Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
817 AM EDT Thu Apr 09 2015

Valid 00Z Fri Apr 10 2015 - 00Z Fri Apr 17 2015

The 9/00Z forecast cycle was consistent with previous medium range
projections in the north Pacific, Alaska, Mainland west coast and
Hawai'i. On-going Hawai'i forecasts appeared to be in good order.

The 9/00z GEFS, ECENS, NAEFS ensemble means and their
deterministic runs maintain a rather persistent split-flow
solution for the Subtropics and Hawai'i this forecast period.
Mid-level and upper-level westerlies prevailing at low latitudes
(along 20N) and at high latitudes (50N) produce very little
amplitude to the pattern west of 140W. What amplitude that does
emerge---has room to develop in the far east Pacific---but this
has impacts for the Mainland and southern Alaska. 

Around day 4 (next Monday), the low-latitude westerlies begin to
shift northward (to 25N)---in response to an amplifying trough
invof the central Aleutians near 170W. The deterministic 9/00Z
GFS/ECMWF serve this scenario quite well, and either solution
could be used heading into next Tuesday.

Beyond Tuesday (day 5), interesting 250 mb flow regime attempting
to setup near 160W---and migrating eastward to 150W by the end of
this forecast period. Mid-latitude upper-trough and jet-level
winds digging southward along ~155W attempt a brief 'phasing'
sequence north of Hawai'i with the low-latitude 250mb jet axis. At
least, the GFS creates this wetter scenario for next Wednesday and
Thursday. The ECMWF keeps the streams separated---though its
southward progression of the mid-latitude upper-level trough and
digging high-latitude jet streak are similar to the GFS. With the
deterministic GFS/ECMWF forecast solutions in relatively-good
agreement across the mid-latitude Pacific and Subtropics---worth
watching the scenario unfold.

With this mind...recommend a blend of the 9/00Z GEFS and ECENS
beyond 16/00Z to handle the scenario offered by both deterministic
runs---and anticipate lower heights and the possibility of
enhanced convection along a mid-latitude cold front---north of
Hawai'i. The cold front itself may never drift south of 25N
latitude late in this forecast period---but convective outflow
could.

Vojtesak