Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
744 AM EDT Sun Sep 14 2014
Valid 00Z Mon Sep 15 2014 - 00Z Mon Sep 22 2014
The 14/00Z GFS/ECMWF deterministic runs were very reasonable
pieces of guidance into day 5 (19/12Z) with several of the key
features for Hawai'i and the north central Pacific.
The forecast for the central Pacific remains essentially
unchanged---with the western portion of the Subtropical Ridge
rebuilding and migrating eastward to a position near 35N 160W.
The ridge then flattens---migrating east-southeastward to
approximately 33N 142W. The 'flatter' Subtropical Ridge axis
solution in the central Pacific along 30N-35N latitude results in
a brief return of the more typical 'Northeast Trades' from
Wednesday 'til the Friday/Saturday time frame when the flow in the
northeast Pacific begins to gain amplitude---the result of
mid-latitude energy from the southern Bering Sea transferring
downstream to the Gulf of Alaska by forecast period's end.
For Hawai'i, trades should be on the increase around Wednesday
with the positioning of the Subtropical Ridge axis northeast of
the Islands to give the ITCZ and cloud debris embedded within it a
chance to spread northward and northwestward over the
Islands---primarily between day 3 and day 5.
Recommend a 50/50 blend of the 14/00Z ECENS-GEFS--both handling
the flow pattern quite well over most of the western hemisphere.
Meanwhile, thought the deterministic GFS/ECMWF appeared to add
some value in the central and northern Pacific until Friday.