Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 011954
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SUN MAR 1 2015

.SYNOPSIS...
A TROUGH WILL CREATE MOIST AND UNSTABLE CONDITIONS OVER THE BIG
ISLAND AND MAUI THROUGH TOMORROW. HIGH PRESSURE NORTHWEST OF THE
AREA WILL PRODUCE LOCALLY BREEZY TRADE WINDS FOCUSING CLOUDS AND
SHOWERS OVER WINDWARD SLOPES FROM MOLOKAI TO KAUAI. SHOWERY TRADE
WIND WEATHER WILL CONTINUE THROUGH AT LEAST MID WEEK...ESPECIALLY ON
MAUI AND THE BIG ISLAND.

&&

.DISCUSSION...
A TROUGH NEAR THE BIG ISLAND IS CREATING UNSTABLE CONDITIONS. THE
200 AM BALLOON SOUNDING FROM HILO SOUNDING SHOWED NO INVERSION AND A
NEARLY SATURATED ATMOSPHERE BELOW 25000 FT WITH PRECIPITABLE
WATER...PW...VALUES OVER 1.6 INCHES. THE ATMOSPHERE IS MUCH DRIER
AND MORE STABLE FARTHER WEST. THE 200 AM SOUNDING FROM LIHUE SHOWED
A TEMPERATURE INVERSION AROUND 7000 FT AND PW LESS THAN AN INCH.
LIGHTNING...RADAR AND SATELLITE DATA SHOWED THUNDERSTORMS...SOME
HEAVY...OVER WATER JUST EAST OF MAUI AND THE BIG ISLAND THROUGH
AROUND 900 AM THIS MORNING. THE THUNDERSTORMS HAVE DISSIPATED IN
THE PAST HOUR BUT HEAVY SHOWERS PERSIST. SHOWERS OVER WATER OFTEN
WEAKEN AFTER SUNRISE. SHOWERS MAY BECOME MORE ACTIVE OVER THE
SLOPES OF THE BIG ISLAND AND MAUI LATER TODAY AS THE LAND HEATS UP.

A SURFACE TROUGH WILL PERSIST NEAR THE BIG ISLAND...KEEPING ENHANCED
LOW LEVEL MOISTURE IN PLACE. A JET STREAM ALOFT WILL REMAIN NEAR THE
ISLANDS...BUT THE DIFFLUENT PORTION OF THE JET WILL SHIFT SLOWLY
EAST...PUSHING HIGH CLOUDS AND GREATEST INSTABILITY EAST OF THE
STATE. HOWEVER...A MID LEVEL TROUGH WILL REMAIN STALLED ACROSS THE
CENTRAL PORTION OF THE STATE...AND WITH 500 MB TEMPS REMAINING VERY
COLD AT -12 TO -14C...THE ATMOSPHERE WILL CONTINUE TO BE UNSTABLE
NEAR THE BIG ISLAND AND POSSIBLY MAUI. AS A RESULT...ISOLATED
THUNDERSTORMS AND HEAVY SHOWERS REMAIN A THREAT...AND SOME
THUNDERSTORMS COULD BE STRONG TODAY. WINTER WEATHER REMAINS A THREAT
ON THE BIG ISLAND SUMMITS ABOVE 12500 FT. CONVECTION DEVELOPING
OVER THE SLOPES MAY PRODUCE MORE SNOW SHOWERS THIS AFTERNOON.

THE SURFACE TROUGH NEAR THE BIG ISLAND WILL SLOWLY WEAKEN AND SHIFT
NORTHEAST THROUGH MID-WEEK WHILE HIGH PRESSURE STRENGTHENS TO THE
NORTHWEST. THAT WILL ALLOW TRADE WINDS TO SPREAD ACROSS THE ENTIRE
STATE. LOW LEVEL MOISTURE WILL INITIALLY BE HIGHEST OVER THE
BIG ISLAND AND MAUI...BUT THE GFS SUGGESTS AN INCREASE IN MOISTURE
OVER OAHU AND KAUAI...LIKELY PRODUCING A WET TRADE WIND PATTERN.
TROUGHING ALOFT WILL ALSO LINGER...RAISING THE POSSIBILITY OF
CONTINUED INSTABILITY...BUT CONFIDENCE IS NOT HIGH ENOUGH AT THIS
TIME TO INCLUDE HEAVY SHOWERS.

