Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
822 AM EDT Wed Apr 04 2018

Valid 00Z Thu Apr 05 2018 - 00Z Thu Apr 12 2018

Latest guidance continues to highlight the potential for periods
of heavy rainfall over parts of the state in association with a
moisture-focusing frontal boundary that may linger over or near
the area for multiple days.

From now into Friday deep layer moist southwesterly flow will
prevail as a cold front approaches from the northwest.  Strong
dynamics passing by to the north will help to push the front into
and perhaps through the area, but with an axis of precipitable
water values reaching into the 1.50-2.00 inch range persisting
over the state.  Trailing surface ridge aligned along 30N latitude
will support northeasterly/easterly low level winds from Friday
into the weekend, which will lead to a windward focus for
rainfall.  Today there is somewhat better consensus on upstream
low latitude shortwave energy approaching from the west during the
weekend.  This energy may lead to some surface troughing for a
period of time while holding the axis of greatest deep moisture
over the state.  Depending on the solution, it is possible that a
portion of the shortwave energy may remain in the vicinity of the
islands into next week to encourage areas of enhanced rainfall. 
The relatively small scale of this energy aloft lends itself to
below average predictability for specific details.

Guidance consensus still shows another area of high pressure
building north of the state by next Tuesday-Wednesday, which will
serve to strengthen the trades and renew the windward focus for
rainfall.  With some upper ridging sliding to the north as well,
there are signals that the enhanced moisture may finally move
westward by the middle of next week.

Rausch