Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
813 AM EDT Wed Jun 13 2018

Valid 00Z Thu Jun 14 2018 - 00Z Thu Jun 21 2018

Currently, the Hawai`ian island chain remains bounded by a pair of
upper anticyclones to its west and east, respectively.
Mid/upper-level moisture is rather bleak based on recent water
vapor imagery with only a few light radar echoes showing up early
this morning. Looking ahead, the weakness in the flow aloft should
continues its slow eastward progression ultimately forming a
582-dm low along 140W longitude by 16/1200Z. This forms a rex
block for the days ahead with models showing the upper low
exhibiting a gradual westward jog. The 00Z ECMWF ensemble members
are west of the 00Z GEFS solutions but this would still keep the
longwave trough east of the state.

At the surface, a northward retreating dome of high pressure
should remain situated over the eastern Pacific which will
encourage the persistence of light to moderate trades across
Hawai`i. As the center of the ridge migrates north of 40N
latitude, weakening surface gradients should lead to a slackening
in the trades by the weekend. Based on the latest guidance, this
will remain a recurring theme as surface winds remain in the 5 to
10 knot range into the early/middle part of next week. This
ultimately will affect the coverage of trade driven shower
activity with models supporting less spatial extent of
precipitation. Before this, the guidance does appear to be a bit
more generous although total columnal moisture should only range
around 1 to 1.25 inches which is just below mid-June climatology.


Rubin-Oster