High Surf in Hawaii, March 30 to 31, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Sat Mar 30 2019

.SYNOPSIS...
Light winds with land and sea breezes over the islands will prevail
through Sunday as another front approaches the area from the
northwest. A weak front dissipating over the northern islands will
bring an increase in clouds and showers Monday. A surface high will
then move to north of the islands by the middle of next week,
heralding a return to trade winds to the area from Tuesday through
Thursday.

&&

.DISCUSSION...
A surface high pressure just west-northwest of the islands is
providing light northerly winds to the much of the islands this
afternoon while variable winds continue over the Big Island due to
the present of a weak trough just east of the island. Sea breezes
over the islands this afternoon will become land breezes overnight.
The strong winds over the Big Island summits have eased a bit, thus
the wind advisory has been cancelled. Afternoon Lihue sounding
continued to depict a dry and stable airmass, while Hilo sounding
still revealed a little more unstable airmass with seasonal amount
of moisture.

A convective weather regime will prevail across the area through
early part of Monday. Much of the islands will see mainly fair
weather with land breezes tonight as atmosphere remains dry and
stable under the light winds. Sea breezes will once again develop
over the islands during the day on Sunday, with afternoon and
evening clouds. The surface trough east of the Big Island is
expected to nudge west later tonight and may bring more clouds and a
little more showers to that island late tonight through Monday.
Showers will focus along windward and southeast sections.

An upper trough and its associated surface front are approaching the
main Hawaiian Islands from the northwest. This upper trough will
likely bring strong winds, possibly reaching advisory or even
warning levels and cold temperatures over the Big Island summits
late Sunday into Monday. The surface front is expected to weaken as
it moves to Kauai on Monday. This is due to the associated upper
level trough advances east swiftly. Moisture associated with the
weakening front will spread east across the state Monday through
Tuesday, bringing some showers. Winds will turn more northeast as a
new surface high is expected to move to the northwest of the islands
behind the front. Much clouds and showers are likely to affect
windward areas under the increasing northeast trade winds.

The surface high will slowly reach north of the islands by the
middle of next week, bringing trade wind weather to the area
Wednesday and Thursday. Looks like winds may weaken across the area
by the next weekend as another frontal system may pass north of the
islands.

&&

.AVIATION...
Relatively dry and fair weather with VFR conditions expected through
Sunday, with only isolated showers, mainly along windward coastal
areas. Otherwise, scattered stratocumulus clouds continue over the
state, as well as some afternoon cloud buildups over island
interiors with the relatively light wind flow. Strong low-level
inversions at PLIH and PHTO indicate a stable air mass, which should
continue to minimize the shower activity through Sunday. Winds will
shift around to the south and southwest and increase beginning
tomorrow afternoon ahead of an approaching, but weakening, front and
upper- level trough expected to arrive over the next couple of days.
No AIRMETs are expected through Sunday.

&&

.MARINE...
A weak "bubble" high passing just N of the islands through tonight
will continue to support light and variable winds that will tend to
be from the E over water. A shift to light to moderate S to SW winds
will briefly develop Sunday as the high dissipates and a front
approaches from the NW. As the front dissipates near Kauai and Oahu
Sunday night and Monday, a weak pressure gradient will lead to light
and variable winds once again. High pressure building N of the
islands Monday night and Tuesday will bring strengthening NE trade
winds, with moderate to fresh ENE trade winds persisting into
Thursday. The high will move well E of the area by the end of the
week, and as the associated ridge moves close to the islands, gentle
and variable winds are expected next weekend.

A shorter period NNW swell is gradually diminishing, just as a
longer period WNW swell is arriving. Surf heights along exposed N
and W facing shores will be elevated, but are expected to peak just
below advisory levels as the new swell peaks Sunday. Will continue
to monitor upstream buoy observations to ensure the swell isn't
bigger than expected. Another NW swell arriving Monday night/Tuesday
may peak near advisory levels before diminishing through Wednesday.
Yet another NW swell is possible by Friday, with initial indications
that peak surf heights with this swell will be below advisory
levels. Little in the way of surf is expected along S and E facing
shores, especially as the small S swell currently arriving
diminishes.

Trade winds may be sufficiently strong in the windier zones around
Maui and the Big Island around midweek to support the issuance of a
Small Craft Advisory (SCA). Otherwise, seas will approach 10 feet in
some zones when the aforementioned NW swell peaks Monday
night/Tuesday, thus requiring a SCA.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...Hui
AVIATION...TS
MARINE...Birchard