High Surf in Hawaii, April 6 to 8, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
333 AM HST Tue Apr 6 2021

.SYNOPSIS...
Breezy trade winds will persist into Wednesday as strong high
pressure holds far north of the state. Showers will favor windward
shores and slopes. Trade winds will decrease late Wednesday and
remain at moderate strength through Friday, leading to typical
trade wind weather. Trades may diminish this weekend.

&&

.DISCUSSION...
Breezy trade winds persist, and wet conditions continue over
windward portions of the islands this morning. A band of moisture
remains hung up on windward Maui County and the Big Island, but
additional moisture has spread to the other islands overnight.
Trade winds will remain locally breezy today and perhaps into
Wednesday. Showers will focus across windward terrain as shallow
pockets of moisture move along within trade wind flow.

Trade winds will decrease bay late Wednesday. A high to the north
of the islands will weaken and a low far northeast of the state
will drift westward. Trades will remain at moderate strength
through Friday. Models show a slow moving upper trough just east
of the state and an upper ridge to the west, keeping the islands
within stable trade wind flow.

There is some uncertainty in the weekend forecast. Models show
the low dissipating at the surface, and remnant moisture moving
over the islands in a weakening trade wind flow. However, ECMWF
shows the nearby upper trough deepening and possibly moving over
the islands, while GFS is keeping this feature a little farther
east. Heavy rainfall is possible, but it is too far out to tell at
this time.

&&

.AVIATION...
A nearly stationary 1040 mb surface high located far north of the
islands will maintain breezy trade winds across the area through
at least tonight. Hence, AIRMET Tango, for low level turbulence
will continue through at least 071000 utc.

Remnants of an old front remains hung up over the windward slopes
of Molokai, Maui and the Big Island, where AIRMET Sierra for
mountain obscuration is in effect. Surface observations from
windward sites of these islands indicate that the ceilings have
lifted to above 3k feet. This usually means VFR, but persistent
rain will keep the AIRMET going until further notice. A new shower
area with widely scattered showers is pushing through the islands
now. So any improvements to windward areas of Molokai, Maui, and
the Big Island, will come later this morning. Do expect a few of
these passing showers to reach well into the leeward sections of
the smaller islands this morning. In the afternoon, a few showers
is possible over the lee side of the Big Island.

&&

.MARINE...
High pressure north of the islands will keep fresh to strong
trades in place through Wednesday. The trades will trend down
Thursday as the high north of the state weakens, with light to
moderate trades expected Friday through the weekend. A Small Craft
Advisory (SCA) is now in effect for all waters through 6 AM
Wednesday. The SCA will likely need to be extended for some
marine zones through Thursday and possibly Thursday night, while
other waters gradually fall below SCA thresholds.

The current north-northeast swell will hold fairly steady through
Wednesday, then slowly decline Thursday through the weekend. This
will keep surf along north and east facing shores elevated
through the work week, before surf drops to near or slightly below
normal levels this weekend. A High Surf Advisory remains is now
in effect for east facing shores through 6 PM Thursday, and may
need to be extended through Thursday night and possibly Friday.
This swell may also produce surges in north facing harbors such as
Kahului and Hilo.

South shore surf will remain small through the work week, with
mainly background south swells moving through. A larger long-
period south swell is expected to give surf a boost over the
weekend into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Thursday for east facing shores
of Kauai, Oahu, Molokai, Maui, and the Big Island.

Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian
waters.

&&

DISCUSSION...Powell
AVIATION...Lau
MARINE...Jelsema