Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
814 AM EDT Sat Aug 26 2017

Valid 00Z Sun Aug 27 2017 - 00Z Sun Sep 03 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 as ridging establishes itself northeast of Hawaii. This
will result in a broad mid/upper-level blocking pattern across the
north and central Pacific. A relatively weak tropical wave is
expected to pass south of Hawaii Sunday into Monday, which will
result in an increase in precipitable water values across the
state. The GFS continues to be slightly more aggressive with
spreading higher PWs across the Islands relative to the ECMWF,
although agreement has improved. The deepest moisture (PWs > 2
inches) should spread across the eastern islands late Sunday into
Monday. Thus, expect the potential for an increase in shower
activity during this time.

In the wake of this tropical wave, easterlies should increase a
bit (to near 20 kt), as the ridge builds northeast of Hawaii
through midweek. Dry air advecting from the subtropical ridge
Northeast of Hawaii will once again lower PWs and likely result in
drier than average conditions. By late next week, the digging
trough across the north central Pacific will push a cold front
southeastward, remaining well northwest of Hawaii through
Saturday. The ECMWF is now much weaker with the front and a wave
along it relative to yesterday (similar to the GFS), which should
keep east-northeasterly low-level flow in place across Hawaii,
resulting in relatively dry conditions through the end of next
week.

Ryan