Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Mon Feb 13 2023

Valid 00Z Tue Feb 14 2023 - 00Z Tue Feb 21 2023

Guidance continues to show an active pattern this week into the
weekend, with some areas of heavy rainfall possible through
midweek and then potential for a more significant heavy rainfall
threat in the Thursday-Saturday period.  Consensus still depicts
an upper low over/just east of the main islands from now through
Tuesday night, followed by a shift to the west/southwest of the
state Wednesday-Thursday as shortwave energy to the west combines
with the initial upper low and an upper ridge tracks by to the
north.  The upper low may linger in place for a day or so before
dropping southward during the weekend into early next week.  Most
guidance suggests that the upper low position during
Thursday-Saturday will be the most favorable for bringing in
abundant moisture from the southeast, with southeast-facing areas
of the Big Island seeing the heaviest rainfall.  There is still
uncertainty over what becomes of the moisture axis from Saturday
onward in light of relative differences in strength of the upper
low and ridge to the north/northeast.

Expect brisk easterly trades to focus rainfall over
windward/mountain areas early in the week, with models/means
indicating a band of somewhat greater moisture rotating into the
central/northwestern islands by Tuesday-Wednesday.  Guidance still
depicts a surface trough with embedded wave crossing the state
from east to west around midweek.  There has been some convergence
for timing of this feature relative to 24 hours ago, with the
GFS/CMC nudging a bit faster toward the ECMWF.  There is still
about 12 hours of timing spread though.  The approach and passage
of this trough will alter the distribution of precipitation.  From
late week onward, guidance preference continues to lean toward an
average of non-GFS guidance like yesterday.  The GFS has tempered
its upper low depth somewhat compared to yesterday but is still a
bit on the strong side (and correspondingly weaker with the
southwestern extent of upper ridging to the northeast).  The GFS
also continues to be more aggressive to develop one or more
compact surface lows tracking within the southeasterly flow and
pushes the overall moisture axis farther north than other
guidance, just not to as extreme a degree as seen 24 hours ago. 
At least the GEFS mean dampens some of the most questionable
details of the GFS, and again the ECMWF/CMC and their means
ultimately push the band of greatest moisture a little west of the
islands by Sunday-Monday while slightly higher surface pressures
prevail.   

Rausch