Prognostic Meteorological Discussion
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FXHW01 KWNH 141220
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
719 AM EST THU DEC 14 2017

VALID 00Z FRI DEC 15 2017 - 00Z FRI DEC 22 2017

...HEAVY RAIN THREAT NEXT WEEK...

AN UPPER LOW WILL EAST OF THE ISLANDS WILL SLOWLY DRIFT
WEST-NORTHWESTWARD TOMORROW INTO SATURDAY, PASSING JUST NORTH OF
OAHU. BY SUNDAY THE UPPER LOW IS FORECAST TO LIFT NORTHWARD AND
BECOME ABSORBED INTO THE FLOW AHEAD OF AN APPROACHING TROUGH FROM
THE NORTHWEST. THAT TROUGH MAY CLOSE OFF ONE OR TWO UPPER LOWS
EARLY NEXT WEEK - ONE TO THE NORTH OF THE REGION AROUND 35N/160W
AND PERHAPS ANOTHER TO THE NORTHWEST OF THE KAUAI. GFS/UKMET WERE
QUICKER WITH THE TROUGH THAN THE ECMWF/CANADIAN BUT GIVEN THE
UNCERTAINTY IN EVOLUTION PREFER A CONSENSUS POSITION BETWEEN THE
TWO CAMPS WHICH IS A BIT SLOWER THAN THE ENSEMBLE MEANS. ENSEMBLES
AND MOST DETERMINISTIC SOLUTIONS THEN SHOW REINFORCING TROUGHING
FROM THE NORTHWEST NEXT WED/THU WITH PERHAPS YET ANOTHER UPPER LOW
JUST TO THE NORTH OF THE REGION.

BREEZY NORTHEAST MAY EXCEED 30 KTS WITH HIGHER GUSTS INTO TOMORROW
MORNING BEFORE THE CLOSED LOW APPROACHES FROM THE EAST. MOISTURE
WILL WRAP BACK AROUND THE SURFACE LOW FROM THE NORTH BUT THE
HEAVIEST RAIN ON THE EAST SIDE OF THE UPPER LOW WILL REMAIN
DISPLACED TO THE NORTHEAST OF THE REGION OVER THE NEXT SEVERAL
DAYS.

THE NEXT UPPER TROUGH OR WEAK UPPER LOW NEXT WEEK WILL LIKELY DRAW
DEEP TROPICAL MOISTURE FROM THE ITCZ AND HAS THE POTENTIAL FOR
MUCH MORE PRECIPITATION GIVEN ITS LOCATION. DETERMINISTIC MODELS
STILL SHOW SEVERAL INCHES OF RAIN OVER SOME OF THE ISLANDS NEXT
TUE-THU AHEAD OF THE FRONT WELL TO THE NORTHWEST. 00Z ECMWF
ENSEMBLES AND 06Z GEFS ENSEMBLES NOW SHOW A PROBABILITY OF AT
LEAST AN INCH OF PRECIPITATION EXCEEDING 60-80% IN THE 72 HRS
ENDING 00Z/22 OVER THE BIG ISLAND AND MAUI. THIS WAS A BIG
INCREASE FROM JUST 24 HRS AGO.


FRACASSO


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