Winter Weather Advisory 21, NWS Honolulu, HI

158 
WWHW40 PHFO 222137
WSWHFO

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE HONOLULU HI
1137 AM HST THU DEC 22 2011

HIZ028-222245-
/O.CAN.PHFO.WW.Y.0021.000000T0000Z-111222T2200Z/
BIG ISLAND SUMMITS-
INCLUDING THE CITY OF...MAUNA LOA AND MAUNA KEA ABOVE 8000 FEET
1137 AM HST THU DEC 22 2011

...WINTER WEATHER ADVISORY IS CANCELLED...

THE NATIONAL WEATHER SERVICE IN HONOLULU HAS CANCELLED THE WINTER
WEATHER ADVISORY. 

THE UPPER LEVEL SYSTEM THAT BROUGHT THE CHANCE FOR WINTRY WEATHER
HAS DRIFTED SOUTHWARD...REDUCING THE CHANCE FOR ANY FURTHER
ACCUMULATIONS. THUS THE WINTER WEATHER ADVISORY HAS BEEN CANCELLED.

$$

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED DEC 21 2011

.SYNOPSIS...
AN UPPER-LEVEL LOW SOUTH OF THE STATE WILL COMBINE WITH GUSTY TRADES
AND ABUNDANT MOISTURE TO PRODUCE PERIODS OF ENHANCED WINDWARD
RAINFALL THROUGH THE HOLIDAY WEEKEND. SOME OF THESE SHOWERS WILL
ALSO BE TRANSPORTED TO LEEWARD AREAS OF THE SMALLER HAWAIIAN ISLANDS
BY THE BLUSTERY TRADES. LOCALLY HEAVY SHOWERS REMAIN POSSIBLE IN THE
VICINITY OF THE BIG ISLAND THROUGH THURSDAY NIGHT. A MORE TYPICAL
TRADE WIND WEATHER PATTERN WILL GRADUALLY RETURN TO THE ALOHA STATE
EARLY NEXT WEEK.

&&

.DISCUSSION...
AN EAST NORTHEAST TO WEST SOUTHWEST ORIENTED SUBTROPICAL RIDGE IS
LOCATED ABOUT 560 MILES NORTH OF HONOLULU. THE TIGHT PRESSURE
GRADIENT BETWEEN THIS FEATURE AND A NORTH NORTHEAST TO SOUTH
SOUTHWEST ORIENTED SURFACE TROUGH JUST SOUTH OF THE STATE CONTINUES
TO MAINTAIN A ROBUST LOW-LEVEL TRADE WIND FLOW ACROSS THE AREA EARLY
THIS EVENING.

ALOFT...MID- TO UPPER-LEVEL LOW PRESSURE REMAINS ABOUT 500 MILES
SOUTH SOUTHWEST OF HILO ACCORDING TO LOOPS OF WATER VAPOR IMAGERY
AND SATELLITE DERIVED UPPER LEVEL WINDS. AN UPPER TROPOSPHERIC
TROUGH ALSO EXTENDS NORTHWARD FROM THE LOW PRESSURE ALOFT TO THE
VICINITY OF THE BIG ISLAND. AS A RESULT...ATMOSPHERIC CONDITIONS
REMAIN RELATIVELY UNSTABLE OVER THE EASTERN END OF THE STATE...WHERE
NO REAL INVERSION IS EVIDENT IN THE HILO SOUNDING FROM 200 PM HST
THIS AFTERNOON. THIS IS IN STARK CONTRAST WITH AN INVERSION LOCATED
JUST BELOW 6 THOUSAND FEET IN THE LIHUE SOUNDING AT THE SAME TIME.
THEREFORE...THE ATMOSPHERE CONTINUES TO GRADUALLY STABILIZE OVER THE
WESTERN ISLANDS. ALSO OF SIGNIFICANCE IS THE PRECIPITABLE WATER
VALUES AT HILO...WHICH WAS 1.45 INCHES COMPARED WITH ONLY 0.86 AT
LIHUE.

THE INCREASING STABILITY AND DECREASING MOISTURE MOVING FROM EAST TO
WEST UP THE ISLAND CHAIN IS EVIDENT IN THE COVERAGE OF LOW CLOUDS
AND TRADE SHOWERS AS SHOWN ON SATELLITE AND RADAR IMAGERY EARLY THIS
EVENING. THE GREATEST CONCENTRATION OF CLOUDS AND SHOWERS REMAINS
OVER THE EASTERN ISLANDS...WHERE LOCALLY HEAVY SHOWERS ARE IN THE
FORECAST OVER THE WINDWARD BIG ISLAND THROUGH THURSDAY NIGHT.
ELSEWHERE...RAINFALL WILL REMAIN FOCUSED MAINLY ALONG WINDWARD
FACING SLOPES AND TERRAIN. THE FRESH TO LOCALLY STRONG TRADES WILL
CONTINUE TO TRANSPORT SOME OF THESE SHOWERS OVER TO LEEWARD SECTIONS
OF THE SMALLER HAWAIIAN ISLANDS. SOME FROZEN PRECIPITATION IS ALSO
POSSIBLE ABOVE 12 THOUSAND FEET ON THE BIG ISLAND SUMMITS...WITH
SOME SLIGHT ACCUMULATION EXPECTED DURING THE NEXT 24 TO 36 HOURS.

THE WIND ADVISORY FOR THE SUMMIT OF MOUNT HALEAKALA ON MAUI
CONTINUES THROUGH THURSDAY AFTERNOON. WINDS HAD DROPPED JUST BELOW
WIND ADVISORY CRITERIA EARLIER THIS AFTERNOON. HOWEVER...THE LATEST
OBSERVATIONS AND FORECAST MODEL GUIDANCE CONTINUES TO SUGGEST THE
SUSTAINED WINDS WILL REMAIN NEAR THE 30 MPH THRESHOLD FOR THE
FORESEEABLE FUTURE.

