Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
819 AM EDT Sun Aug 27 2017

Valid 00Z Mon Aug 28 2017 - 00Z Mon Sep 04 2017

A broad area of negative height anomalies is forecast by all
guidance to develop across the north central Pacific over the next
few days, and amplify by next weekend, as ridging establishes
itself northeast of Hawaii. This will result in a broad
mid/upper-level blocking pattern across the Pacific north of
Hawaii. A relatively weak tropical wave is expected to pass south
of Hawaii today, which will result in an increase in shower
activity across the eastern islands persisting into Monday.

In the wake of this tropical wave, easterlies should increase a
bit (to near 20 kt), as the ridge builds northeast of Hawaii. Dry
air advecting from the subtropical ridge Northeast of Hawaii will
lower PWs substantially by mid week (to near 1"), and likely
result in drier than average conditions. By late in the week, the
digging trough across the north central Pacific will push a cold
front southeastward, remaining well northwest of Hawaii through
Sunday. The ECMWF and GFS are in general agreement on the timing
of the front and the moisture plume associated with it. The front
may begin to impact low-level wind profiles by Sunday, with both
the GFS and ECMWF showing low-level winds veering to more
southerly. While this should eventually increase moisture across
the islands, both models keep generally low PWs across Hawaii
through next weekend.

Ryan