THE GFS AND ECMWF MODELS BOTH MODELS SHOW A DEEP TROUGH ALOFT
DEVELOPING NORTHEAST OF THE ISLANDS NEXT WEEKEND WITH A STRONG
SURFACE HIGH NORTHWEST OF THE AREA. BOTH MODELS SHOW A LONG WEST
SOUTHWEST TO EAST NORTHEAST BAND OF SHOWERS FORMING IN THE
TRADE-WIND FLOW ACROSS THE CENTRAL PACIFIC. THE GFS SHOWS AN AREA OF
RAIN ALONG THIS BAND SPREADING OVER THE ISLANDS FROM THE SOUTHWEST
AROUND NEXT SATURDAY NIGHT. THE ECMWF KEEPS THE RAIN BAND SOUTHEAST
OF THE ISLANDS THROUGH NEXT WEEKEND. IT IS TOO SOON TO SAY WHICH
MODEL MIGHT BE BETTER SO CONFIDENCE IN THE FORECAST FOR NEXT WEEKEND
REMAINS LOW.

&&

.AVIATION...
AIRMET SIERRA IS POSTED FOR MTN OBSC OVER N THRU E SECTIONS OF THE
BIG ISLAND...MAUI...AND MOLOKAI. SHOWERS HAVE NOT BEEN AS ACTIVE
OVER MOLOKAI...HOWEVER...LOW CEILINGS PERSIST. THE SLIGHT CHANCE OF
THUNDERSTORMS REMAINS OVER MAUI AND THE BIG ISLAND TODAY. CLOUD TOPS
TO FL350 AND IFR CONDITIONS CAN BE EXPECTED IN THUNDERSTORMS.

VFR CONDITIONS WILL PREVAIL OVER OAHU AND KAUAI WITH SHOWERS MOVING
OVER THOSE ISLANDS FROM THE NORTH-NORTHEAST. TEMPO MVFR IS POSSIBLE
IN THESE SHOWERS.

AIRMET TANGO FOR TEMPO MOD TURB BETWEEN FL250 AND FL350 REMAINS OVER
MAUI AND THE BIG ISLAND DUE TO A STRONG SW TO NE JET STREAM.

&&

.MARINE...
A NORTH TO SOUTH SURFACE TROUGH REMAINS NEAR THE BIG ISLAND. THIS IS
PRODUCING GENTLE WINDS AROUND THE BIG ISLAND WITH FRESH TO STRONG
NORTHEAST TRADE WINDS OVER THE SMALLER ISLANDS. THESE WINDS WILL
BUILD SOUTHEAST OVER THE BIG ISLAND LATER TODAY. A SMALL CRAFT
ADVISORY FOR LOCALLY STRONG WINDS BEGINS THIS MORNING FOR WATERS
NEAR KAUAI...AND CHANNELS NEAR THE BIG ISLAND AND MAUI COUNTY. IN
ADDITION...THE THREAT OF THUNDERSTORMS...SOME POSSIBLY STRONG...WILL
CONTINUE OVER WATERS NEAR THE BIG ISLAND AND MAUI THROUGH THE DAY.

A NORTH NORTHWEST SWELL WILL BUILD TODAY...PRODUCING NORTH SHORE
SURF AROUND THE ADVISORY LEVEL LATE TONIGHT AND MONDAY. SMALLER
NORTH NORTHWEST SWELLS ARE DUE NEXT WEEK. SEE THE COLLABORATIVE
NEARSHORE SWELL AND WIND FORECAST FOR MORE DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 600 AM MONDAY FOR THE SUMMITS OF MAUNA
KEA AND MAUNA LOA ON THE BIG ISLAND.

SMALL CRAFT ADVISORY FROM 900 AM TODAY TO 900 AM MONDAY FOR WATERS
AROUND KAUAI AND WATERS AROUND MAUI.

&&

$$
DONALDSON




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