Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Wed Apr 12 2023

Valid 00Z Thu Apr 13 2023 - 00Z Thu Apr 20 2023

A fairly strong surface high (about 1040 mb) to the north of
Hawaii, between 35-40N latitude, will keep trade winds at breezy
levels through Wednesday. Trades are forecast to gradually lessen
for the latter part of the week as the high shifts east and
weakens as a cold front well north of the islands disrupts the
high. A showery pattern is likely to continue Wednesday and
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 shows considerable variability with the
upcoming pattern over Hawaii. Early next week there continues to
be model agreement for upper and surface lows to develop northwest
of the state, with the first possible effect for Hawaii being
winds turning southeasterly. But by Tuesday-Wednesday there have
been notable differences with the timing/track of these lows.
Overall, recent model guidance (at least the 00Z GFS, ECMWF, and
GEFS mean) has slowed up compared to previous cycles with tracking
these features eastward, keeping the associated significant
moisture plume west of the islands through midweek. Meanwhile the
CMC is much quicker to track the lows eastward to the north of
Hawaii for a wetter pattern over the state before the cold front
sweeps across. Given the model and run-to-run differences,
confidence is low in the pattern and impacts. It remains possible
that at least the western islands (and perhaps the whole state)
see significantly increased moisture and shower coverage at some
point next week, but the forecast will need to be refined with
time.

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