Prognostic Meteorological Discussion
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FXHW01 KWNH 161316

Hawaii Extended Forecast Discussion...Corrected
NWS Weather Prediction Center College Park MD
915 AM EDT Fri Mar 16 2018

Valid 00Z Sat Mar 17 2018 - 00Z Sat Mar 24 2018

...The current heavy rain threat eases by Saturday...
...Another heavy rain/flash flood threat late Tuesday into next

Trades re-establish today as moisture slowly fades as the system
responsible to the heavy rainfall yesterday lifts north and
northeast of the Islands.  Windward showers/thunderstorms are
likely to be more active than usual today with heavier rain than
typical trades due to lingering moisture and a weaker wind regime,
with more typical windward showers likely Saturday into Monday or
Tuesday as the trades attempt to recapture their usual vigor.  The
departing system digs down to the northeast of the archipelago
which should keep trades in the offing for the main islands into

However, a new system moves slowly in from the
west/Papahanaumokuakea Marine National Monument which breaks down
the trades and reintroduces heavy rain into the main Hawai`ian
islands from roughly Tuesday night/Wednesday into next Friday.
Precipitable water values are forecast to rise into the 1.75-2"
ballpark, which even in flat/non-Hawai`ian terrain would lead to
the possibility of 2.5" an hour rain rates -- any cell mergers
would double the potential.  The guidance is very agreeable
regarding progression of the next system, though the 00z ECMWF is
likely too strong/too far northwest in its surface low placement
with its depiction of this system.  Considering saturated
conditions from recent rainfall and the rugged topography, flash
flooding is a realistic hazard during this time frame.


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