Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
347 AM EDT Mon May 29 2023

Valid 00Z Tue May 30 2023 - 00Z Tue Jun 06 2023

Expect a typical trade pattern with windward/mountain focused
showers over the next seven days as high pressure initially a
little north of 40N latitude gradually trends weaker as it settles
along 30N latitude by next Sunday-Monday.  Wind speeds should
increase toward moderate or brisk levels by mid-late week and then
stabilize as the closer proximity of high pressure offsets its
weakening trend.  Guidance is consistent in showing an east-west
weakness aloft over or just north of the state helping to increase
moisture/rainfall somewhat through midweek, and allowing for the
possibility that a few showers could stray into leeward locales.

From late week into early next week, guidance continues to differ
significantly for how much moisture there will be over the
islands, with some dependence on subtle details (having low
predictability several days out in time) of a lingering weakness
over/west-southwest of the area.  Also a couple of shortwaves
should pass by to the north, and the far southern periphery of
these features may have some influence.  As has been the case
recently, the 00Z ECMWF continues to show a pronounced drier trend
Friday onward versus the GFS that keeps rather high precipitable
water values over the Big Island (while offering somewhat drier
conditions farther northwest).  In general the GEFS and ECMWF
means both continue to favor a compromise approach while just
moderately tilting toward the ideas of their respective parent
models.  A compromise among these means looks best for a single
deterministic forecast given the continued spread and uncertainty
for important details aloft.

Rausch