Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 210632
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
832 PM HST Fri Apr 20 2018

.SYNOPSIS...
Breezy trade wind weather is expected over the weekend with
clouds and showers focused over windward areas. Some of these
showers will blow over to leeward locations on the smaller
islands, while the Kona side of the Big Island will see afternoon
clouds and showers. Trades will strengthen to locally windy
levels next week.

&&

.DISCUSSION...
High pressure far northeast of the main Hawaiian islands is
driving locally strong trade winds across the state this evening.
Radar shows scant shower activity upwind of the islands, but
satellite loop shows layered clouds lingering across Maui county
and the Big Island. Afternoon soundings showed PW in the 1.1 to
1.5 inch range with increasing stability.

Models show the high pressure to the north will keep trade winds
on the breezy side through the forecast period, gradually gaining
strength and spreading westward over the weekend and into next
week. Clouds and showers brought in by the trades will favor
windward and mauka areas, but leeward areas may get wet from time
to time as well as winds increase. The layered mid and upper level
clouds will continue moving eastward, clearing Maui County
tonight and the Big Island Saturday morning. Drier and clearer
weather is then expected through the rest of the forecast period.

&&

.AVIATION...
A ridge of high pressure to the north of the state will keep a
moderate to breezy trade wind flow in place through Saturday.
Clouds and light showers will favor windward and mauka areas
through the period, with occasional MVFR cigs/vsbys expected. VFR
conditions will prevail in leeward areas.

AIRMET Sierra is in effect for mountain obscuration over windward
sections of Kauai, Oahu, Molokai, Maui and the Big Island.
Conditions will likely remain in place through much of the night.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the terrain of all islands. These conditions
are expected to continue through Saturday. AIRMET Tango also
remains in effect for moderate upper level turbulence between
FL250 and FL450. These conditions will likely continue through
most of the weekend.

&&

.MARINE...
A surface high north of the area will move northeast through
Saturday. The high is producing locally strong trade winds over
Hawaiian waters. A Small Craft Advisory (SCA) continues for
strong trade winds in the windier areas near Maui County and the
Big Island. A new high building northwest of the area will cause
the trade winds to strengthen further this weekend. The SCA will
likely be expanded starting Saturday.

Surf is expected to remain below High Surf Advisory (HSA) thresholds
along all shores through this weekend. Surf along east facing
shores will remain rough through Sunday night due to the trade
winds, but heights will remain moderate. There will be some
increase in surf heights along east facing shores next week as
trade winds strengthen.

A small northwest swell will build tonight and peak tomorrow. A
slightly larger swell is expected to arrive Sunday evening and
peak Monday. Another moderate swell is possible next Thursday.

Surf along south facing shores will remain small through early
next week. Lows in the southern hemisphere may strengthen and
shift east enough to produce some bigger surf along south facing
shores by the end of next week.

See the Collaborative Surf Discussion for more information.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Powell
AVIATION...Jelsema
MARINE...Donaldson



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