THE LATEST FORECAST MODEL OUTPUT INDICATES UPPER-LEVEL TROUGHING
WILL REMAIN IN THE VICINITY OF THE MAIN HAWAIIAN ISLANDS THROUGH
MOST OF THE HOLIDAY WEEKEND. THE DYNAMIC LIFT DUE TO THIS
UPPER-LEVEL CYCLONIC FLOW AND THE ASSOCIATED COOLER TEMPERATURES
ALOFT WILL LIKELY KEEP ENOUGH INSTABILITY IN PLACE TO ALLOW THE
DEVELOPMENT OF BRIEF WINDWARD DOWNPOURS THROUGH THIS WEEKEND.

AT THE SAME TIME...THE TIGHT PRESSURE GRADIENT SOUTH OF SUBTROPICAL
RIDGING TO THE NORTH OF THE ALOHA STATE WILL MAINTAIN GENERALLY
FRESH TRADES. SO...LEEWARD AREAS OF THE SMALLER ISLANDS WILL ALSO
LIKELY EXPERIENCE PASSING SHOWERS THIS WEEKEND. TYPICAL HAWAIIAN
TRADE WEATHER MAY NOT RETURN AGAIN UNTIL SOME TIME EARLY NEXT WEEK.

&&

.AVIATION...
BASED ON EARLIER REPORTS FROM SEVERAL CESSNA AIRCRAFT...SIGMET OSCAR
WAS ISSUED FOR MOD TO OCNL SEV CAT FROM THE THE SFC TO 8 KFT OVER
AND IMT S THRU W OF ALL ISLANDS. IF THIS SIGMET IS CANCELLED LATER
TONIGHT...IT WILL BE FOLLOWED BY AN AIRMET FOR TEMPO MOD TURBULENCE
OVER THESE SAME AREAS.

ALSO...AIRMET SIERRA REMAINS IN EFFECT FOR MT OBSC ALONG N AND E
FACING SLOPES BETWEEN UPOLU POINT AND CAPE KUMUKAHI ON THE BIG
ISLAND...AND WILL LIKELY REMAIN IN PLACE THROUGH TONIGHT WITH
ABUNDANT MOISTURE MOVING IN FROM THE E.

PASSING SHRA WILL BRING BRIEF MVFR CIG/SHRA TO MOST WINDWARD
TERMINALS...EXCEPT AT PHTO...WHERE MVFR CIG WILL LIKELY PREVAIL
THROUGH THE NIGHT. LOW-LEVEL WIND SHEAR IS ALSO LIKELY AT PHKO...
WITH STRONG TRADE WINDS JUST ABOVE THE SURFACE OVERLYING A DIURNAL
WEAK LAND/SEA BREEZE CIRCULATION.

&&

.MARINE...
THE GALE WARNING FOR THE ALENUIHAHA AND PAILOLO CHANNELS WILL
CONTINUE THROUGH EARLY THURSDAY MORNING. WINDS OF 25 TO 30 KT ARE
OCCURRING OVER MOST OF THE REMAINDER OF THE HAWAIIAN WATERS. IN
ADDITION...LOCALLY GENERATED WAVES DUE TO THE FRESH TO STRONG TRADE
WINDS...COMBINED WITH A SMALL TO MODERATE NORTHWEST SWELL...ARE
EXPECTED TO KEEP SEAS NEAR 10 FEET OVER MOST OF THE HAWAIIAN COASTAL
WATERS INTO THURSDAY NIGHT. THESE SEAS ALONG WITH THE GUSTY TRADES
REQUIRE A SMALL CRAFT ADVISORY /SCA/ TO REMAIN IN EFFECT FOR ALL
HAWAIIAN COASTAL WATERS AND THE REMAINING CHANNELS INTO EARLY FRIDAY
MORNING. NOTE THAT THE GALE WARNING FOR THE TWO CHANNELS WILL BE
REPLACED WITH A SCA ONCE IT EXPIRES. FURTHER EXTENSIONS OF THE SCA
FOR MUCH OF THE COASTAL WATERS ARE LIKELY THROUGH MOST OF THE
HOLIDAY WEEKEND DUE TO PERSISTENT FRESH TO STRONG TRADES.

A HIGH SURF ADVISORY REMAINS IN EFFECT UNTIL EARLY SATURDAY MORNING
FOR EAST FACING SHORES OF ALL ISLANDS EXPOSED TO THE TRADE WIND
GENERATED WAVES. THESE SHORT-PERIOD WAVES ARE PRODUCING ROUGH AND
CHOPPY SURF CONDITIONS. THESE ELEVATED WAVES WILL LIKELY CONTINUE TO
AFFECT EAST FACING SHORES BEYOND SATURDAY MORNING...SO EXPECT THIS
HIGH SURF ADVISORY TO BE EXTENDED FOR AT LEAST ANOTHER DAY OR TWO
LATER THIS WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 700 AM HST SATURDAY FOR EAST FACING SHORES
OF KAUAI...OAHU...MOLOKAI...MAUI AND THE BIG ISLAND.

WIND ADVISORY UNTIL 600 PM HST THURSDAY FOR HALEAKALA SUMMIT.

GALE WARNING UNTIL 600 AM HST THURSDAY FOR THE PAILOLO AND
ALENUIHAHA CHANNELS.

SMALL CRAFT ADVISORY UNTIL 600 AM HST FRIDAY FOR ALL REMAINING
HAWAIIAN WATERS.

&&

DISCUSSION/MARINE...HOUSTON
AVIATION...BIRCHARD/HOUSTON