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Area forecast discussion 
National Weather Service Honolulu HI
330 am HST Wednesday Apr 1 2015

Synopsis...
the remnants of a low level trough over the west half of the island
chain will continue to gradually dissipate today. The trades will
return across the area and become locally strong by this
afternoon...with showers favoring windward and mountain areas
through Friday. Enhanced moisture southeast of the state could bring
increasing shower activity over The Big Island during the upcoming
weekend.

&&

Discussion...
the lingering cloudy skies and showers across the islands this
morning will continue to gradually decrease as an upper level
shortwave trough NE of the Aloha state moves further away from the
area. Also..the remnants of a low level trough will gradually
dissipate near Oahu today. This is allowing for surface high pressure
centered far north-northeast of the state to re-establish and bring a more
robust trade wind pattern across the islands...with showers again
focusing over windward and Mauka areas. Model guidance is also
showing subsidence developing aloft behind the departing shortwave
trough...which is helping in bringing a more stable airmass across
the area.

At 315 am HST...the latest data from the Doppler weather radar
network was showing most of the remaining showers across the islands
lingering over the Koolau Range in Oahu...windward Maui and the southeast
slopes of Mauna Loa over The Big Island. Meanwhile...cloud motion on
latest infrared satellite imagery suggest that winds across the
state are shifting to a more east flow...signaling the return of the
trades. Wind speeds will gradually strengthen through the rest of
the morning hours...becoming rather robust by this afternoon. This
trade wind pattern will further shift shower activity into windward
and mountain areas. Only exception will be the leeward Big Island
where onshore flow should bring afternoon cloud cover and a few
showers.

For the rest of the work week...the trade wind weather regime is
expected to prevail through Friday...a solution still supported by the
European model (ecmwf) and Canadian models. GFS...on the other hand...remains as the
outlier by bringing another collapse of the trades starting late Thursday
and into Friday...with a very moist airmass filtering at the middle levels
from SW and S of the islands. The reason for this synoptic scenario
is an approaching middle/upper trough from the northwest...which GFS seems to
be having trouble handling its evolution and eventual solution
during the late Thursday to Friday time frame. This results in a
considerably more aggressive rain event for the upcoming weekend
compared to the rest of the guidance. Thus...it seems reasonable to
keep following the European model (ecmwf) solution at this time...with a less aggressive
weakening trend of the trades on Friday...and wait for upcoming model
guidance before making any significant adjustments to the ongoing
forecast philosophy.

For the upcoming weekend...it is likely that enhanced moisture southeast of
the state will bring increasing showers across The Big Island late
Sat and into sun. Trade wind showers should continue early next week
with model guidance showing stronger trades developing across the
area as a strengthening high pressure system remains centered far
north-northeast of the Aloha state.

&&

Aviation...
rebuilding trade winds and increased stability are expected today.
Limited moisture within the trade wind flow will focus rain showers along
windward slopes and coasts...where isolate MVFR visible/ceiling can be expected.
Airmet Tango for low level turbulence to the west and SW of terrain is
likely to be issued. VFR will be the prevailing condition at the
terminals...although periods of MVFR ceiling are expected at phny around
mid-day...with brief MVFR visible/ceiling in rain showers possible at phli and phto.

&&

Marine...
latest readings from the ascat scatterometer product show winds in
the Alenuihaha Channel already at advisory levels. Thus...a Small
Craft Advisory has been issued for the windier waters around The
Big Island and Maui County. The strong east winds should continue
through at least Thursday evening...and the advisory could be
extended beyond Thursday if the strong winds persist.

A small northwest swell will gradually dissipate today. A small
south-southwest swell is expected to arrive during the second half
of the work week.

&&

Hfo watches/warnings/advisories...
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-Big
Island southeast waters.

&&

$$

Discussion...reynes
aviation...birchard

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