Heavy Rain in Hawaii, November 24, 2014

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
940 PM HST SUN NOV 23 2014

.UPDATE...
WINDS AT THE BIG ISLAND SUMMITS HAVE REACHED ADVISORY LEVELS...
SUSTAINED WINDS OF 45 MPH WITH HIGHER GUSTS...FOR WHICH A WIND
ADVISORY IS NOW EFFECT THROUGH MONDAY 6 PM HST. THE PREVIOUS
DISCUSSION FROM 840 PM HST REMAINS THE SAME.

&&

.SYNOPSIS...
A WEAKENING COLD FRONT WILL MOVE ACROSS THE ALOHA STATE FROM LATE
TONIGHT AND THROUGH MONDAY...BRINGING A BRIEF ROUND OF SHOWERS.
COOLER...DRIER AIR AND STRONGER NORTHERLY WINDS WILL FOLLOW THE
FRONT...WITH WINDS TURNING NORTHEAST ON TUESDAY. LOCALLY BREEZY
TRADES WILL THEN CONTINUE THROUGH THE WEEK...BRINGING BRIEF WINDWARD
AND MAUKA SHOWERS.

&&

.DISCUSSION...
A SHARP MID/UPPER LVL TROUGH IS MIGRATING E/SE AT ABOUT 30 MPH
ACROSS THE N CENTRAL PACIFIC AS A SFC COLD FRONT BOUNDARY
APPROACHES KAUAI FROM THE NW. MEANWHILE...SFC HIGH PRESSURE REMAINS
CENTERED FAR NE OF THE AREA...WITH AN ASSOCIATED SFC RIDGE EXTENDING
INTO THE SE PORTIONS OF THE ALOHA STATE.

CLOUDS AND SHOWERS FROM EARLIER AFTERNOON SEA BREEZE CONVECTION ARE
STILL LINGERING OVER THE SMALLER ISLANDS. BUT WITH A RELATIVELY DRY
PROFILE FOR THE MID LVLS...A PERSISTING INVERSION AROUND 7 KFT AND
PWATS BELOW 1 INCH...SHOWERS REMAIN GENERALLY LIGHT TO MODERATE AND
SHORT-LIVED SO FAR. THE ARRIVAL AND PASSAGE OF THE COLD FRONT SHOULD
HELP IN ENHANCING SHOWER COVERAGE THROUGH MON MORNING...STARTING
OVER KAUAI COUNTY TONIGHT AND SPREADING DOWN THE ISLAND CHAIN
THROUGH TOMORROW.

LATEST ECMWF SOLUTION BRINGS THE FROPA A LITTLE EARLIER THAN THE
REST OF THE GUIDANCE...BUT MODEL CONSENSUS IN GENERAL REMAINS FAIR
REGARDING OVERALL TIMING AND IMPACTS OF THE EVENT. THE BULK OF THE
GUIDANCE SHOW A DEVELOPING PREFRONTAL SHOWER BAND NEAR MAUI COUNTY
LATER TONIGHT AS THE COLD FRONT REACHES KAUAI...WHICH SEEMS
REASONABLE AT THIS TIME AS SOME PERSISTENT CLOUDS BANDS JUST
S OF OAHU ARE GRADUALLY BECOMING BETTER ORGANIZED. IN TERMS OF
WEATHER IMPACTS...THE STRONG UPPER LEVEL DYNAMIC SUPPORT IS
EXPECTED TO REMAIN WELL TO THE N OF THE ISLANDS AS THE
AFOREMENTIONED TROUGH CONTINUES TO MIGRATE E DURING THE NEXT COUPLE
OF DAYS. A BRIEF SPIKE IN LOW LVL MOISTURE SHOULD ACCOMPANY THE
FROPA...BUT QUICKLY DROP BEHIND IT. THEREFORE...EXPECT MAINLY
MODERATE SHOWERS...WITH POTENTIAL FOR A FEW PERIODS OF LOCALIZED
HEAVY RAIN ESPECIALLY OVER MOUNTAIN AREAS.

