Heavy Rain in Hawaii, February 16 to 17, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1012 AM HST TUE FEB 16 2016

.SYNOPSIS...
STRONG HIGH PRESSURE BUILDING TO THE NORTHWEST WILL PRODUCE
LOCALLY WINDY TRADES THROUGH TONIGHT. MOISTURE FROM A DISSIPATED
FRONTAL BOUNDARY WILL CONTINUE TO PRODUCE SHOWERS ON KAUAI THROUGH
THE DAY THEN PUSH OVER THE REST OF THE ISLAND CHAIN THROUGH
TONIGHT. RAINFALL WILL BE FOCUSED ALONG WINDWARD SLOPES WITH
SHOWERS PERIODICALLY REACHING LEEWARD AREAS AT TIMES. DRIER
WEATHER AND LIGHTER TRADE WINDS ARE EXPECTED FOR THE LATER PART OF
THE WEEK... FOLLOWED BY A POTENTIAL FRONTAL PASSAGE THIS WEEKEND.

&&

.DISCUSSION...
THE MAIN FEATURES AFFECTING HAWAIIAN WEATHER FOR THE NEXT 24 HOURS
ARE A NEARLY STATIONARY 1035 MB HIGH CURRENTLY CENTERED ABOUT
1200 MILES NORTHWEST OF THE STATE AND A SLOW-MOVING...DISSIPATED
FRONTAL BOUNDARY...OR SHEAR LINE...CURRENTLY DRAPED ACROSS KAUAI.

SHOWERS ALONG THE LEADING EDGE OF THE FRONTAL BOUNDARY ARE PASSING
OVER THE NORTHERN HALF OF OAHU THIS MORNING WITH THE BULK OF THE
MOISTURE FOCUSED ON KAUAI...WHERE A STEADY SUPPLY OF SHOWERS IS
EXPECTED THROUGH THE DAY. ALTHOUGH THERE IS AN UPPER LEVEL TROUGH
OVER AN JUST WEST OF KAUAI...MID LEVEL RIDGING OVERHEAD IS KEEPING
THE MOISTURE CAPPED MAINLY BELOW 15000 FT AND WILL MINIMIZE ANY
FLOOD THREAT. THE BOUNDARY WILL BE PUSHED SLOWLY DOWN THE ISLAND
CHAIN TONIGHT AND WEDNESDAY AS HIGH PRESSURE BUILDS A BIT
EASTWARD. RAINFALL WILL BE FOCUSED ALONG WINDWARD SLOPES WITH
SOME SHOWERS PERIODICALLY REACHING LEEWARD AREAS AT TIMES.

LOCALLY WINDY CONDITIONS ARE EXPECTED THROUGH AT LEAST TONIGHT.
THE RADAR VAD WIND PROFILE ON KAUAI HAS BEEN DETECTING 30 TO 35
KT WINDS IN THE LOWEST 8000 FT THIS MORNING...WHILE LIHUE AIRPORT
HAS BEEN REPORTING SUSTAINED WINDS NEAR 30 MPH. MEANWHILE...A
HANDFUL OF OBSERVING SITES ON THE OTHER ISLANDS ARE SEEING WIND
GUSTS IN EXCESS OF 40 MPH. AS THE HIGH TO THE NORTHWEST BUILDS
SLIGHTLY EASTWARD...THE GFS AND ECMWF SHOW WINDS AT 850 MB EDGING
UPWARD BY ABOUT 5 KT IN THE NEXT 12 HOURS. THIS SHOULD BE ENOUGH
TO PRODUCE LOCALIZED WIND GUSTS TO 50 MPH AROUND AND DOWNWIND OF
ISLAND TERRAIN...AND THE WIND ADVISORY HAS BEEN EXPANDED TO COVER
MOST AREAS THROUGH TONIGHT.

TRADE WINDS WILL BE IN THE BREEZY TO BORDER LINE LOCALLY WINDY
RANGE ON WEDNESDAY AS THE RIDGE TO THE NORTH BEGINS TO WEAKEN.
SHOWER ACTIVITY WILL DIMINISH FROM NORTH TO SOUTH AS THE BAND OF
MOISTURE BECOMES FOCUSED ALONG BIG ISLAND SLOPES.

