Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu Apr 13 2023

Valid 00Z Fri Apr 14 2023 - 00Z Fri Apr 21 2023

Trade winds are forecast to gradually decrease in strength from
breezy to more moderate levels on Thursday into Friday as high
pressure to the north of Hawaii (between 35-40N latitude) shifts
east and weakens as a cold front well north of the islands
disrupts the high. A showery pattern is likely to continue on
Thursday with above average moisture levels and some instability
possible due to a weak trough overhead. Available moisture looks
to decrease late week into the weekend with a drying/more stable
trend possible as an upper ridge moves in.

After that, model guidance continues to indicate a likely pattern
change next week. Early in the week, models show agreement for
upper and surface lows to develop northwest of the state, with the
first effect for Hawaii being winds turning southeasterly ahead of
the associated cold front, possibly around Monday. These lows are
forecast to drift slowly eastward Tuesday-Thursday toward the
state. But differences in the timing remain, as do differences in
if/where the front focusing moisture could stall. At least the
western islands are likely to see significantly increased moisture
and shower/thunderstorm coverage sometime around midweek next week
with the tropical moisture plume along/ahead of the front.
Confidence is low in impacts for the islands farther east as
models differ with their frontal placement, with some solutions
sweeping the prefrontal moisture eastward across the whole state,
and some stalling the front west of the islands to maintain
moisture over Kauai and nearby islands. The forecast will need to
be refined with time given the low confidence in the specifics of
this pattern change.

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