Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Sun Jun 23 2019

Valid 00Z Mon Jun 24 2019 - 00Z Mon Jul 01 2019

A deep upper-level low (-4 standard deviations at 500 hPa) is
situated several hundred miles northwest of Hawaii early this
morning, and is expected to slowly migrate eastward toward Hawaii
by Tue-Wed. Satellite/radar this morning show areas of deeper
moisture and convection already occurring just west of Kauai.
Model consensus with respect to this feature has continued to
improve over recent days, and a general model blend should
sufficiently represent the expected evolution. Relatively high PWs
(>2 inches) as soon as Sunday night should support areas of heavy
rainfall, especially for the western islands. ECENS and GEFS
ensemble probabilities both show the potential for heavy rainfall
across Kauai and Niihau from late Tue into Wed, with some guidance
suggesting the potential for localized rainfall amounts exceeding
3 inches. Additionally, the approach of this system will likely
disrupt the trades, with the potential for a period of
southeasterly or southerly flow at the lower levels 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