High Surf in Hawaii, March 10 to 11, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
351 AM HST Sun Mar 10 2019

.SYNOPSIS...
Breezy to locally windy trades are expected to prevail through
early Monday, with the trades easing late Monday and Monday night.
Moderate trades are expected Tuesday through Thursday, before
becoming light Friday into next weekend. Periods of showery
weather will move through the islands today through Wednesday
night, with windward and mauka areas being the favored targets.
Drier conditions are expected to develop on Thursday and persist
into next weekend.

&&

.DISCUSSION...
Currently at the surface, a 1032 mb high centered around 1000
miles northeast of Honolulu, is driving breezy trade winds across
the island chain early this morning. Infrared satellite imagery
shows mostly cloudy conditions in most windward areas with partly
cloudy conditions in most leeward locales. There is some scattered
to broken jet stream cirrus enhancing cloud cover over the
central and eastern islands however. Radar imagery indicates that
shower coverage has diminished over the smaller islands in the
last couple hours, while scattered to numerous showers continue
to move into windward sections of the Big Island. Another batch
of showers appears to be developing upstream of the smaller
islands however, and this area of showers is tracking westward at
around 25 to 30 mph. Main short term focus continues to revolve
around the strong trades and rainfall trends.

Model solutions remain in excellent agreement with the large
scale synoptic pattern through the forecast period. High pressure
will remain nearly stationary around 1000 miles northeast of the
island chain through tonight, before beginning to track eastward
on Monday. The high will then accelerate towards the west coast of
the continental United States Monday night through Wednesday as a
cold front passes by to the north of the islands. The front will
stall out and dissipate around 400 to 500 miles north of Kauai
Wednesday night, with a surface ridge axis settling slowly
southward through the remainder of the work week, and over the
western and central islands on Saturday. Breezy to locally windy
conditions are expected to prevail through Monday, although the
trade wind speeds should edge slightly lower on Monday. The trades
will continue to trend downward Monday night, then hold in the
moderate range Tuesday through Thursday, before becoming light
Friday into next weekend.

Today through Wednesday night,
Showery low clouds are expected to fill back in this morning
across the smaller islands while continuing to stream into the Big
Island. Some diurnal disruption is expected this afternoon
leading to a decrease in shower coverage across the state, with a
few showers also developing over leeward sections of the Big
Island. Bands of clouds and showers will then periodically move
through the islands through the middle of the week, with the
showers most prevalent during the overnight and early morning
hours. Windward and mauka areas will remain the primary receivers
of the showers through the period, but a few showers will drift
leeward from time to time.

Thursday through Saturday,
Trade wind showers are expected to continue for the end of the
work week, but there may be some interior and leeward shower
development on Friday if the trades weaken as expected. Light
winds will likely lead to daytime sea breezes and overnight land
breezes Friday night and Saturday, with showers favoring the
coastal waters at night and interior areas during the day.
Overall, rainfall chances should trend lower late in the work week
into next weekend as upper level heights build and the surface
ridge axis settles southward.

High clouds associated with a subtropical jet stream will hold
over the central and eastern islands today, although some
thinning of the cirrus is indicated by model time/height relative
humidity cross sections as the day progresses. The high clouds
are expected to retreat to the east of the state tonight.

&&

.AVIATION...
Surface high pressure north-northeast of Hawaii will keep
moderate to possibly strong northeasterly trade winds in place
through the period. AIRMET Tango for low-level turbulence below
8,000 ft remains in place and is expected to remain through
the day and possibly into Monday. Upper-level turbulence between
FL270 and FL420 should dissipate later in the morning.

Low-level moisture associated with showers continues to affect
windward slopes, therefore AIRMET Sierra for mountain obscuration
is in effect for the windward areas of all islands above 2,500 ft.
MVFR conditions are expected for these areas, otherwise most
leeward areas in the state will continue to see VFR conditions.

&&

.MARINE...
Strong trade winds associated with high pressure centered north-
northeast of the state will continue into Monday, then gradually
trend down into the moderate to strong category Tuesday through
midweek as a weakness within the ridge develops. A combination of
strong winds locally and upstream of the state along with a
moderate northwest swell in place have led to advisory-level seas
over exposed waters. The latest buoy observations showed seas
running near to a few feet above predicted levels. Seas will
remain rough through Monday, then gradually begin to ease by
midweek as the winds trend down.

Surf along north and west facing shores will hold at advisory
levels this morning then drop below through the afternoon hours
as the northwest swell lowers (northwest offshore buoys have
already begun to lower this morning). Overlapping reinforcements,
however, expected out of the same general direction Monday,
Thursday and Friday night will be enough to keep the surf up each
day through next weekend. The first reinforcement will fill in
through the day Monday and peak by Monday night, then lower into
midweek. The second one is expected to begin filling in Thursday,
peak by Thursday night, then lower into the weekend. Heights
should remain below advisory levels as these sources peak. The
third reinforcement expected to fill in Friday night will be much
smaller, but hold into the weekend. For the long range, guidance
shows a gale low tracking southeast across the Date Line Friday
through Saturday. A captured fetch associated with this source
setting up within the 310 to 340 directional bands relative to the
islands could drive the surf up locally by the end of next
weekend. Confidence, however, remains low being this far out.

Surf along east facing shores will remain rough into the upcoming
week due to the strong onshore winds, likely holding around advisory
levels through Monday night before lowering. This downward trend
will continue through the week and into next weekend as the
upstream fetch weakens and the local winds drop into the light to
moderate category.

The first south swell of the season currently in place along
south facing shores will peak today, then gradually lower Monday
through Tuesday. Small background reinforcements through the week
should be enough to support small surf continuing each day.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until noon HST today for Niihau-Kauai Leeward-
Waianae Coast-Oahu North Shore-Molokai Leeward.

High Surf Advisory until 6 AM HST Tuesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian
waters-

&&

DISCUSSION...Jelsema
AVIATION...Chevalier
MARINE...Gibbs