Prognostic Meteorological Discussion
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000
FXHW01 KWNH 251208
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
808 AM EDT MON MAY 25 2015

VALID 00Z TUE MAY 26 2015 - 00Z TUE JUN 02 2015

GUIDANCE IS AGREEING IN PRINCIPLE WITH A RETROGRESSION OF THE
EAST-CENTRAL PACIFIC MEAN TROUGH.  WITH RESPECT TO INDIVIDUAL
FEATURES THIS PLAYS OUT AS A LEADING TROUGH/UPPER LOW IS CURRENTLY
BEING EJECTED BY ANOTHER SYSTEM SETTLING TO THE NORTH-NORTHEAST OF
THE STATE TUE-FRI.  THEN A SOMEWHAT FLATTER TROUGH SHOULD REACH A
POSITION TO THE NORTH OF THE REGION BY THE START OF NEXT WEEK.
THIS EVOLUTION WILL ENCOURAGE AN INCREASE IN DEEP
MOISTURE/RAINFALL POTENTIAL, WITH PRECIPITABLE WATER VALUES
STARTING OUT IN THE 1-1.25 INCH RANGE AND TRENDING TOWARD AT LEAST
1.25-1.50 INCHES.  BASED ON THE CURRENT ARRAY OF 00Z GEFS/ECMWF
ENSEMBLE MEMBERS, THERE IS A DECENT POSSIBILITY THAT PWATS MAY
EXCEED 1.50 INCHES AT LEAST BRIEFLY SOMETIME WITHIN THE THU-MON
PERIOD.  HOWEVER THE 1.75-2 INCH VALUES IN THE 06Z GFS BY NEXT MON
ARE EXTREME VERSUS THE 00Z ENSEMBLE ENVELOPE.

DURING THE FIRST HALF OF THE PERIOD GENERALLY
NORTHERLY/NORTHEASTERLY WINDS SHOULD LIGHTER THUS ALLOWING LAND
AND SEA BREEZE BOUNDARIES TO HAVE MORE INFLUENCE ON SHOWER
ACTIVITY.  ALSO MOST GUIDANCE IS SUGGESTING A SURFACE TROUGH MAY
BECOME ESTABLISHED OVER THE ISLANDS AND PROVIDE AN ADDED FOCUS FOR
RAINFALL.  LATE IN THE PERIOD SURFACE HIGH PRESSURE BUILDING
TOWARD THE CENTRAL PACIFIC MAY HELP TO FLATTEN THE SURFACE PATTERN
OVER THE ISLANDS A LITTLE AND BRING A RETURN TO MORE TYPICAL
TRADES.  BY SUN-MON THE 00Z ECMWF/CMC AND GEFS/ECMWF MEANS ARE
MOST SIMILAR IN DEPICTING THIS IDEA WHILE THE LESS FAVORED 00Z/06Z
GFS HOLD ONTO A MORE PRONOUNCED INVERTED SURFACE TROUGH.

RAUSCH

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