Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
806 AM EDT Mon Jun 24 2019

Valid 00Z Tue Jun 25 2019 - 00Z Tue Jul 02 2019

A deep upper-level low (-3 standard deviations at 500 hPa) and
associated surface front are situated several hundred miles
northwest of Hawaii early this morning, and are expected to slowly
migrate eastward toward Hawaii over the next couple days. Model
consensus is now relatively good with respect to this feature, and
a general model blend should sufficiently represent the expected
evolution. Relatively high PWs (well over 2 inches) and with some
enhanced instability associated with the upper low will support
areas of deep convection with heavy rainfall, especially for the
western islands. ECENS and GEFS ensemble probabilities have
gradually increased with respect to the heavy rainfall potential
across Kauai, Niihau, and perhaps Oahu peaking from Tue into Wed,
with some potential for localized rainfall amounts of 3-4 inches.
Flash flooding will be a possibility for some areas. Additionally,
the approach of this system will likely disrupt the trades, a
period of southeasterly or southerly flow at the lower levels
likely through Wed. By late in the week, a return to more typical
conditions appears likely as models/ensembles continue to show
good consensus that the upper trough will lift out as upper
ridging builds overhead, allowing moderate trades and more typical
windward showers to resume.

Ryan