High Surf in Hawaii, August 21 to 22, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
334 PM HST Sun Aug 21 2022

.SYNOPSIS...
A dry, breezy trade wind pattern will continue through early
Monday. Trades will gradually weaken starting late Monday,
allowing local night land breezes and afternoon sea breezes to
develop into mid-week. A disturbance aloft, along with increased
low-level moisture, may result in increased clouds and showers,
including interior and leeward areas Tuesday and Wednesday
afternoons. Trades are expected to strengthen again later this
week.

&&

.DISCUSSION...
Very little has changed since this morning. Visible satellite
imagery and radar continue to show relatively sparse clouds around
the islands with minimal showers. The 00Z soundings from Lihue
and Hilo both verify these conditions, showing a strong inversion
around 8 kft with slightly higher, but still low precipitable
water values. These stable conditions and surface high pressure
northeast of the state are keeping moderate to locally strong
trades in place over the islands as well. The dry trade wind
weather pattern will likely persist through early Monday, yielding
scattered low clouds and minimal shower activity along windward
facing sections, as well as clouds and some showers over the
leeward slopes of the Big Island each afternoon through Monday.

The surface high will weaken and drift east over the next few days,
easing the pressure gradient over the state. At the same time, a
mid-level trough to the east of the islands will move west toward
the region, with an accompanying weak surface trough possible as
well. This will cause the trade winds to weaken beginning tonight,
allowing a local nighttime land breeze and afternoon sea breeze
regime to become established around Tuesday. The forecast guidance
also shows an increase in low-level moisture with these approaching
troughs, which could lead to higher rain chances over windward
and mauka areas, as well as over most leeward and interior sections
once the sea breezes become established Tuesday afternoon.

The forecast guidance shows the surface ridge will begin to lift north,
as the parent surface high builds far to the northeast during the
second half of the week. This will allow the trade winds to strengthen
again late this week into the weekend. The mid-level trough will
also move west of the area at this time, for a return to overall
drier conditions.

&&

.AVIATION...
Surface high pressure north of the state will maintain moderate to
locally breezy trade winds through early Monday, with stable
conditions due to a ridge aloft. Expect VFR conditions to dominate
with isolated MVFR conditions periodically occurring over windward
areas in a few showers. Trades will begin a downward trend later
tonight.

AIRMET Tango for turbulence over and downwind of terrain below
8000 ft will likely remain in effect through early Monday.

&&

.MARINE...
No significant changes to the marine or surf forecast with the
afternoon package.

A ridge to the north of the islands will maintain moderate to
locally strong trade winds tonight, but the ridge is expected to
weaken and drift southward. This will start to weaken the
pressure gradient over the area later tonight. This will result
in a lowering of the trade wind speeds as Monday wears. A Small
Craft Advisory (SCA) remains in effect for the typical windier
waters around Maui County and the Big Island through tonight. As
the winds weaken, we expect the SCA to be dropped, with winds
remaining below SCA through Thursday. During the end of the
week, the ridge will rebuild, causing trades to pick back up.

The current long period south swell is expected to peak tonight
and into Monday. The latest buoy reports from the Barber's Point
buoy show the swell has remained nearly steady for the last
several hours. The resultant surf is expected to remain just
below advisory levels. This south swell will likely also help to
boost surf heights along west facing facing shores. Look for the
swell to decline Monday afternoon through the middle of the week.

Short period trade wind swell will lower as the trade winds
weaken during the first half of the week. A northwest swell is
forecast to move into the region on Monday, producing a slight
boost to north shore surf heights.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

DISCUSSION...TS/M Ballard
AVIATION...TS/M Ballard
MARINE...M Ballard