Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Wed May 11 2022

Valid 00Z Thu May 12 2022 - 00Z Thu May 19 2022

Latest models and ensemble means agree on a gradual but ultimately
significant pattern change taking place between now and the middle
of next week.  From today into the weekend, expect gradual
weakening of eastern Pacific high pressure and somewhat lighter
trades by the weekend versus initially brisk strength.  Near to
somewhat below normal precipitable water values along with upper
ridging overhead should keep the primarily windward-focused
showers on the light side.  At some point during the weekend and
early next week the background flow may become light enough to
allow for sea/land breeze influence on shower activity at some
locations.  Meanwhile an evolving wavy front to the distant
northwest may alter the pattern enough to turn winds more
southeasterly.  During the early to middle part of next week, an
upper trough/low (part of a Bering Sea through central Pacific Rex
block pattern) should approach from the northwest.  The
combination of the leading cold front and modest strengthening of
the East Pacific high may tighten the surface gradient and further
adjust the pattern, potentially yielding stronger and more
southerly winds by next Wednesday.  Guidance agrees upon
increasing moisture as this evolution occurs, just with
differences to what extent.  At the moment the GFS/GEFS mean
extend the upper trough somewhat farther southeast than other
guidance to result in a more aggressive increase of precipitable
water values.  This is an occasional bias of the GFS but at the
same time the current guidance spread is generally within typical
error ranges for forecasts 6-7 days out in time.  A compromise
halfway between the GFS/GEFS and ECMWF/ECMWF mean or tilted
slightly to the ECMWF cluster seems to be the most reasonable
option for this part of the forecast.

Rausch