Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
822 AM EDT Wed Mar 14 2018

Valid 00Z Thu Mar 15 2018 - 00Z Thu Mar 22 2018

...Heavy rain threat...

Potent high pressure is bridging to the north of the islands.
Strong trades moderate Thursday as the high shifts to the eastern
Pacific and surface low pressure/mid-level trough energies lift
northeastward toward the state. Deep moisture is feeding into the
islands with precipitable water values to rise over 2 inches (3+
standard deviations). This is supported by a favored guidance
composite and satellite/blended loops. This should fuel a wet
period through Friday with potential for moderate to heavy
rainfall and local runoff issues. A winter weather advisory
remains in effect 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 over 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, a slow translation of the mid-upper level
low/trough and deepening surface low from the west may allow an
associated frontal system with renewed lead moisture inflow/height
falls and convective precipitation potential reach the islands
Tuesday into next Wednesday. Guidance is varied with amplitude,
but remains decently clustered with overall depiction of this
feature, bolstering confidence.

Schichtel