Prognostic Meteorological Discussion
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000
FXHW01 KWNH 251228
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
827 AM EDT MON SEP 25 2017

VALID 00Z TUE SEP 26 2017 - 00Z TUE OCT 03 2017

TO COMMENCE THE FORECAST PERIOD, A CLOSED UPPER LOW WILL BE
SPINNING ALONG 150W LONGITUDE, JUST EAST OF THE HAWAI`IAN ISLAND
CHAIN. WHILE INITIALLY DRIFTING FARTHER EAST IN TIME, THERE ARE
SUGGESTIONS THE CIRCULATION COULD SWING BACK TOWARD THE WEST. THE
SOLUTIONS ARE QUITE VARIABLE SUGGESTING LOW CONFIDENCE IN EVENTUAL
PLACEMENT. IN ADDITION TO THIS FEATURE, A MUCH MORE ROBUST CLOSED
LOW IS EXPECTED TO DETACH FROM THE PREVAILING WESTERLIES DURING
THE UPCOMING WEEKEND WITH A POSITION ALONG OR JUST EAST OF THE
INTERNATIONAL DATELINE. BY SUNDAY AFTERNOON, THE 06Z GFS/00Z ECMWF
ARE LITERALLY 10 DEGREES APART IN LONGITUDE FROM ONE ANOTHER WITH
EVEN MORE SCATTER AMONG THEIR INDIVIDUAL ENSEMBLE MEMBERS.
HOWEVER, THERE IS AGREEMENT IN SHIFTING THIS NEGATIVE HEIGHT
ANOMALY WESTWARD, AWAY FROM THE REGION, MOVING INTO EARLY NEXT
WEEK.

AT THE SURFACE, GIVEN AN INITIALLY WEAK PRESSURE GRADIENT ACROSS
THE CENTRAL PACIFIC, EAST-NORTHEASTERLY WINDS AROUND 10 TO
OCCASIONALLY 15 KNOTS IS EXPECTED THROUGH MUCH OF THE WEEK. BY
FRIDAY INTO THE WEEKEND, WARM ADVECTION IN ADVANCE OF THE NEXT
SYSTEM DROPPING SOUTHWARD SHOULD LEAD TO A MORE SOUTHEASTERLY FLOW
REGIME. AS THIS PARTICULAR FEATURE BEGINS TO RETROGRADE,
OPERATIONAL/ENSEMBLE GUIDANCE AGREE ON BUILDING A STRONG SURFACE
ANTICYCLONE NORTH OF HAWAI`I BY SUNDAY ONWARD LEADING TO
STRENGTHENING TRADES. REGARDING PRECIPITATION, WINDWARD SHOWERS
WILL BE THE NORM WITH A POTENTIAL UPTICK IN COVERAGE BY MID-WEEK
AS A SLUG OF HIGHER PRECIPITABLE WATERS VALUES SWINGS WESTWARD
THROUGH THE REGION. ANY RAINFALL WITH THE FRONTAL ZONE DESCENDING
FROM THE MID-LATITUDES SHOULD REMAIN WELL WEST OF HAWAI`I. AND
GIVEN THE PRESENCE OF THE UPPER LOW LINGERING TO THE EAST, SOME
ADDITIONAL SHOWERS MAY SPAWN.


RUBIN-OSTER


$$




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