Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
332 AM EDT Thu Mar 12 2020

Valid 00Z Fri Mar 13 2020 - 00Z Fri Mar 20 2020

A cold front is forecast to stall across the western Hawaiian
islands today, and drift very slowly southeastward across the
state through late this week, eventually washing out over the
weekend. Moisture associated with the boundary is expected to
initially be limited (PWs near 1 inch), keeping shower activity
somewhat sparse through Thursday. As the front weakens over the
weekend, deeper moisture is forecast to nonetheless spread north
toward Hawaii ahead of an amplifying upper-level trough northwest
of the state. This should bring an increase in convection across
Hawaii through the weekend, with relatively light and variable
flow in the vicinity of the weakening making showers a possibility
for typical windward as well as mauka locations. By Mon-Tue,
models show improved consensus that a Kona Low should develop west
of Hawaii. The Kona Low will increase advection of deep moisture
across Hawaii, increasing the potential for heavy rainfall next
week. ECENS and GEFS ensemble probabilities show potential for
heavy rainfall, especially across the western islands next
Mon-Tue, possibly shifting east across the remaining islands
through midweek (although the latter is a bit more uncertain).
Heavy rains could be sufficient to produce flash flooding for some
areas next week. Deterministic solutions suggest the potential for
multi-inch rainfall totals, although confidence is low on the
specific placement of the heaviest amounts. Additional impacts of
the low will include strong southerly flow expected to develop
across the western islands Mon-Tue, with wind gusts of in excess
of 40 mph possible.

Ryan