Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
722 AM EST Tue Feb 20 2018

Valid 00Z Wed Feb 21 2018 - 00Z Wed Feb 28 2018

Upper low to the north of the region will continue to lift
northward and weaken, allowing drier air to remain over Hawai'i.
Precipitable water values will generally be under 1.25 inches
through Wednesday. By Thursday, another upper low is forecast to
form to the northwest of the area (around 30N/170W or over the
Paphanaumokuakea Marine National Monument) with a downstream
narrow ridge along 150W. This will allow deep tropical moisture to
surge northward across the state with locally moderate to heavy
rain and embedded thunderstorms. Precipitable water values are
forecast to rise to between about 1 1/3 to 1 3/4 inches through
the period (next Tuesday) which is well above average for late
February. Ensembles indicate a reloading of the upper low near or
just west of the same location next week which may pull the
precipitable water axis westward next week, perhaps west of
Kauai/Ni'ihau. Latest 06Z GFS and 00Z ECMWF generally fall in line
within the ensemble spread, and a blend of these solutions should
suffice, though their QPF differences are much larger than their
500mb or surface patterns.


Fracasso