Prognostic Meteorological Discussion
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000
FXHW01 KWNH 161234
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
833 AM EDT MON OCT 16 2017

VALID 00Z TUE OCT 17 2017 - 00Z TUE OCT 24 2017

MODELS AND ENSEMBLES SHOW GENERALLY GOOD AGREEMENT ON THE LARGE
SCALE PATTERN ACROSS THE CENTRAL PACIFIC THROUGH THE NEXT WEEK.
UPPER RIDGE INITIALLY NORTHWEST OF HAWAII WILL MOVE A BIT EAST
OVER THE ISLANDS AS IT GRADUALLY WEAKENS. MEANWHILE, AN UPPER LOW
WELL NORTHEAST OF THE STATE WILL ALSO SLOWLY WEAKEN OVER THE NEXT
WEEK, HAVING VERY LITTLE IN THE WAY OF SENSIBLE WEATHER IMPACTS
OVER HAWAII. LOW-LEVEL EAST-NORTHEASTERLY FLOW OF 15-25 KT WILL
PERSIST ACROSS THE ISLANDS THROUGH MOST OF THE NEXT WEEK, AS A
SURFACE HIGH REMAINS ANCHORED NORTH OF THE STATE. A RELATIVELY DRY
AIR MASS WILL KEEP SHOWER ACTIVITY LIMITED TO THE FAVORED WINDWARD
TERRAIN AREAS THROUGH MOST OF THE WEEK. THE PATTERN ACROSS THE
CENTRAL PACIFIC SHOULD BEGIN TO CHANGE BY LATE NEXT WEEKEND AS
MOST MODELS AND ENSEMBLES SHOW A SHORTWAVE AMPLIFYING ACROSS THE
NORTH CENTRAL PACIFIC, WHICH COULD PUSH A COLD FRONT SOUTHWARD IN
THE GENERAL DIRECTION OF HAWAII. THERE IS A FAIRLY LARGE DEGREE OF
SPREAD, HOWEVER, AS TO THE EXACT EVOLUTION OF THE TROUGH, AND
WHETHER A MORE FULL LATITUDE TROUGH AMPLIFIES NORTH OF HAWAII (AS
SHOWN BY THE GFS AS WELL AS THE GEFS/NAEFS/CMC ENSEMBLES) OR
WHETHER A SOMEWHAT WEAKER WAVE MOVES EAST MORE QUICKLY (AS SHOWN
BY THE CMC). THE 00Z ECMWF WAS GENERALLY IN THE MIDDLE OF THESE
TWO EXTREMES. THE EXACT EVOLUTION OF THIS TROUGH WILL HAVE A
SIGNIFICANT IMPACT ON THE ORIENTATION OF THE SURFACE COLD FRONT
AND HOW MUCH MOISTURE GETS DRAWN NORTHWARD INTO IT. NONETHELESS,
THERE SHOULD BE SOME TYPE OF WAVE AMPLIFYING NORTH OF HAWAII BY
LATE IN THE WEEKEND, WHICH COULD PUSH A FRONT TOWARD THE ISLANDS,
BUT IT REMAINS UNCLEAR ON HOW QUICKLY THE FRONT WILL MOVE SOUTH
TOWARD THE ISLANDS AND HOW MUCH PRECIPITATION COULD RESULT ACROSS
HAWAII DURING THIS FORECAST PERIOD.

RYAN

$$





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