Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
819 AM EDT Tue Mar 13 2018

Valid 00Z Wed Mar 14 2018 - 00Z Wed Mar 21 2018

...A heavy rain threat this week...

High pressure bridges to the north of the islands over the next
few days. Strong trades moderate midweek with low pressure
approach, but should rebuild later week with reinforcing high
pressure in the wake of the low.

The low develops west-southwest of Hawai'i as mid-level energy
lifts slowly toward the state as supported by satellite loops. A
preferred guidance composite advects deep moisture into the
islands with precipitable water values rising to over 2 inches (3+
standard deviations) as supported by blended imagery. This would
fuel a wet period through Friday with moderate to heavy rainfall
potential and local runoff issues. A winter weather advisory is
issued for Mauna Loa and Mauna Kea summits on the Big Island.

By Friday, a models/ensembles show another upper trough or closed
low near 25N/180 which should allow heights over Hawai'i to rise,
gradually lessening the heavy rain threat into the weekend.
Southeasterly trades persist through the weekend into early next
week with lingering scattered and windward terrain enhanced
showers as precipitable water values slowly decrease.

Looking forward, the slow translation of the mid-upper level
low/trough from the west may allow an associated frontal system
with renewed lead moisture inflow/height falls and convective
precipitation potential reach the western islands in about a week.
Guidance is varied with amplitude, but is decently clustered with
overall depiction of this feature, bolstering confidence.

Schichtel