Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
823 AM EDT Sun Apr 30 2017

Valid 00Z Mon May 01 2017 - 00Z Mon May 08 2017

...Heavy rainfall to continue for portions of Hawai'i...

The anomalous upper low will continue to slip southward through
Kauai/Niihau and settle southwest of the island chain by Tuesday
while filling. The surface front associated with the upper low
will remain mostly stationary over Maui or into the Big Island
today before retreating back to the west as the upper low sinks
southward. This surface boundary has acted as the main focus of
heavy rainfall this weekend so the focus will continue to be over
Maui and the Big Island on Sunday and then through Lanai/Molokai
on Monday. Precipitable water anomalies in the +2 to +4 sigma
range will support locally heavy rainfall of several inches in
favored areas. This moisture axis will eventually push back into
Oahu and then Kauai on Tuesday. By about Wednesday deep enough
easterly flow at lower levels will bring in lower PW air and help
decrease the rain coverage/intensity. As the upper low weakens
into an open wave and eventually remnant vorticity, upper ridging
will push in from the west to the north of the state. This has
been best advertised by the ECMWF but the global models and
ensembles now show much better agreement (though the
ECMWF/Canadian remain a bit stronger). This upper high should
slowly move to the northeast of the state next weekend, favoring a
much drier pattern for the 50th state. The 00Z NAEFS represents a
reasonable solution for next Fri-Sun.


Fracasso