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fxhw60 phfo 211956 
afdhfo

Area forecast discussion
National Weather Service Honolulu HI
956 am HST Tue Feb 21 2017

Synopsis...
gusty trade winds will continue through the week as strong high
pressure remains north of the state. Clouds and showers will favor
windward and Mauka areas, with brief showers passing over leeward
locations. Winds will diminish over the weekend as an area of low
pressure develops north of the islands. Showers may increase early
next week, as tropical moisture moves into the area from the
south.

&&

Discussion...
strong high pressure north of the state is propelling gusty trade
winds across the islands today. Scattered showers moving along
with the trades are affecting mainly windward areas with a few
showers reaching leeward locations of the smaller islands. This
weather pattern will continue through the week as transient high
pressure areas traverse from west to east across the North
Pacific.

Overnight soundings from Lihue and Hilo show a strong inversion
between 7 and 8 thousand feet which is capping low level clouds
and showers. However, above the inversion, the soundings are
indicating cold temperatures aloft and a layer of midlevel
instability. This instability is due to a passing upper level
trough that has dropped 500 mb temperatures near -15 degrees
celsius. This layer of instability has been in place the last few
days and has set off afternoon thunderstorms over the highest
slopes of The Big Island. Isolated thunderstorms are expected
again this afternoon with a chance of brief snow showers at the
summits of Mauna Loa and Mauna Kea. The upper trough will linger
through Wednesday before exiting to the east Thursday.

Global models are showing a change in the weather pattern over the
weekend and next week. A near- gale low is expected to form along
a passing cold front, and then linger north of the islands into
next week. The Current Island forecast has trade winds weakening
over the weekend and then winds turning from the east southeast
early next week. The wind speed and direction are highly
dependent on the low's location and strength so the forecast from
Sunday into early next week is highly fluid. The low will also
bring moisture from the tropics up and over the islands early next
week, increasing shower coverage and intensity.

&&

Aviation...
high pressure northwest of the Hawaiian islands will bring gusty
northeasterly trade winds to the terminals through the taf period.
This will allow for mostly VFR conditions to prevail with brief
MVFR trade wind showers. Showers will be focused across mainly
windward and mountain areas, although a few showers are
anticipated to make it into leeward areas. Northeasterly winds
will gust to 20-30kts for the terminals at times this afternoon,
decreasing slightly overnight, before returning again on
Wednesday. Stronger winds with gusts to 45 kts can be expected
across the channels, over higher terrain, and across mountain
valleys.

Aside from trade wind showers, mid-level instability will bring
the possibility of an isolated thunderstorm with snow showers for
The Big Island summits this afternoon.

With gusty winds, airmet Tango for turbulence below 8,000 feet is
anticipated to remain in effect over and immediately south
through west of mountains through tomorrow.



&&

Marine...
a high far northeast of the area is moving away to the northeast and
weakening. Winds have subsided a bit since yesterday, but a new
strong high far northwest of the area is moving east. Winds will
strengthen again today as the new high approaches. There will be
widespread strong trade winds over the coastal waters with near gale
force winds in the windiest areas around The Big Island and Maui. A
Small Craft Advisory (sca) is in effect for all Hawaiian coastal
waters through Wednesday evening. The advisory will likely be
extended, with Small Craft Advisory conditions possibly continuing through Friday for
the windiest areas around The Big Island and Maui.

The current north northwest swell will continue to subside through
tonight. A new northwest swell arriving Wednesday may produce surf
approaching advisory levels along north and west facing shores
tonight and Wednesday. A northwest swell arriving Friday may be
slightly larger and will likely continue through early next week.

&&

Hfo watches/warnings/advisories...
Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian
waters-



&&

$$

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