Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
701 AM EST Tue Mar 06 2018

Valid 00Z Wed Mar 07 2018 - 00Z Wed Mar 14 2018

A weak cold front moving southward through the area today is
expected to stall out tonight near the Big Island as short wave
energy dives into and elongates the positively-tilted trough north
of the state.  Moisture and instability along the boundary is not
too impressive, so expect mostly scattered windward showers to
persist through Thursday.  Farther north behind the front, dry and
slightly cooler air will push across most of the island chain,
keeping any shower activity isolated and light.  During Friday, an
amplifying polar stream system will kick out the elongated trough
and allow the front to pass fully south of all islands.  High
pressure building in from the northwest will maintain mostly dry
conditions at least through the weekend, though trades will be on
the brisk side and gradually shift from a northeasterly to more
easterly direction by the end of the weekend.

The main forecast problem arises late in the period.  The models
all generally show the upper low currently just west of the
dateline and north of 30N drifting southward into the subtropical
stream over the next few days, then pushing eastward toward the
state early next week.  The main differences among the models is
timing...with the GFS quickest advancing it eastward (and also
overall the strongest solution), while the ECMWF is slowest.  At
this time, the Canadian and NAVGEM are leaning toward the faster
solution, so based on model consensus, would tend to discount the
slower ECMWF (and its ensembles) at this time.  As this system
approaches, it will lift abundant tropical moisture across the
state from southwest to northeast Monday-Tuesday.  Widespread
showers are likely across much of the state by Tuesday,
potentially focusing over the northern islands along a weak front
extending westward from a system approaching the mainland.

Klein