Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Sun Mar 19 2023
Valid 00Z Mon Mar 20 2023 - 00Z Mon Mar 27 2023
Latest guidance continues to show a transition from light
southerly flow this weekend with fairly light showers southeast of
a stalled wavy front toward more southeasterly flow and some
increase of moisture as an upper low closing off northwest of the
state supports low pressure development in its vicinity.
Models/means still significantly diverge with respect to important
details in terms of effects on the main islands. As has been the
case with the model over recent days, the 00Z ECMWF/12Z ECMWF mean
are on the western side of the spread with the overall system,
bringing the eastern periphery of the band of enhanced moisture no
farther than the far western islands before more typical trade
flow late week through the weekend pushes the moisture away.
Continuing from yesterday, the 00Z GFS is on the eastern extreme,
bringing its axis of highest precipitable water values as far east
as the eastern islands during the latter half of the week. Among
other guidance, the GEFS mean is a bit less extreme than the GFS
(moisture axis reaching the central islands) while the CMC is
essentially a compromise and the UKMET is close to the ECMWF.
Preference for a specific scenario is with continuity by way of an
intermediate solution represented by the 00Z CMC or modest
compromise with the GEFS mean. This would lead to some increase
in showers over the western and possibly central islands for a
time Tuesday onward, before establishment of more typical trade
flow by the weekend brings somewhat drier air in from the east.
Also by late week/weekend, guidance diverges considerably for what
could be a fairly deep new upper low well northwest of the state.
Even with these differences, the upper system and leading surface
front do not appear to get close enough to the state to have a
significant impact on the pattern for the main islands. However
the GFS is more enthusiastic than other guidance for leading
shortwave energy that the model brings toward the state from the
southwest during the weekend, so would lean away from those
details as well.