Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
330 am HST Thursday Dec 25 2014
an upper level trough and a developing surface low north of the
islands will continue to gradually move away from the area today.
This will bring a decrease in showers and a gradual transition to a
drier weather pattern for the upcoming weekend. Moderate northerly
and northwesterly winds will shift to a more typical trade wind
regime by late Sunday and into early next week.
the anticipated cyclogenesis north of the islands is finally happening.
Latest ascat scatterometer wind data shows the surface low developing
north of Kauai and Oahu as an upper level trough also gradually lifts
to the north of the area. As both these systems consolidate into a large
storm complex...their northeasterly motion will take the deep
moisture that brought all the rain activity from the last couple of
days further away from the island chain today. However...there will
be enough residual moisture for a few showers to develop
today...which will be streaming across the islands from the northwest. This
reflects the backing of the surface winds to a more west/northwest flow as the low
deepens north of the area.
With a drier and cooler airmass gradually establishing and the deep
layer moisture departing to our east-northeast...conditions across the islands
continue to improve and the Flash Flood Watch for Maui County and
The Big Island has been discontinued. Also...as the trough/low
complex moves further away from the area...the threat for blizzard
conditions over The Big Island summits has decreased and the warning
is no longer in effect. However...pressure gradients will remain
tight enough aloft...keeping periods of very strong winds through
the afternoon hours. Thus...a High Wind Warning is now in effect for
the Mauna Loa and Mauna Kea summits until 6 PM HST this evening.
The global models are still slow in depicting the development of
the aforementioned surface low north of the islands...but at least now both
GFS and European model (ecmwf) seem to be reaching better consensus in not developing
the low to the east of The Big Island as in previous runs. Thus...
confidence is high in terms of having the local weather conditions
becoming more benign along with cooler temperatures and northwest winds
developing today and through Friday. Winds will then gradually
switch to the north during the weekend...and finally turning back to a
more typical trade wind pattern late sun and into early next week as
a ridge moves to the north of the Aloha state. Little shower activity is
anticipated during the weekend.
Models depict a possible cold front reaching the islands by the
middle of next week...with potential for another round of unsettled
weather across the Aloha state. But confidence in this solution
remains low at this time.
the calm winds and localized land breezes overnight have kept the
islands fairly quiet. Winds should start to increase slightly today
as a low north of Kauai continues to develop. With the position of
the low...winds will range from northerly over Kauai...to westerly
over Oahu...to west-southwesterly over Maui County.
Isolated to scattered showers continue to speckle the smaller
islands...mainly over the waters. Some of these brief showers may
carry MVFR conditions and clouds tops between 10 and 12 kft.
Throughout the day...expect terminals to remain predominately VFR.
No airmets are expected.
a high surf advisory for north facing shores of the smaller islands
continues through today. Another moderate northwest swell is
expected to arrive Friday night...peaking on Saturday before
decreasing a little on Sunday. A reinforcing northwest swell will
arrive on Monday.
The combined seas heights are high enough to warrant Small Craft
Advisory for much of the exposed coastal waters. Conditions should
improve enough by this evening such that the advisory may be allowed
high surf advisory through 6 PM HST this evening for north facing
shores of Niihau...Kauai...Oahu...Molokai and Maui.
High Wind Warning for The Big Island summits until 6 PM HST this
Small Craft Advisory through 6 PM HST this evening for all Hawaiian
waters except for Maui leeward waters...Big Island leeward waters
and Big Island southeast waters.