High Surf in Hawaii, May 17 to 18, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
847 PM HST Sun May 17 2020

.SYNOPSIS...
Moderate to locally breezy trade winds will persist through the
week. An increase in clouds and showers is expected overnight and
Monday, as moisture associated with a dissipated front moves over
the islands, primarily dampening windward areas. After this moisture
clears by mid-week, the trades will deliver a few brief windward
showers.

&&

.DISCUSSION...
Although a strong mid-level ridge will continue to keep the island
atmosphere stable, an area of increased low-level moisture
(associated with a dissipated front) will fuel an increasingly wet
trade wind weather pattern for the smaller islands tonight into
Monday night. The timing will be a little slower for the Big Island,
with showers not expected to significantly increase until later
Monday, then lingering through Tuesday night.

Persistent and seasonable high pressure to the N and NE will
continue to support moderate to locally breezy trade winds this
week, ensuring that the bulk of the incoming moisture focuses along
windward areas. After the frontal remnants clear the area, the
trades are expected to deliver random pockets of moisture that will
lead to periods of mainly windward showers, while leeward Big Island
will see afternoon and evening clouds and showers.

&&

.AVIATION...
High pressure north of the state will gradually shift northeastward.
Moderate, mostly dry, trade wind flow is expected to persist through
twenty-four hours and beyond. Clouds and showers will favor east and
northeast facing slopes and coasts both day and night. Sea breeze
driven cumulus build-ups over Leeward Big Island will dissipate
within the next few hours, but are likely to redevelop Monday
afternoon. Isolated MVFR conditions are to be expected in brief
showers, otherwise VFR conditions will prevail all areas.

As of 0600Z, A band of low clouds and showers associated with a cold
front passing to the northwest and embedded in the trade wind flow
could be seen on satellite approaching the main Hawaiian islands.
Shower activity will increase once this band moves onshore around
1000z. An AIRMET for mountain obscuration may become necessary for
Windward slopes of the smaller islands late tonight or early Monday.

&&

.MARINE...
A 1026 mb surface high centered 740 nm north of Oahu will drift
northeast during the next couple of days then become stationary
during the second half of the week. In doing so, the high will
continue to generate moderate to locally strong trade winds across
the area through the rest of the week. The remnants of an old front
is about to move through the islands tonight and Monday, causing a
temporary softening of the trades. Locally strong trades should
return by Monday night. A Small Craft Advisory (SCA) is currently in
effect to 6 am HST Monday morning, but is likely to be renewed to
beyond Monday night with the 4 am HST package goes out.

The current north-northwest swell will continue to steadily decline
through Monday. A series of west-northwest and northwest swells are
expected to produce small surf along north and west facing shores
through the rest of the week. Late afternoon surf observations of 8
foot sets and upheld by buoy data, have triggered a High Surf
Advisory (HSA) for the south facing shores. WAVE WATCH III suggest
the swell to continue into Monday. Therefore, the HSA is good to
until 6 pm HST Monday. A gradual decrease follows, but will be held
up by a series of small long period pulses for the rest of the week
resulting in medium size surf. Surf along east facing shores will be
small to mid size through the week due to limited upstream trade
wind fetch.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Monday for South facing shores of
all islands.

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

DISCUSSION...Birchard
AVIATION...Bedal
MARINE...Lau