THE FRONT WILL CONTINUE TO WEAKEN AS IT MOVES FARTHER DOWN THE
ISLAND CHAIN...BREAKING DOWN BY THE TIME IT REACHES THE BIG ISLAND
ON MON. WINDS AHEAD OF THE FRONT WILL TURN TO THE SW AND W...THEN
STRENGTHENING AND TURN FROM THE N BEHIND THE FROPA MON AFTERNOON.
OVERALL CONDITIONS WILL BECOME MUCH DRIER AND GUSTY LATE MON THROUGH
TUE...WITH DEWPOINTS DROPPING INTO THE UPPER 50S.

STRONG HIGH PRESSURE WILL BUILD N OF THE ISLANDS IN THE WAKE OF THE
TROUGH...KEEPING A MODERATE TO LOCALLY FRESH TRADE WIND REGIME
ACROSS THE AREA THROUGH THE REST OF THE WEEK. LOW LEVEL MOISTURE
SHOULD GRADUALLY RECOVER DURING THE SECOND HALF OF THE WEEK WITH
SHOWER ACTIVITY SHIFTING OVER WINDWARD AND MAUKA AREAS.

&&

.AVIATION...
WIDELY SCATTERED SHOWERS AND ISOLATED MVFR CEILINGS WILL CONTINUE
ACROSS THE SMALLER ISLANDS THIS EVENING...AHEAD OF AN APPROACHING
FRONT. A BAND OF CLOUDS AND SHOWERS ALONG THE FRONT WILL REACH KAUAI
AFTER MIDNIGHT AND OAHU AROUND SUNRISE...THEN CONTINUE MOVING
SOUTHEAST TO MAUI COUNTY BY MONDAY AFTERNOON. AREAS OF MVFR
CONDITIONS WILL BE POSSIBLE WITHIN THIS FRONTAL BAND. AIRMET
SIERRA FOR MOUNTAIN OBSCURATION MAY BECOME NECESSARY ACROSS WESTERN
AND CENTRAL PARTS OF THE STATE LATER TONIGHT INTO MONDAY MORNING...
AND THIS POTENTIAL HAS BEEN MENTIONED IN THE OUTLOOK OF THE CURRENT
AIRMET BULLETIN. THE FRONT WILL BE WEAKENING AS IT MOVES SOUTHEAST
AND MAY DISSIPATE BEFORE REACHING THE BIG ISLAND LATE MONDAY.

A TROUGH ALOFT WILL BE DIGGING SOUTHEAST TOWARD THE AREA THROUGH
THE NIGHT...THEN PASSING ACROSS THE STATE ON MONDAY. HORIZONTAL AND
VERTICAL WIND SHEAR ASSOCIATED WITH THE TROUGH MAY PRODUCE
TURBULENCE ALOFT AFTER MIDNIGHT THROUGH MONDAY. THIS POTENTIAL
HAS ALSO BEEN MENTIONED AS AN OUTLOOK IN THE CURRENT AIRMET.

&&

.MARINE...
THE COMBINATION OF INCREASING WINDS AND WIND WAVES AND THE ARRIVAL
OF A LONGER PERIOD SWELL MAY BRING SMALL CRAFT ADVISORY CONDITIONS
MONDAY THROUGH TUESDAY OVER MOST MARINE ZONES...ESPECIALLY THE
TYPICALLY WINDIER AREAS NEAR MAUI COUNTY AND THE BIG ISLAND.

THE INCOMING NORTH-NORTHWEST SWELL PEAKED AT BUOY 51101
EARLIER...AND IT HAS BEEN SLIGHTLY LAGGING WAVEWATCH III
GUIDANCE...WHICH ALREADY ONLY SHOWED SURF APPROACHING ADVISORY
LEVELS FOR NORTH FACING SHORES. A REINFORCEMENT TO THIS SWELL IS
EXPECTED LATE MONDAY INTO MONDAY NIGHT...WHICH MAY PUSH US ABOVE
ADVISORY LEVELS. BREEZY TRADE WINDS LATER IN THE WEEK WILL PRODUCE
CHOPPY SURF ALONG EAST FACING SHORES...BUT IS EXPECTED TO REMAIN
BELOW ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST MONDAY FOR THE BIG ISLAND SUMMITS.

&&

DISCUSSION/MARINE...REYNES
AVIATION...JACOBSON