Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Apr 20 2020

Valid 00Z Tue Apr 21 2020 - 00Z Tue Apr 28 2020

Today's guidance maintains the forecast of only light rainfall
across the main islands through the next seven days.  Early this
week a surface ridge axis should lie fairly close to the area,
allowing for lighter winds and some land/sea breeze influence for
showers aside from some persistent trades/windward shower focus
over the Big Island.  By midweek the strengthening of eastern
Pacific high pressure may promote broader easterly to
southeasterly flow.  Toward Thursday-Friday guidance shows a
multi-day trend toward a faster and flatter representation of the
upper trough that passes to the northwest and north of the state. 
As a result high pressure continues to build north of the state
earlier, establishing more typical trade flow/windward shower
focus by late this week and continuing at least into early next
week.  The front that stalls northwest of the main islands this
week is increasingly likely to remain to the northwest before
weakening and being pushed westward as trade flow strengthens. 
Most guidance suggests a little bit of shortwave energy could peel
off from the late week trough and drift over the islands for the
rest of the period, with trends/consensus again indicating that
the GFS/CMC could be a little deep.  This energy could promote a
little more rainfall but likely only to a modest degree as
precipitable water values remain within a standard deviation of
climatology.

Rausch