Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Fri May 13 2022

Valid 00Z Sat May 14 2022 - 00Z Sat May 21 2022

The latest guidance over Hawaii continues to agree that a
significant pattern change is on tap, leading to a wetter regime
by the middle of next week. Through this upcoming weekend, expect
trades to weaken and take on a little more of a southeasterly
component as eastern Pacific high pressure weakens and a wavy
front sharpens to the west of the state. The combination of upper
ridging and somewhat below normal precipitable water values should
keep most of the windward-focused showers on the light side. By
next week, models and means all show a central Pacific upper
trough with embedded low (part of a Bering Sea into Pacific Rex
block pattern) approaching from the northwest, likely reaching its
greatest amplitude around early Wednesday before it starts to lift
out. This system will likely result in stronger and more southerly
winds, especially over the western islands, by next
Wednesday/Thursday. The GFS/ECMWF runs and their ensemble means
all show a significant increase of moisture by midweek, though the
GFS continues to be a little faster/farther east than consensus.
This would bring heavier rain totals farther east towards the
western main islands/Kauai than other models would suggest. The
GFS behavior can be an occasional bias of the model, though
differences remain well within typical predictability/error ranges
for forecasts several days out in time. A blended approach more
towards the ensemble means/ECMWF is preferred at this time. After
this system, upper ridging looks to build back in over the region
with trades shifting back towards more normal/breezy.

Santorelli