Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Thu Feb 27 2020

Valid 00Z Fri Feb 28 2020 - 00Z Fri Mar 06 2020

...Heavy rain possible this weekend into next week...

Troughing to the northeast of the area will eventually form a
closed low that will move westward across the islands late
Sat-Mon. It will then weaken as it moves northwestward and
northward around an upper high to its northeast then east. The 00Z
models were in good agreement with this evolution but still vary
on the QPF placement and amounts. At the surface, models show a
1040-1043mb high settling near 38N/150W Sat/Sun then drifting
slowly to the east Mon-Wed. The pressure gradient of ~20mb over
~1000mi will yield breezy trades especially Friday through Monday
or Tuesday. By next Tuesday into Wednesday, heights will rise back
above average over the state. Prefer a blended solution between
the 00Z GFS/ECMWF given their similar evolution but still
different QPF solutions.

Upper low will bring cold/unstable airmass through the region with
500mb temps down to around -17C per the 00Z GFS/ECMWF/Canadian and
freezing levels near 9500ft/700mb. This would support some
convection in addition to potentially heavy snow on at least Mauna
Kea/Mauna Loa and Haleakala on Maui. Several inches of rain are
possible as the upper low passes through, but the heaviest
precipitation could stay just offshore to the east. With the
potential for deep tropical moisture to get pulled over the area,
the heavy rain threat remains. Highest probabilities of heavier
rain lie over the Big Island. By next Wednesday, with the upper
low likely disintegrated and heights on the rise, rainfall amounts
and coverage should decrease, continuing into Thursday.


Fracasso