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Area forecast discussion 
National Weather Service Honolulu HI
1000 am HST Monday Apr 27 2015

Synopsis...
a weakening front will stall and dissipate over the eastern half of
the state. Strengthening northeast trade winds behind the front will
spread to The Big Island today. Persistent showers remain anchored
over northeast sections of the islands...and will be greatest in
coverage across Maui County. Breezy trade winds and active windward
showers will continue through much of the work week.

&&

Discussion...
water vapor imagery shows an upper level trough just east of the
state...with a high approaching from northwest of Kauai. At the
surface...a weakening front is nearly stationary between Maui and
The Big Island...with high pressure building far north-northwest of
the state. 12z radiosonde observations from Hilo and Lihue show weak low-level
inversions near 4kft...with the primary inversion strengthening near
9kft. Precipitable waters range from 1.08 inches at Lihue to 1.40
inches at Hilo. Early morning mimic total precipitable water imagery
shows the highest moisture focused near Maui County/Big
Island...with drier air spreading across the state from the north.

The old front is currently located over the Alenuihaha Channel...and
continues to weaken. Moisture associated with this front will keep
conditions cloudy and showery across much of Maui County...as well
as northern portions of The Big Island. Strong north-northeasterly
winds have spread across much of the state on the north side of the
front...and will strengthen across The Big Island as the front
weakens and dissipates. While winds are strong across the smaller
islands...we do not currently anticipate a Wind Advisory. The setup
is conducive to gusty winds especially across leeward sections of
the islands...but the ingredients do not look like they support Wind
Advisory criteria of sustained 30 miles per hour/gusts to 50 miles per hour.

As the front dissipates through tonight...high pressure will
continue to build north of the state. This high will keep a strong
gradient across the islands...with breezy trades expected for the
next several days. Remnants of the old front in the form of a weak
trough may weaken the gradient a touch on Tuesday...but guidance
shows stronger winds again on Wednesday. In addition to the winds...
pockets of moisture embedded in the trades will keep conditions
showery across windward sections. After a brief drying trend to
showers on Wednesday...additional moisture is expected late in the
week. While most of the rain will be focused across windward
sections...because of the strong winds some of these showers will
spread to leeward sections as well.

The 12z runs of the GFS and European model (ecmwf) both show the high shifting east
and weakening late in the week...as a new front pushes in from the
west. There remain some differences with respect to this next
system...but it remains well to the north and there are minor
differences to sensible weather across the islands. Trade winds are
expected to remain in place through the weekend...with showers
mainly across windward sections.

&&

Aviation...
a stationary front lingers near the Alenuihaha Channel. Low clouds
and showers continue to bank up along sections of the Maui County
islands. Airmet Sierra is posted for mountain obscurations along
north through east sections of Maui...Molokai...and Lanai. Prevailing
MVFR conditions...mainly for lowered ceilings are affecting several
airports on these islands...including phmk...phjh...phog...and
phny. VFR conditions are expected to slowly return to the terminals
throughout the day...however expect north through east slopes to
continue to carry tempo MVFR conditions and airmet Sierra.

VFR conditions will prevail on Kauai and Oahu...however...the
elevated trade winds will help push enhanced moisture back towards
them. North through east slopes may experience periods of MVFR
conditions today and into tonight. Airmet Sierra for mountain
obscuration can not be ruled out completely.

A strong high pressure far northwest of Kauai has built in behind
the front and has brought fresh to locally strong trade winds over
Maui County through Kauai with strongest winds over mountain ridges
and valleys. Airmet Tango for low level turb is posted for areas
south through west of the terrain from Maui County west through
Kauai. Morning amdar reports show a weak inversion between 2 and 3
thousand feet...with winds nearing 30 knots at this level.

As of 20z The Big Island sits west of the front and is still under
a light east to southeast flow. The high pressure is forecast to
continue to track east as the stationary front dissipates
throughout the period...this should allow for the trade winds to
gradually fill in near The Big Island and for clouds and showers to
be focused along the north through east sections.

&&

Marine...
the expected large northerly swell will continue to spread down the
island chain. The Hanalei buoy has been reporting combined seas near
15 feet...and the Maui buoy is also a couple feet higher than
wavewatch guidance. This swell will continue into Tuesday before
gradually diminishing...with high surf conditions for north and east
facing shores.

The strong high building north of the state combined with the large
north swell will lead to Small Craft Advisory conditions across
most areas. These conditions will likely continue into Wednesday
for these areas...and even through much of the week for the
typically windier areas.

&&

Hfo watches/warnings/advisories...
high surf advisory until 6 PM HST Tuesday for Niihau-Kauai
windward-Kauai leeward-Oahu North Shore-Oahu koolau-Olomana-
Molokai-Maui windward west-Maui Central Valley-windward
Haleakala.

Small Craft Advisory until 6 am HST Tuesday for Kauai northwest
waters-Kauai windward waters-Kauai leeward waters-Kauai Channel-
Oahu windward waters-Oahu leeward waters-Kaiwi Channel-Maui
County windward waters-Maalaea Bay-Pailolo Channel-Alenuihaha
Channel.

&&

$$

Ryshko

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