Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
816 am HST Sat Dec 27 2014
lowered the low temperature forecast for the next few nights with
weakening north winds and below normal dew points expected. Temperatures will
drop into the low 60/S along the coast and into the 50/S in some
light northerly winds and cool temperatures will prevail through the
weekend. Clouds and light showers will linger mainly over north
through west slopes. Trade winds will briefly return Sunday and
Monday. A weak front will move southeast across the state from
Tuesday into Wednesday shifting winds out of the west. A stronger
front may bring heavier rainfall late in the week.
surface observations around the main Hawaiian islands reported
generally light northwesterly to northerly winds. However...cloud
motions...sounding data...and radar data...to say nothing of
observations from The Big Island summits...all supported the
presence of very strong winds not too far above the rather low
inversion. Surface winds pushed low clouds ashore along northerly
slopes...though with subsidence prevailing aloft...and the
relatively dry air mass below...precipitation across the state was
minimal. Stable cloud cover was comparable to climatology in areal
extent though. Northerly advection kept temperatures on the low
side. Broadly speaking...this scenario should remain in place into
Sunday...but local winds will turn northeasterly by Sunday night
or Monday morning.
By Monday night...another front will approach from the northwest.
Solutions generally depicted this feature as weaker...and receiving
less support from aloft...than the last front. Still...consensus did
expect this front to hold together long enough to approach The
Big Island by Wednesday. With the air mass still dry...and ridging
aloft only starting to break down...rainfall and winds accompanying
the front likely will be quite modest.
From Wednesday into Thursday...guidance hinted that a much stronger
middle-level trough will dig south sharply toward the islands...
supporting the approach of a more substantial front. If consensus is
right...then next Thursday night into Saturday may be rather wet.
More recent model runs have begun connecting the two frontal
passages into one large event...with the middle-level trough deepening
earlier from Tuesday into Wednesday...and then deepening again from
Thursday Onward. At the surface...the first front in this scenario
would moisten the low levels slightly before passing over the state
and partly dissipating to the southeast...but then redeveloping
with the continuing support from aloft...and strong moisture
convergence at low levels. The second front then would move over
the state from the northwest...while the reinvigorated first front
spreads rain over The Big Island and Maui County from the southeast.
This scenario remained speculative...but may need to be incorporated
into the official forecast if solutions continue to lean in this
surf heights along north-facing shores are expected to remain below
advisory levels through Tuesday. A moderate northwest swell will
peak this afternoon...and then diminish Sunday. A short-period
north swell will arrive Sunday...and decrease into Tuesday. A
northwest swell is expected to build surf to near advisory levels
from Tuesday through Thursday.
Over the coastal waters...wind speeds and combined seas are expected
to remain below the threshold for a Small Craft Advisory.
High Wind Warning until 6 PM HST this evening for Big Island