HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
802 AM EDT SUN MAY 12 2013

VALID 00Z MON MAY 13 2013 - 00Z MON MAY 20 2013

EXPANSIVE UPPER-LEVEL RIDGE IN THE TROPICAL SOUTHWEST PACIFIC
CONTINUES TO STRENGTHEN AND EXTEND  EASTWARD TO WAKE/MIDWAY
ISLANDS THROUGH MIDWEEK. HAWAI'I WILL EXPERIENCE MODERATE
TRADES...SLIGHTLY ABOVE NORMAL TEMPERATURES AND SEASONAL RAINFALL
DISTRIBUTIONS UNDER THE INFLUENCE OF THIS FEATURE.

NEXT FRI/SAT (DAY 5-6)...THE FLOW PATTERN BEGINS A SUBTLE
TRANSITION PERIOD ACROSS THE NORTHERN PACIFIC...AS A DEEP VORTEX
AT HIGH LATITUDES SHIFTS AWAY FROM ALASKA AND THE BERING SEA AND A
SPLIT-FLOW SCENARIO BRIEFLY DEVELOPS NORTH OF 50N.

THE 12/00Z CANADIAN/GFS AND ECMWF DETERMINISTIC/ENSEMBLE GUIDANCE
IN FAIRLY DECENT AGREEMENT WITH THE MID-LATITUDE WAVE DEVELOPMENT
AND PROGRESSION ACROSS THE NORTHERN PACIFIC. 12/00Z ECMWF/GFS
DETERMINISTIC FORECASTS TRACK A H5 CUTOFF LOW THROUGH THE SW GULF
OF ALASKA NEXT WEEKEND...WHILE THE 12/00Z CANADIAN CARRIES MORE OF
AN OPEN WAVE SOLUTION. HOWEVER...ALL THREE ATTEMPT TO PHASE ENERGY
TO SOME DEGREE NORTHWEST OF THE SYSTEM (INVOF OF THE CENTRAL
ALEUTIANS) BEFORE THE DEEP VORTEX LIFTS NORTHWARD OUT OF THE
BERING STRAIT.

THE IMPLICATIONS OF PHASING--A FEATURE OF THIS UNUSUAL SPRING FLOW
PATTERN IN THE PACIFIC-- INDIRECTLY IMPACTS HAWAI'I NEXT WEEKEND.
AND FOR THE MOST PART...

IF THE 12/00Z GFS/ECMWF DETERMINISTIC FORECASTS VERIFY...THERE
WILL BE YET ANOTHER LATE-SPRING FRONT CROSSING 160W...AND
APPROACHING HAWAI'I (KAUAI) FROM THE NORTHWEST ON SATURDAY
(18/18Z). THE 12/00Z GEFS/EC ENSEMBLES MEANS SUPPORT SUCH A
SCENARIO WITH A BROAD UPPER-LEVEL TROUGH AND UNSETTLED WEATHER
RETURNING TO THE ISLANDS SUNDAY (DAY 7) BUT ARE LESS AGGRESSIVE
WITH THE DEVELOPMENT OF A DEEP H5 CUTOFF.

TO HANDLE THE UNCERTAINTY IN THE LATTER PART OF THE
EXTENDED...BLENDING THE 12/00Z GEFS/EC ENSEMBLE MEANS...WOULD
TEMPER THE EFFECTS OF THE MID-LATITUDE FRONT AND DEEP CLOSED LOW
SOLUTION FOR THE ISLANDS. 

VOJTESAK