High Surf Warning 3, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
333 AM HST Fri Jan 21 2022

.SYNOPSIS...
Expect winds to increase a bit today as high pressure builds
north of the state. Winds will further increase to moderate
strength this weekend and push an area moisture over windward
slopes, followed by brief drying late Sunday into Monday. Another
increase in trade wind showers is possible late Monday and
Tuesday.

&&

.DISCUSSION...
A ridge near Kauai will keep winds light this morning. Expect
overnight land breezes to give way to daytime sea breezes by this
afternoon, especially across the western islands, as light trade
winds begin to spread westward. Cloud and shower coverage will
increase across mauka areas with sea breeze development, followed
by clearing at night. Models show surface high pressure will build
north of the state while a front stalls and begins to dissipate
just north of Kauai. Conditions will be rather dry at first, but
moisture from the dissipating front may affect windward Kauai and
Oahu beginning tonight.

Trade winds will continue to increase to moderate strength on
Saturday as high pressure holds north of the state. Winds will
shift out of the northeast on Sunday as a weak surface low
approaches from the east. Moisture from the dissipated front
should clear out, leading to a decrease in showers over all
islands Sunday afternoon. An upper low dropping southward to the
east of the state will produce increased north winds on the high
summits of the Big Island.

Expect trade winds to remain in place through next week, possibly
becoming breezy and gusty by Wednesday. The surface low will
fall apart, but its remaining moisture will fuel windward rainfall
for parts of the state late Monday and Tuesday, especially for
the Big Island and Maui. Expect a boost in trade winds mid week as
a reinforcing area of high pressure passes north of the state.

&&

.AVIATION...
A cold front approaching the islands from the northwest will keep
a high pressure ridge in place over state. The stability under
this ridge will limit shower activity today. Light large scale
winds will allow local scale land breezes to continue this
morning. Winds will begin to transition back to trade winds today with
sea breezes lingering over terrain sheltered western slopes of
each island. Isolated showers remain in the forecast mainly along
convergence bands between the returning trade winds and the
afternoon sea breezes.

No AIRMETs are in effect, and none are anticipated.

&&

.MARINE...
Light and variable winds will hold today over the western end of
the state, while a return of moderate to fresh trades is
anticipated over the eastern end. Trades are expected to fill in
statewide tonight through the weekend, potentially reaching the
strong category over the typically windier locations around Maui
County and the Big Island, as high pressure builds north of the
area in the wake of a passing front. Trades may shift to a more
northeast direction early next week as the islands become
positioned between low pressure passing to the southeast and the
ridge to the north.

Surf along exposed north and west facing shores will trend up
through the day today as a new, west-northwest swell builds down
the island chain. Offshore buoy observations (51101/51001)
quickly ramped up overnight (mostly in line with predicted
levels). This swell has already reached the Hanalei buoy and
should begin showing at the Waimea buoy (it's back in action -
thanks to the PacIOOS folks) through the morning hours, beginning
around or by sunrise. Guidance depicts the surf peaking tonight
through Saturday above warning levels (XL category) followed by a
gradual downward trend through the second half of the weekend. The
warning has been issued for exposed north and west facing shores
of the smaller islands and will need to be expanded to include the
leeward section of the Big Island in the afternoon package today.
Small Craft Advisory has been issued over western end of the state
to account for the seas expected to reach the 10 ft threshold
today, and will also need to be expanded down the island chain
later today.

Although a downward trend is expected through the second half of
the weekend, another long-period, west-northwest pulse arriving
by Sunday night will support a return of advisory-level (if it
dips below Sunday) surf Monday. Heights should then dip below
advisory levels for north and west facing shores Tuesday through
the second half of next week.

Surf along east facing shores may trend up over the weekend in
response to a tight gradient that has setup between low pressure
centered more than 1000 miles east of Hilo and high pressure to its
north. Recent ASCAT data showed a packet of strong- to gale-force
winds focused at the state north of the low. Guidance has this
easterly swell arriving by Saturday night, then lingering into early
next week before easing.

&&

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

Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters.

&&

DISCUSSION...Powell
AVIATION...Bohlin
MARINE...Gibbs