Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 150659

Area Forecast Discussion
National Weather Service Honolulu HI
859 PM HST Wed Nov 14 2018

Light winds will continue into Thursday, with trade winds
returning late Thursday and Thursday night. An increasing moist
and unstable airmass will bring the possibility of thunderstorms
and locally heavy rainfall Thursday night into the weekend. High
pressure north of the island should maintain a trade wind flow,
but the upper trough moving over the islands will provide the


Have made some modifications to the PoPs and associated fields,
but the flavor of the forecast remains the same. Clouds have been
increased in the forecast particularly over the western islands as
high clouds continue to stream in from the west. Radar and rain
gages have shown some showers moving over the Puna district on the
Big Island, and over the windward slopes of Haleakala, so have
also boosted PoPs over those areas for tonight. Anticipate some
improvement overnight.

A cold front to the northwest of the islands will continue to track
to the east, with a high far to the northwest. The front is not
expected to pass over the islands, but the moisture associated
with it will get caught in the trade wind flow over the coming
days and primarily impact the windward and mauka areas.

A mid to upper level trough developing just northwest of the
islands will strengthen over the islands and bring colder
temperatures aloft, providing enough instability that could
produce some thunderstorms and locally heavy rainfall. Still some
pieces to work out, but continue to have the possibility for
Thursday night into the weekend, with the main threat being over
the windward areas.

Trades will increase over the weekend and the mid to upper level
trough will slowly make its way down the island. The GFS shows
this trough weakening as it moves southeast of the Big Island
late Monday.


Light winds this evening will gradually give way to increasing
trades late tonight into Thursday. The trades are not expected to
be strong enough to require AIRMET TANGO through Thursday.

A relatively dry and stable airmass over the state overnight will
begin to destabilize on Thursday as a mid-level trough pushes in
from the northwest. The more unstable atmosphere combined with
increasing trade winds will cause showers to become more frequent
over windward sections, with areas of MVFR conditions and mountain
obscuration possible, especially later in the day. AIRMET SIERRA
may be required for mountain obscuration at that time. There will
also be a slight chance of thunderstorms over at least windward
sections of the state beginning late Thursday or Thursday evening.


Light easterly winds are expected through Thursday night as a
front passes by far north of the area. High pressure will build
back in north of the area on Friday and remain in place through
the weekend. Trade winds will likely become strong enough
requiring a Small Craft Advisory over the typically windy waters
around Maui County and the Big Island.

The current north northwest swell will continue to decrease
tonight and will drop below advisory levels later tonight. A new
advisory level northwest swell is expected to arrive Thursday
night, peak on Friday, then lower gradually Friday night and
Saturday. A slightly smaller north northwest swell is expected
Saturday night and Sunday. Another small to moderate size
northwest swell is expected to arrive on Monday. Small, mainly
background south swells are expected through the remainder of the
week and on through the weekend. A slight uptick in short period
choppy surf can be expected Friday through Sunday as the trade
winds pick back up.

An upper level trough expected to be over the area Thursday night
through Saturday, will cause the airmass to become unstable over
the area with heavier shower and isolated thunderstorms becoming a


High Surf Advisory until 6 AM HST Thursday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui
Windward West-Maui Central Valley-Windward Haleakala.



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