Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
347 AM EDT Wed Jul 20 2022

Valid 00Z Thu Jul 21 2022 - 00Z Thu Jul 28 2022

Today's guidance shows little change in the overall pattern, with
moderate to occasionally brisk trades into early next week as high
pressure north of the state settles over the east-central Pacific
during the weekend and beyond.  Trades may weaken a little by
Tuesday-Wednesday due in part to an upper weakness/low reaching
northeast of the state at that time.  Similar to recent days,
guidance consensus keeps precipitable water values below
climatology for most of the period but with at least one solution
that increases moisture to some degree at times.  Thus overall
expect the majority of showers to be focused over
windward/mountain areas and on the light side.

One continuing question mark is late this week when an area of
enhanced moisture passes by to the south.  The majority scenario
continues to be for minimal northward extension toward the Big
Island but the 12Z ECMWF mean still shows a little more moisture
reaching the area around Thursday.  The 00Z ECMWF/GFS/GEFS mean
are all drier.  There is still potential for small scale
low-predictability impulses over and northwest of the main islands
to have some influence on moisture, tempering confidence in an
exact forecast.  On the other hand, the late weekend/early next
week time frame has better confidence in being drier as upper
ridging passes overhead.  By Tuesday-Wednesday the ensemble means
and 00Z GFS agree on keeping PWATs fairly well below normal, while
the 00Z ECMWF shows slightly higher values over the Big Island and
vicinity.  As with late this week, low-confidence shortwave
details may play a role in moisture specifics.  Leaning toward the
majority seems most reasonable for now. 

Rausch