Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Mon Mar 16 2020

Valid 00Z Tue Mar 17 2020 - 00Z Tue Mar 24 2020

...Heavy rainfall threat especially during the first half of the
week...

Guidance is fairly consistent in showing a deep and concentrated
upper low settling to the west of the main islands early this week
and remaining in place through about Wednesday night.  Then the
low should track northward and quickly open up under the influence
of a trough/upper low farther to the northwest.  In association
with this Kona low the model/ensemble consensus maintains the
threat for heavy rainfall/flash flooding concerns over the state
with deep layer southerly flow pulling up sufficient moisture to
yield precipitable water values exceeding three standard
deviations above normal for a period of time.  Adjustment in the
00Z GFS has led to better agreement regarding highest rainfall
potential over the western islands.  However there is a decent
cluster of model/ensemble mean guidance suggesting that the axis
of highest moisture may drift from west to east across the
western-central islands during the first half of the week before
returning to the west.  Thus potential remains for some of the
enhanced rainfall/thunderstorm activity to reach farther eastward
than suggested by explicit QPF output.  Also the global model
guidance tends to have difficulty in resolving smaller-scale
convective rainfall.  Even though the Kona storm lifts northward
later in the week there may be a lingering band of shortwave
energy and deep moisture that could promote some additional
rainfall over or close to the western islands. 

Expect brisk to strong southeasterly winds during the first half
of the week within the tight gradient between the Kona low and
high pressure to the east.  Southeasterly winds should continue
into the early weekend, followed by a more typical easterly trade
pattern by next Sunday-Monday.  The easterly low-level flow will
bring in drier air and lighter showers with windward/mountain
focus.

Rausch