Prognostic Meteorological Discussion
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FXHW01 KWNH 261212
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
811 AM EDT TUE SEP 26 2017

VALID 00Z WED SEP 27 2017 - 00Z WED OCT 04 2017

INTO LATE THIS WEEK EXPECT TRADES TO BECOME A LITTLE MORE BRISK AS
THE SURFACE RIDGE TO THE NORTH OF THE STATE STRENGTHENS A BIT AND
AFTER A WEAKENING TROUGH INITIALLY JUST TO THE EAST PASSES OVER
THE ISLANDS.  WITHIN THIS FLOW REGIME SHOWERS WILL TEND TO FAVOR
WINDWARD TERRAIN, WITH THE PASSAGE OF THE SURFACE TROUGH POSSIBLY
BRINGING A BRIEF ENHANCEMENT OF ACTIVITY.

AFTER FRIDAY THE FOCUS OF THE FORECAST TURNS TO A POTENTIAL
INTERACTION OF BERING SEA ENERGY AND A CENTRAL PACIFIC
TROUGH/UPPER LOW.  MOST OPERATIONAL MODELS END UP CLOSING OFF A
FARTHER SOUTH UPPER LOW NEAR 30N LATITUDE BY AROUND MONDAY BUT
WITH WIDE SPREAD ON LONGITUDE.  THE 00Z GFS (AND UKMET THROUGH 00Z
MONDAY) ARE FARTHEST EAST AND 00Z ECMWF/CMC ARE ABOUT TEN DEGREES
FARTHER WEST.  THE FULL RANGE OF 00Z GEFS/ECMWF/CMC ENSEMBLES IS
EVEN BROADER, SPANNING GREATER THAN 20 DEGREES LONGITUDE.  THE 00Z
GFS IS AT LEAST 3/4 TOWARD THE EAST SIDE OF THE ENVELOPE WITH THE
00Z GEFS MEAN CLOSE TO THE 06Z GFS WHICH IS A FEW DEGREES FARTHER
WEST.  00Z ECMWF ENSEMBLES SPAN NEARLY THE ENTIRE ENVELOPE BUT
WITH A HIGHER PROPORTION CLOSER TO THE WESTWARD OPERATIONAL RUN.
WITH CMC ENSEMBLES TENDING TO LEAN WESTWARD AS WELL, THE MORE
LIKELY SCENARIO CURRENTLY APPEARS TO LIE IN THE WESTERN HALF OF
THE SPREAD.  ASSUMING SUCH A SOLUTION, THE LEADING SURFACE FRONT
AND ASSOCIATED HEAVIER RAINFALL WOULD REMAIN FARTHER NORTHWEST OF
THE ISLANDS RELATIVE TO THE 00Z/06Z GFS RUNS.  WINDS SHOULD TURN
MORE SOUTHEASTERLY DURING THE WEEKEND AND EARLY NEXT WEEK WITH A
CONTINUATION OF SCATTERED SHOWERS.

RAUSCH

$$





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