Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
808 AM EDT Mon Aug 22 2016

Valid 00Z Tue Aug 23 2016 - 00Z Tue Aug 30 2016

Models and ensembles continue to show similar ideas for most
aspects of the forecast covering the next seven days.  Trades will
vary depending on strength and proximity of eastern Pacific high
pressure.  Winds will likely be weakest early this week and then
strengthen into Thursday as the surface high retrogrades and
becomes stronger.  The high will keep retrograding for a while but
also weaken so trades should weaken slightly late week into the
weekend before stabilizing Sunday-Monday.

ECMWF trends over the past couple days have brought it into line
with the GFS regarding the axis of high precipitable water values
extending across the islands during the first half of the week. 
There are still differences in magnitude with the 00Z ECMWF
showing a larger area of 2-2.25 inch PWATs which lead to max
standardized anomalies in the plus 4-5 range compared to plus
3-3.5 or 4 centered mainly over the Big Island in the 00z GFS/GEFS
mean.  The combination of available deep moisture, a modest
weakness aloft through Tuesday, as well as potential sea breeze
boundaries allowed by relatively weak trade flow, may promote some
areas of heavy rainfall through at least Tuesday.  Activity should
begin trending somewhat lighter/less organized Wednesday as the
axis of deep moisture begins to track westward and heights aloft
rise.  From Thursday onward expect a drier pattern with greater
windward focus for any showers that occur.  Ridge aloft should be
strongest late in the week with gradual weakening Saturday-Monday.

Rausch