Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
822 AM EDT Sat Jun 22 2019

Valid 00Z Sun Jun 23 2019 - 00Z Sun Jun 30 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 remain northwest of the state through
the weekend. This along with surface high pressure well northeast
of the state will keep relatively light trades (10-20 kt) in place
into early next week. Models/ensembles show general consensus that
this feature should very slowly migrate eastward toward Hawaii by
Tue-Wed, and spread has reduced compared to yesterday as to the
extent which heights may fall across the state. The majority of
deterministic solutions now keep the lowest heights just northwest
of Hawaii, an idea which is supported by ensemble means. Models do
agree that moisture should increase, with PWs in both the ECMWF
and the GFS now over 2 inches by Tue. This should support areas of
heavy rainfall, especially for the western islands. ECENS and GEFS
ensemble probabilities have also come into much better agreement
relative to yesterday, with both now showing potential for heavy
rainfall (1-2 inches with localized higher amounts) across Kauai
and Niihau from late Tue into Wed. 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 later next week, a return to more typical
conditions appears likely as models/ensemble 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