Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
815 AM EDT Sat Aug 25 2018

Valid 00Z Sun Aug 26 2018 - 00Z Sun Sep 02 2018

...Tropical cyclone Lane expected to continue weakening and move
westward but maintain heavy rain/high wind threat into early next
week...

As of the 0900 UTC advisory from the Central Pacific Hurricane
Center, Lane has weakened to a tropical storm and should soon
begin tracking generally westward near 20N latitude over the next
couple days.  This will occur as the weakening system becomes
increasingly influenced by flow around strong surface high
pressure covering much of the eastern half of the Pacific. 
Although Lane's center of circulation will start moving away from
the main Hawaiian Islands, models agree that an axis of high
precipitable water values will persist over the state into the
first part of next week--supporting a continued threat of heavy
rainfall and flooding.  Some rain bands may contain strong and
gusty winds as well.

Around midweek upper ridging will begin to build north-south over
and then west of 160W longitude while a retrograding upper low
enters the picture to the northeast of the state.  The northerly
flow aloft will pull down drier air with precipitable water values
likely decreasing to below normal levels by late in the week. 
Thus from about Wednesday onward expect most rainfall to be light
and scattered with best focus over windward locales given
persistence of at least moderate trades.  From late week into next
weekend the primary model discrepancy involves the upper low to
the northeast of the state (possibly reaching a position north of
the state by Saturday) and associated surface reflection.  The 00Z
ECMWF pulls the upper low somewhat west and then northwest of
remaining guidance while developing a much stronger surface
reflection than other solutions--weakening trades more than the
consensus that includes the ECMWF mean.  Thus would recommend an
average of non-00Z ECMWF guidance for that part of the forecast.

Rausch