A SLOW DECLINE IN TRADE WINDS IS EXPECTED ON THURSDAY AND
FRIDAY AS AN APPROACHING FRONT WEAKENS THE RIDGE TO OUR NORTH.
ANOTHER FRONT WILL AFFECT THE STATE THIS WEEKEND.

&&

.AVIATION...
STRONG HIGH PRESSURE TO THE NW WILL KEEP THE STRONG AND GUSTY NE
TRADE WINDS OVER THE AREA INTO WEDNESDAY. THE PHKI...PHMO...AND PHMK
RADAR VAD WIND PROFILES SHOW WINDS BETWEEN 20 AND 30 KT UP TO 10
KFT...WITH ISOLATED 35 KT RECORDINGS AT PHKI. AIRMET TANGO IS POSTED
FOR TEMPO MOD LOW LEVEL TURB OVER AND S THROUGH W OF THE MOUNTAINS.
PIREP REPORTS THUS FAR HAVE ONLY INDICATED LIGHT TO MOD TURB. TAKE
NOTE...SIGMET FOR SEV TURB MAY BE NEEDED AT TIMES AND SOME TAFS MAY
NEED TO INCLUDE LLWS. ADDITIONALLY...AIRMET TANGO IS ALSO POSTED FOR
STRONG SURFACE WIND AROUND THE BIG ISLAND...ALENUIHAHA AND PAILOLO
CHANNELS...LANAI...AND KAHOOLAWE. THE ENHANCED TRADE WINDS WILL HELP
PUSH MOISTURE ASSOCIATED WITH THE DISSIPATED FRONTAL BAND BACK OVER
THE ISLANDS.

INCREASED CLOUDS AND SHOWERS ASSOCIATED WITH A DISSIPATED FRONTAL
BOUNDARY ARE STRETCHING BETWEEN OAHU AND KAUAI THIS MORNING. AIRMET
SIERRA FOR MOUNTAIN OBSC IS POSTED OVER KAUAI. THIS WILL LIKELY STAY
POSTED AT LEAST INTO THE AFTERNOON AND MAY NEED TO BE EXPANDED OVER
OAHU AND MAUI COUNTY LATER. OTHERWISE TRADE WINDS WILL HELP FOCUS
CLOUDS AND SHOWERS ALONG WINDWARD AND MOUNTAIN AREAS...INTRODUCING
PERIODS OF MVFR IN PASSING CLOUDS AND SHOWERS.

&&

.MARINE...
THE GALE WARNING WAS EXPANDED FROM BIG ISLAND WATERS TO INCLUDE
THE PAILOLO CHANNEL...AND A SMALL CRAFT ADVISORY /SCA/ COVERS THE
REMAINING WATERS AROUND THE STATE. TRADE WINDS COULD STRENGTHEN A
BIT MORE IN THE NEXT 12 HOURS...AND THE GALE WARNINGS MAY NEED TO
BE EXTENDED THROUGH THE DAY ON WEDNESDAY. AT MINIMUM...SCA
CONDITIONS FOR WINDS AND ROUGH SEAS WILL PERSIST INTO THURSDAY.

STRONG TRADE WINDS WILL CONTINUE TO BRING ELEVATED ROUGH SURF ALONG
EAST FACING SHORES...WHERE A HIGH SURF ADVISORY REMAINS IN EFFECT.
A MODERATE NORTHWEST SWELL IS EXPECTED FRIDAY...WITH A LARGE
NORTHWEST SWELL IS POSSIBLE LATE SUNDAY THROUGH MONDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 AM HST WEDNESDAY FOR ALL ISLANDS.

HIGH SURF ADVISORY UNTIL 6 PM HST WEDNESDAY FOR EAST FACING SHORES.

GALE WARNING UNTIL 6 AM HST WEDNESDAY FOR PAILOLO CHANNEL-
ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND
SOUTHEAST WATERS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY FOR ALL REMAINING
WATERS AND CHANNELS.

&&

WROE