEAVY SHOWERS AND
POSSIBLE THUNDERSTORMS REMAIN THE FORECAST FOR KAUAI AND OAHU
THROUGH TONIGHT. ALSO...THE FLASH FLOOD WATCH REMAINS IN EFFECT
THROUGH TONIGHT FOR ONLY THESE ISLANDS.

WHILE THE THREAT FOR HEAVY RAINFALL WILL DIMINISH ON TUESDAY...OUR
MOIST AND HUMID AIR MASS WILL KEEP SHOWER CHANCES RELATIVELY HIGH.
SHOWERS WILL FAVOR WINDWARD SLOPES...BUT LEEWARD POPS WILL REMAIN
SOMEWHAT HIGH AS WELL GIVEN THE AMOUNT OF AVAILABLE MOISTURE TO FUEL
RAINFALL. EVEN THOUGH TRADE WINDS WILL BE A BIT STRONGER THAN
TODAY...HUMID CONDITIONS WILL PREVAIL THROUGH MUCH OF THE DAY AS DEW
POINTS HOVER IN THE LOW TO MID 70/S.

DRIER AND INCREASINGLY STABLE TRADE WIND WEATHER WILL BUILD OVER THE
STATE LATE TUESDAY AND WEDNESDAY. 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. THIS WILL FOCUS CLOUDS AND MODEST SHOWERS OVER WINDWARD
SLOPES. LEEWARD AREAS WILL BE RATHER DRY...WITH THE EXCEPTION OF
LEEWARD BIG ISLAND SLOPES WHERE AFTERNOON CLOUDS AND SHOWERS WILL
DEVELOP. TRADE WINDS SHOULD DECREASE A BIT TOWARDS THE WEEKEND AS
THE HIGH TO OUR NORTH WEAKENS SLIGHTLY.

&&

.MARINE...
EXPECT TRADE WINDS TO INCREASE TONIGHT INTO WEDNESDAY. A SMALL CRAFT
ADVISORY /SCA/ HAS BEEN ISSUED AHEAD OF THE INCREASE FOR THE
TYPICALLY WINDY LOCATIONS AROUND THE BIG ISLAND AND MAUI. THE SCA
THEN EXPANDS TO INCLUDE THE KAIWI CHANNEL ON TUESDAY. TRADES SHOULD
DROP A NOTCH ON FRIDAY WITH BORDER LINE SCA CONDITIONS DUE IN THE
TYPICALLY WINDY AREAS 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...
WE WILL MONITOR CLOSELY THE NECESSITY FOR AIRMET SIERRA FOR
MOUNTAIN OBSCURATION FOR N THROUGH E FACING MTN ON ALL ISLANDS.
THERE IS AN OUTSIDE CHANCE IT WILL BE LOWERED. BUT FOR NOW...IT WILL
LIKELY BE RENEWED AT 1000Z. SPOTTY SHOWERS WILL OCCASIONALLY REDUCE
CIG AND VIS TO MVFR LIMITS. OTHERWISE...VFR RULES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH 6 AM HST TUESDAY FOR OAHU...KAUAI... AND
NIIHAU.

SMALL CRAFT ADVISORY THROUGH 6 PM HST THURSDAY FOR PAILOLO AND
ALENUIHAHA CHANNELS AND BIG ISLAND LEEWARD WATERS.

SMALL CRAFT ADVISORY FROM 6 AM HST TO 6 PM HST THURSDAY FOR KAIWI
CHANNEL...MAALAEA BAY AND BIG ISLAND SOUTHEAST WATERS.

&&

$$

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






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