Heavy Rain in Hawaii, February 1, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
835 PM HST SAT JAN 31 2015

.SYNOPSIS...
LIGHT TO MODERATE TRADES WILL CONTINUE TONIGHT AS WEAK SURFACE HIGH
PRESSURE REMAINS TO THE NORTH OF THE MAIN HAWAIIAN ISLANDS. WINDS
WILL BEGIN TURNING TO THE SOUTHWEST LATE MONDAY AS A FRONT
APPROACHES THE AREA FROM THE NORTHWEST. ADDITIONAL FRONTS MAY IMPACT
THE ISLANDS NEXT WEEK WITH PREVAILING WEST TO NORTHWEST WINDS DURING
THE SECOND HALF OF THE WEEK. SHOWERS WILL FAVOR WINDWARD AND MAUKA
AREAS ON SUNDAY...THEN SPREADING INTO LEEWARD AREAS AS THE VARIOUS
FRONTS REACH THE ISLANDS NEXT WEEK.

&&

.DISCUSSION...
HIGH PRESSURE REMAINS TO THE N OF THE MAIN HAWAIIAN ISLANDS...
KEEPING A LIGHT TO MODERATE TRADE WIND PATTERN ACROSS THE AREA
TONIGHT AND THROUGH SUN NIGHT. MAUKA SHOWERS CAN BE OBSERVED
LINGERING OVER WINDWARD MAUI...WITH LOCALIZED HEAVY RAIN AFFECTING
COASTAL LOCATIONS FROM HUELO TO HANA. A FLOOD ADVISORY WAS ISSUED
FOR THESE LOCATIONS...WHICH WILL REMAIN IN EFFECT THROUGH 945 PM HST
TONIGHT.

THE TRADES WILL PREVAIL UNTIL MON WHEN AN APPROACHING COLD FRONT
BOUNDARY FROM THE NW WILL VEER WINDS TO A MORE SE FLOW. LATEST ECMWF
SOLUTION BRINGS THE LEADING EDGE OF THE FRONT INTO THE NW PORTIONS
OF THE ALOHA STATE BY LATE MON NIGHT AND MOVING DOWN THE ISLAND
CHAIN THROUGH TUE. SHOWERS WILL INCREASE WITH THE FROPA...EXPECTING
THE BULK OF THE RAIN MON NIGHT AND TUE. BUT WITH THE PARENT LOW
REMAINING WELL TO THE N OF THE ISLANDS...DYNAMIC SUPPORT FOR THIS
EVENT WILL BE POOR...WHICH WILL KEEP RAINFALL IN GENERAL IN THE
MODERATE CATEGORY. ALTHOUGH LOCALIZED EPISODES OF HEAVY RAIN ARE
CERTAINLY POSSIBLE.

AS WAS THE CASE WITH THE PREVIOUS FORECAST PACKAGE...THE FORECAST
PHILOSOPHY REMAINS CLOSER TO THE ECMWF SOLUTION AS GFS STILL SHOWS
RATHER STRONGER WINDS IN THE WAKE OF THE FROPA. THE FORECAST WILL BE
ADJUSTED ACCORDINGLY AS NEW MODEL RUNS BECOME AVAILABLE...BUT FOR
NOW WILL KEEP ECMWF AS THE PREFERRED SOLUTION FOR THE SHORT RANGE
FORECAST. EXPECT W AND NW WINDS TO QUICKLY ESTABLISH BEHIND THE
FRONT...WITH A COUPLE MORE FRONTS ALSO MOVING JUST TO THE N OR
ACROSS THE AREA DURING THE SECOND HALF OF NEXT WEEK. TIMING STILL
REMAINS RATHER UNCERTAIN IN GUIDANCE...BUT IN GENERAL...EXPECT
ANOTHER FRONTAL SYSTEM APPROACHING OR REACHING THE AREA AROUND
WED/WED NIGHT. YET ANOTHER FRONT WILL BE MOVING JUST TO THE NW OF
THE ISLAND CHAIN IN THE LATE THU/FRI TIMEFRAME. SHOWER ACTIVITY WILL
INCREASE WITH EACH OF THESE SYSTEMS.

MODELS FINALLY BRING BUILDING SFC HIGH PRESSURE OVER THE AREA BY
NEXT WEEKEND...BRINGING LIGHT TRADES AND DRIER CONDITIONS FOR THE
LATER PART OF THE LONG RANGE FORECAST.

&&

.AVIATION...
A WEAK RIDGE OF HIGH PRESSURE JUST NORTH OF THE ISLANDS WILL KEEP A
LIGHT WIND REGIME IN PLACE THROUGH SUNDAY...DOMINATED BY OVERNIGHT
LAND BREEZES AND DAYTIME SEA BREEZES. BEST CHANCES FOR MVFR CIGS
AND -SHRA WILL BE AT PHTO OVERNIGHT. MVFR CIGS ARE EXPECTED AT PHNY
ON SATURDAY...AND MAY ALSO IMPACT PHMK AS WELL. ISOLATED TO
SCATTERED SHRA ARE EXPECTED TO DEVELOP OVER WINDWARD AND MAUKA
AREAS SUNDAY AFTERNOON AS WELL...WITH SOME BRIEF VSBY RESTRICTIONS
POSSIBLE.

AN AIRMET IS CURRENTLY IN EFFECT FOR OAHU...MAUI AND MOLOKAI THROUGH
07Z. THIS AIRMET WILL LIKELY NEED TO BE CONTINUED FOR MAUI THROUGH
10Z. WILL NEED TO KEEP AN EYE ON SOME OF THE MID-LEVEL CLOUD MOVING
INTO KAUAI AS WELL FOR THE POSSIBILITY OF NEEDING AN AIRMET FOR SOME
LIGHT ICING.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS IN EFFECT THROUGH THE REST OF
TONIGHT...WITH THE NW SWELL EXPECTED TO BEGIN DECREASING ON SUNDAY.
HOWEVER...IF BUOY OBSERVATIONS DO NOT SHOW A CLEAR DOWNWARD TREND
ON THIS SWELL...THE ADVISORY COULD BE EXTENDED IF NECESSARY.

THE CURRENT SWELL IS ALSO PRODUCING COMBINED SEAS IN EXCESS OF 10
FT...SO A SMALL CRAFT ADVISORY /SCA/ REMAINS POSTED FOR AREAS
EXPOSED TO THE SWELL. WHILE WINDS ARE EXPECTED TO REMAIN BELOW SCA
LEVELS THIS WEEKEND...AHEAD OF THE NEXT FRONT...WINDS MAY REACH SCA
LATE MONDAY PARTICULARLY NEAR KAUAI...OAHU AND MOLOKAI.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU...KAUAI...OAHU...AND MOLOKAI...AND FOR NORTH
FACING SHORES OF MAUI.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SUNDAY FOR THE WATERS
SURROUNDING KAUAI...THE OAHU WINDWARD WATERS...THE KAIWI CHANNEL AND
THE MAUI COUNTY WINDWARD WATERS.

&&

DISCUSSION/MARINE...REYNES
AVIATION...JELSEMA