Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
830 PM HST Sat Feb 28 2015
thunderstorms have been flaring over portions of Maui and The Big
Island with additional heavy showers and thunderstorms expected to
pop up across the eastern end of the state through the night. The
forecast is on track this evening...and the previous discussion
below captures the scenario quite well.
a north to south oriented surface trough is located near The Big
Island. Moisture along this boundary combined with instability aloft
due to an upper trough will continue to produce locally heavy
downpours and thunderstorms across Maui tonight and The Big Island
into Monday. Trade winds will spread across the state on later
through Sunday as the trough weakens...but lingering enhanced
moisture and instability will remain near The Big Island over the
next several days.
Previous discussion 400 PM...
a weakening surface trough with a north-to-south axis is located
near The Big Island. Meanwhile...an upper level trough is located to
the north northwest of Hawaii with the base of the upper trough over
the western end of the state. Visible and infrared satellite shows
layered clouds along the midlevel jet steam moving across the
eastern and central portions of the state. Isolated embedded
thunderstorms are also present within the eastern portion of the
layered cloud band...and is affecting The Big Island and Maui late
Afternoon soundings show precipitable water values of 0.95 inches in
Lihue to 1.46 inches at Hilo indicative of the considerably drier
airmass has pushed into Kauai and spreading towards Oahu. 500 mb
temperatures were -15 c on the Lihue sounding and -13 c on the
Hilo sounding. The cold pool aloft associated with the upper level
trough is what is making the atmosphere unstable across the eastern
portion of the state...while the plentiful moisture near the trough
is allowing for heavy rain and thunderstorms to occur over Maui and
The Big Island.
Northeast trade winds continue to push eastward across the state
which is associated with a 1026 mb high centered northwest of the
state. Winds have strengthened on Maui...and will spread to The
Big Island tonight.
The upper trough will persist northwest of the state into early
next week. The trough will continue to push the deep layered
moisture up over The Big Island. This upper trough is causing the
strong winds aloft and prompted a Wind Advisory on The Big Island
summits. In addition...the deep moisture is reaching far enough up
to produce snowfall...icing and freezing fog on Mauna Kea and Mauna
Loa likely through at least Sunday night. A Winter Weather Advisory
remains in effect for these areas through Sunday night. At the low
levels...trade winds will direct moisture onto the windward slopes
for all islands. The abundant moisture near The Big Island will
keep the windward portion of that island the wettest.
A wet and breezy trade wind pattern will likely develop statewide
by Sunday night and Monday...then persist through at least the
middle of next week. A lingering middle/upper level trough overhead
will maintain somewhat unstable conditions aloft with the usual
middle level inversion likely remaining weak or absent. Model
consensus shows plenty of available low level moisture being
pushed against the terrain by brisk trade wind flow.
European model (ecmwf) and GFS models diverge somewhat toward the end of next week.
models keep strong trades in place...but the European model (ecmwf) pushes a drier
airmass south across the state while the GFS keeps moisture
further north in response to a developing low pressure area near
a surface trough near The Big Island and an elongated upper level
trough over islands are acting to produce unsettled weather...mainly
over Maui and The Big Island. Thunderstorm activity has become more
isolated...however potential remains through the night for areas of
Maui and The Big Island. Cloud tops to fl350 and IFR conditions
can be expected in thunderstorms. Airmet Sierra for mountain
obscuration remains posted for north through east facing sections of The Big
Island and Maui. Along windward areas of the the smaller
islands...periods of tempo MVFR are likely.
Airmet Tango is posted for moderate turb between fl250 and fl350
associated with a upper level jet moving over the islands. The
layered clouds moving over with the jet are thick enough to
suggested tempo light icing above 130.
a surface trough with a north-to-south axis is located near The Big
Island. This is resulting in gentle winds around The Big Island with
strengthening northeast trade winds over the smaller islands which
are under the influence of a high pressure system northwest of the
state. These winds will build eastward over The Big Island tonight.
A Small Craft Advisory for strong winds has been issued beginning
Sunday morning for waters near Kauai...and channels near The Big
Island and Maui County. In addition...the threat of thunderstorms
will continue over waters near the Bug Island and Maui through the
Breezy trades appear likely to continue through next week with the
possibility of expanding the Small Craft Advisory to other zones during the second
half of the week as winds strengthen further.
A north northwest swell will build on Sunday...producing North Shore
surf around the advisory level Sunday night and Monday. Smaller
north-northwest swells are due next week. See the collaborative
nearshore swell and wind forecast /srdhfo/ for more details.
Winter Weather Advisory until 6 am HST Monday for Big Island
Wind Advisory until 6 PM HST Sunday for Big Island summits.
Small Craft Advisory from 9 am Sunday to 9 am HST Monday for
Kauai northwest waters-Kauai leeward waters-Maalaea Bay-Pailolo