High Surf in Hawaii, January 14 to 19, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
350 AM HST Thu Jan 14 2021

.SYNOPSIS...
A weak stationary front will dissipate across the central islands
today. A second front is expected to approach from the northwest
tonight and Friday, then stall just northwest of Kauai Friday
night and Saturday. A third and stronger front is forecast to move
through the area Sunday into early next week, potentially
bringing some heavy rainfall to portions of the island chain.

&&

.DISCUSSION...
Currently at the surface, a front is nearly stationary over Maui
County this morning. Meanwhile, a 1019 mb high is centered around
400 miles north-northeast of Honolulu. Infrared satellite imagery
shows partly cloudy conditions over most of the state, with some
more extensive cloud cover over windward sections of Oahu, Molokai
and Maui. Radar imagery shows scattered showers over windward
areas from Oahu to Maui, with some showers spilling leeward as
well. Elsewhere, very little shower activity is seen. Main
forecast concern revolves around the potential for unsettled
weather late in the weekend through early next week.

Today...
The front is expected to dissipate today, as the high north of
the islands builds rapidly eastward. Moderate trade winds are
expected across the island chain, although the approach of the
next in a series of fronts may ease the trades enough over the
western islands this afternoon to allow for localized sea
breezes. Scattered showers are expected in close proximity to the
front this morning. A drier and more typical windward/mauka
focused shower pattern is expected this afternoon, although a few
leeward showers may develop due to sea breeze development.

Tonight through Saturday...
The next front will approach from the northwest tonight and
Friday, then stall out and gradually dissipate around 100 miles
northwest of Kauai Friday night and Saturday. Light and variable
winds are expected to persist over the western islands during this
time, with overnight land breezes and daytime sea breezes.
Meanwhile, light to moderate east to southeast winds should
prevail over the eastern end of the state. Fairly dry weather is
expected to continue through the period statewide, with no
significant rainfall expected.

Saturday night through next Wednesday...
Forecast uncertainty increases considerably late in the weekend
through the first half of next week, as model consensus and
individual model run to run continuity remains poor. What the
models do agree upon however, is that another cold front will
approach and move into the islands late in the weekend. What they
disagree on is the progressiveness of the front, with the GFS
showing an island clearing frontal passage, while the ECMWF hangs
the front up over the island chain. There is the potential that a
very wet pattern could set up across at least portions of the
state Sunday through early next week, with heavy rainfall and
thunderstorms not out of the question. Given the uncertainty,
will follow a blended forecast approach until details become more
clear. This will result in keeping rainfall in the forecast
statewide through the entire extended period.

&&

.AVIATION...
Radar shows a thin line of showers, marking the remnants of the
front, draped across West Maui through Molokai. These showers
appears to be dwindling.

In the wake of the front's passing earlier in the evening, low
level moisture is hung up over windward Oahu. This moisture has
the potential in turning into scattered showers later this
morning. A patch of clouds currently 50 miles southeast of Kauai,
poses a threat to that island this afternoon, as the prevailing
easterly trade winds, veer to the southeast by this afternoon.
Oahu, Molokai, and Lanai, may also encounter a few afternoon
showers as the easterly trade winds give way to sea breezes.

No AIRMETs right now. Do expect some spotty/isolated MVFR
ceilings/showers this morning, especially the windward and
mountain areas of Molokai and Oahu. AIRMET Sierra may eventually
be needed mountain obscuration on any of the smaller islands late
this morning. The Big Island looks fine right now. The lee side
of the Big Island will likely go through its usual morning sun,
then afternoon/evening clouds with a few showers.

AIRMET Tango for high level turbulence between FL320/420 will
be extended as the core of the jet max passes north of the
islands this morning. The AIRMET could be lowered by 22z.

&&

.MARINE...
A stationary front over Maui County will dissipate today.
Moderate to fresh northeast to east trade winds will briefly
return, as a high pressure system passes by north of the island
chain. Wind directions will then veer towards the southeast and
weaken tonight through Friday ahead of another cold front
approaching the islands from the northwest. A Small Craft Advisory
(SCA) remains in effect for most Hawaiian coastal waters through
Friday morning due to a large northwest swell moving through the
region spreading 10 to 16 ft seas over most of our coastal waters
and channels.

A series of large north to northwest swells will impact the state
through the weekend. The current building northwest swell
will peak today then gradually lower tonight. A brief overlapping
northerly swell (350-360 direction) will arrive tonight, peaking
on Friday. Warning level surf is forecast for north and west
facing shores of the smaller islands today and tonight. Surf
heights along the north facing shores of the Big Island will build
to advisory levels today. Warning level surf heights over the
smaller islands will lower to advisory levels Friday.

An extra large northwest swell (310-330 direction) will arrive
Friday evening, quickly building to warning levels Saturday
morning according to the Wave Watch III forecast at the Waimea
Buoy. These large swell heights will produce surf well above warning
thresholds, holding through Saturday, and then slowly lowering
from Saturday night through Sunday. Surf along north and west
facing shores of the smaller islands will remain well above warning
levels through the weekend. The northwest swell event this
weekend has the potential to produce the largest surf of the
season.

Another extra large northwest swell (300-330 direction) builds
into Hawaii waters on Monday. Wave Watch III holds warning level
surf from Monday into Monday night. This northwest swell
diminishes Tuesday as another north swell (340-360 direction)
builds into Hawaiian waters, with moderate swell heights holding
through Wednesday.

Surf along south and east facing shores will remain small through
the first half of next week. Some larger surf may wrap into east
facing shores exposed to the north and northwest swells.

A combination of the large surf this week coinciding with peak
monthly high tides may worsen beach erosion along shorelines
exposed to north and west swells during the early morning hours.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Friday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Surf Advisory until 6 AM HST Friday for Big Island North
and East.

Small Craft Advisory until 6 AM HST Friday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Alenuihaha Channel-Big Island Windward
Waters.

&&

DISCUSSION...Jelsema
AVIATION...H Lau
MARINE...Morrison/Bohlin