High Surf in Hawaii, May 15 to 16, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST Fri May 15 2020

.SYNOPSIS...
Trade winds will strengthen to moderate to locally breezy levels by
Saturday, and then continue through next week. Just a few brief
windward showers are in the forecast through the weekend, with the
potential for increased showers early next week.

&&

.DISCUSSION...
A seasonable trade wind flow will is returning as surface high
pressure builds N of the islands, and afternoon cloudiness over most
leeward areas will dissipate soon after sunset. The building high
will support moderate to locally breezy trade winds from Saturday
through next week, delivering limited low-level moisture through the
weekend. A ridge aloft will keep the island atmosphere very stable,
so showers are not expected to amount to much, occasionally
affecting windward areas. Increased low-level moisture associated
with a dissipated front is expected to arrive Sunday night, and may
fuel an increase in windward showers into the middle of next week,
with a few sprinkles potentially spreading leeward.

&&

.AVIATION...
High pressure to the state's northwest will strengthen and shift
northward over the next twenty-four hours. This will usher in a
return to more typical trade wind regime by Saturday. Shower
activity this afternoon is limited and focused over island interiors,
but is expected to become focused along east and northeast facing
slopes and coasts by Saturday morning.

In the meantime, weak flow across the islands today has allowed
light sea breezes to predominate most areas this afternoon. Sea
breezes are expected to abate shortly after sunset and give way to
light trade winds. Partial clearing is expected along Leeward coasts
and Interior Big Island after sunset.

Isolated MVFR conditions are to be expected in brief showers,
otherwise VFR conditions will prevail all areas.

&&

.MARINE...
A large, long-period northwest swell will increase seas tonight and
Saturday around Kauai and most windward waters. As a result, a Small
Craft Advisory (SCA) has been issued for hazardous seas in these
areas. A surface ridge north of Kauai will lift northward and
strengthen through the weekend. Trades are returning this afternoon
and will increase to moderate and locally strong levels through this
weekend and much of next week. The SCA will likely be  expanded to
include the windier waters around Maui and the Big Island later
tonight or Saturday morning.

Surf will be on the rise along north and west facing shores through
tonight as the aforementioned northwest swell fills in. The swell
will peak tonight into Saturday, with advisory level surf expected
along most exposed north and west facing shores of the smaller
islands. A High Surf Advisory (HSA) is in effect tonight through
Saturday. This swell will keep surf above seasonal norms through
most of the weekend, before diminishing early next week. A small,
long-period west-northwest swell could give surf a slight bump
Tuesday night through Thursday.

Elevated surf is also expected along south facing shores during the
next few days as a series of southerly swells move through the area.
South shore surf should trend up slightly on Sunday, and could reach
HSA level. Surf will lower early next week, with only small swells
expected Tuesday through late next week. East shore surf will remain
small through the weekend, then trend up slightly early next week as
trades strengthen over and upstream of the islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Saturday for North and West facing
shores of Niihau Kauai Oahu and Molokai and for North facing shores
of Maui.

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

&&

DISCUSSION...Birchard
AVIATION...Bedal
MARINE...TS