Heavy Rain in Hawaii, March 30 to 31, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
930 AM HST SAT MAR 30 2013

.SYNOPSIS...
SHOWERS WILL AFFECT MUCH OF THE AREA TODAY AS A COLD FRONT MOVES
ACROSS THE ISLANDS. THE UNSETTLED WEATHER WILL BEGIN CLEARING OUT
LATE IN THE AFTERNOON AND EARLY THIS EVENING OVER KAUAI AND
OAHU...THEN MAUI COUNTY AND THE BIG ISLAND ON SUNDAY. COOLER AND
DRIER NORTHERLY FLOW WILL FOLLOW THE FRONTAL PASSAGE...AND PERSIST
THROUGH THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
LIGHT AND VARIABLE WINDS ACROSS THE AREA CONTINUE TODAY AS A
WEAKENING COLD FRONT MOVES ACROSS THE MAIN HAWAIIAN ISLANDS. SHOWERS
WILL AFFECT MOST OF THE AREA.

THE FRONT IS BEING DRIVEN BY A MID/UPPER LVL TROUGH CROSSING THE N
CPAC...WITH ITS AXIS NOW LOCATED JUST N OF THE ISLANDS. THE BEST
DYNAMIC SUPPORT...HOWEVER...IS EXPECTED TO REMAIN N OF THE AREA
WITH NO SIGNIFICANT THUNDERSTORM ACTIVITY EXPECTED WITH THIS EVENT.
CLOUDS AND SHOWERS CONTINUE TO LINGERING OVER MUCH OF THE COASTAL
WATERS THIS MORNING. DOWNSLOPE FLOW OVER THE ISLANDS KEPT MOST
OF THESE SHOWERS OFFSHORE DURING THE OVERNIGHT HOURS. BUT AS THE
FRONT MOVES ACROSS THE ISLAND CHAIN AND DAYTIME HEATING
INTENSIFIES...SHOWERS WILL DEVELOP OVER LEEWARD AND WINDWARD AREAS
THROUGHOUT THE DAY. 12Z HILO AND LIHUE SOUNDINGS DEPICT WEAK AND
ELEVATED INVERSIONS...ALONG WITH INCREASING PWATS...WHICH SUGGESTS
POTENTIAL FOR SHOWERS TO REACH THE BIG ISLAND SUMMITS DURING THE
DAY...AND SOME LIGHT SNOW SHOWERS POSSIBLE TONIGHT. ALSO...PRESSURE
GRADIENTS ALOFT WILL BECOME TIGHTER AS THE TROUGH MOVES TO THE N OF
THE ALOHA STATE...BRINGING STRONG WINDS AT THE BIG ISLAND SUMMITS.
GFS LAYER WINDS FROM 600-500 MB ALSO SUGGEST SUMMIT WIND SPEEDS
REACHING THE 30-35 KT RANGE BY SUN EVENING AND LASTING THROUGH AT
LEAST TUE. THEREFORE...A WIND ADVISORY WILL LIKELY BE ISSUED LATER
TODAY FOR THE BIG ISLAND SUMMITS.

BEHIND THE FROPA...WINDS AT THE SFC WILL INCREASE AND BECOME
GUSTY...MAINLY FROM THE N. THIS WILL USHER DRIER AND COOLER AIR WITH
NIGHTTIME TEMPERATURES DECREASING TO BELOW NORMALS DURING THE NEXT
COUPLE OF DAYS. MODELS STALL THE FRONT JUST TO THE SE OF THE BIG
ISLAND BY MON...AND GRADUALLY BREAKING IT DOWN THROUGH MID WEEK. THE
ROBUST N WINDS WILL CONTINUE THROUGH EARLY NEXT WEEK...THEN SPEEDS
DECREASE AND BECOME GENERALLY LIGHT TO MODERATE BY TUE AS PRESSURE
GRADIENTS RELAX.

A TRADE WIND WEATHER PATTERN WITH LIMITED SHOWERS SHOULD THEN
PREVAIL FOR THE REST OF THE WORK WEEK AS HIGH PRESSURE FILLS IN
NORTH OF THE STATE.

&&

.AVIATION...
A COLD FRONT IS MOVING IN FROM THE NORTHWEST THIS MORNING.
PRE-FRONTAL CONVERGENCE CLOUDS AND SHOWERS STRETCHING FROM MOLOKAI
TO THE BIG ISLAND WILL BRING OCCASIONAL MTN OBSC AND REDUCED
VISIBILITY THROUGH THE MORNING FROM MOLOKAI EASTWARD. THESE CLOUDS
AND SHOWERS WILL LIKELY HANG AROUND INTO THE AFTERNOON FOR MAUI AND
BIG ISLAND. AIRMET SIERRA IS IN EFFECT FOR THE MTN OBSC.

AIRMET ZULU FOR LIGHT RIME ICING IN LYR 110-150 IS IN EFFECT FOR THE
HIGHER TOPPED CLOUDS DUE TO THE RAISED INVERSION LEVEL. NORTHERLY
WINDS WILL FILL IN TODAY BEHIND THE FRONT AND WILL BE MONITORING FOR
MODERATE TURBULENCE. DRIER AIR IS EXPECTED TO FILER IN TONIGHT AND
SUNDAY.

&&

.MARINE...
A NW SWELL WILL BRING HIGH SURF ALONG EXPOSED N AND W FACING SHORES
THIS WEEKEND. A HIGH SURF ADVISORY IS IN EFFECT THROUGH SUNDAY
EVENING. ONLY A SUBTLE DROP IS EXPECTED MON-TUE SO SURF CONDITIONS
WILL STILL BE HAZARDOUS. MUCH LARGER NW SWELL IS EXPECTED THE
SECOND HALF OF NEXT WEEK. ADDITIONALLY...SOUTH FACING BEACHES WILL
SEE A SIGNIFICANT INCREASE FROM THE SOUTHERN HEMISPHERE BY WED.

THE COMBINATION OF INCREASING NW SWELL...N WINDS AND LOCALLY
GENERATED WINDSWELL WILL LIKELY TRIGGER A SMALL CRAFT ADVISORY FOR
WESTERN COASTAL ZONES THIS EVENING.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FROM 6 AM THIS MORNING TO 6 PM HST SUNDAY FOR
NORTH AND WEST FACING SHORES OF KAUAI...AND NORTH FACING SHORES OF
OAHU MOLOKAI AND MAUI.

&&

DISCUSSION/MARINE...REYNES
AVIATION...FOSTER