Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
807 AM EDT Thu Aug 24 2017

Valid 00Z Fri Aug 25 2017 - 00Z Fri Sep 01 2017

Surface high pressure north of the state is forecast to all
guidance to gradually weaken over the next few days as a broad
area of negative height anomalies develops across the north
central Pacific. By the middle of next week, models show general
agreement that some degree of ridging will reestablish itself
northeast of the Hawaiian Islands, resulting in a broad
mid/upper-level blocking pattern across the north and central
Pacific. The weakening surface high north of the Islands should
result in a slight weakening of the trades through early next
week. A relatively dry air mass advect across Hawaii initially,
with precipitable water values decreasing into the 1.00-1.30 inch
range, which should suppress shower activity somewhat. A tropical
wave is expected to pass south of Hawaii Monday into Tuesday (a
bit slower than the progression shown by model guidance this time
yesterday), which could result in a moisture increase primarily
for the Big Island (PWATS increasing to 1.7-2.00 inches per the
00z ECMWF, slightly less per the 06z GFS). Thus, expect the
potential for an increase in shower activity across the Big Island
by early next week. In the wake of this tropical wave, easterlies
should pick up a bit, as the ridge reestablishes itself northeast
of Hawaii through midweek.

Ryan