Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
812 AM EDT Sat Apr 29 2017

Valid 00Z Sun Apr 30 2017 - 00Z Sun May 07 2017

...Heavy rainfall likely for portions of the 50th state...

A deep upper low will drop just west of due south along 160W over
the next few days, maintaining a tropical moisture plume axis into
the central/eastern islands through early next week. The recent
deterministic model runs were mostly aligned and all show the
surface boundary lingering near Maui and the Big Island this
weekend. Next week, the upper low is forecast to slowly weaken to
the southwestward of the state as upper ridging builds in from the
west. The ECMWF/Canadian and their ensembles remain more bullish
with the upper ridging than the GFS/GEFS. Would tend to favor a
slower rather than quicker increase in heights given how deep the
upper low is initially but amplified pattern over the Pacific may
support the ECMWF-led solution. The 00Z NAEFS provides a nice
middle ground solution.

Models and ensembles show potential for significant rainfall
across the region, especially over Maui and the Big Island over
the next couple of days and then spreading northwestward
thereafter as the upper low and surface boundary weaken. GEFS
M-Climate QPF values still lie above the 99th percentile (24-hr
amounts this weekend into next week) with an area of 'MAX' values
around Maui/Lanai/Molokai, which lines up with the hi-res models
over the next 48 hrs (aided by convection as well). Higher
elevations will see snowfall thanks to very cold upper level
temperatures (500mb temps show 'MIN' values per the NAEFS on
Sunday relative to the 30-yr reanalysis period of the CFSR).

Fracasso