Prognostic Meteorological Discussion
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FXHW01 KWNH 281225
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
824 AM EDT FRI APR 28 2017

VALID 00Z SAT APR 29 2017 - 00Z SAT MAY 06 2017

...HEAVY RAINFALL LIKELY FOR PORTIONS OF THE 50TH STATE...

A DEEP UPPER LOW IS FORECAST TO DROP JUST WEST OF DUE SOUTH ALONG
160W OVER THE NEXT FEW DAYS, MAINTAINING A TROPICAL MOISTURE PLUME
AXIS INTO THE CENTRAL/EASTERN ISLANDS THIS WEEKEND. THE RECENT
GFS/ECMWF/UKMET RUNS WERE CLOSELY ALIGNED (CANADIAN WAS DISPLACED
TO THE NORTHEAST). NEXT WEEK, THE UPPER LOW IS FORECAST TO SLOWLY
WEAKEN AND DRIFT SOUTHWESTWARD (PER ECMWF) OR WOBBLE EASTWARD JUST
SOUTH OF 20N (PER GFS) AS UPPER RIDGING BUILDS IN FROM THE WEST.
THE ECMWF AND ITS ENSEMBLES WERE MORE BULLISH WITH THE UPPER
RIDGING THAN THE GFS/GEFS. SINCE UPPER LOWS TEND TO HANG AROUND
LONGER THAN THE MODELS FORECAST (THIS ONE HAS LOW PREDICTABILITY
IN TRACK LATER NEXT WEEK) WOULD TEND TO FAVOR A SLOWER INCREASE IN
HEIGHTS UNTIL THE MODELS/ENSEMBLES HAVE A CLEARER CONSENSUS.

MODELS AND ENSEMBLES SHOW POTENTIAL FOR SIGNIFICANT RAINFALL
ACROSS THE REGION, ESPECIALLY OVER MAUI AND THE BIG ISLAND THIS
WEEKEND AND THEN SPREADING NORTHWESTWARD THEREAFTER. LOCATION OF
THE SURFACE FRONT/TROUGH WILL SERVE AS AN AMPLIFYING FOCUS FOR
RAINFALL. GEFS M-CLIMATE QPF VALUES LIE ABOVE THE 99TH PERCENTILE
(24-HR AMOUNTS THIS WEEKEND INTO NEXT WEEK) WITH AN AREA OF `MAX`
VALUES THIS WEEKEND INTO MONDAY AROUND MAUI/LANAI/MOLOKAI.

FRACASSO


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