Drought in Hawaii, August 16 to 31, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
827 PM HST Mon Aug 15 2022

.SYNOPSIS...
A weakened high pressure ridge north of the Hawaiian Islands will
keep a hybrid wind pattern in place with lighter background trade
winds over windward zones and sea breezes over leeward sections of
each island during the day. This lighter and more variable wind
pattern with island interior clouds will last into Wednesday,
then the high pressure ridge will begin to build back in north of
the region. Trade winds will strengthen from Wednesday night
onward into the moderate to locally breezy range from Thursday
through early next week.

&&

.DISCUSSION...
The satellite picture this evening shows fairly stable clouds over
the eastern half of the state. Radar imagery is detecting isolated
to scattered shower coverage with slower motion in the shower
bands due to the weakened trade winds. The windward areas of
Molokai, Maui and the Big Island are showing the most shower
activity so far this evening with more limited coverage elsewhere.

A long wave trough far north of the region continues to break down
down the subtropical ridge north of the state and decreasing the
trade wind flow into Wednesday. As these large scale trade winds
weaken, local scale land and sea breezes will strengthen over the
islands. This hybrid wind pattern will continue for the next two
days with land and sea breezes over leeward areas and light trade
winds over the windward zones. Clouds and a few showers will tend
to favor afternoons along convergence areas between the trade
winds and sea breezes over leeward and island interior sections.
Brief showers are also possible in this hybrid wind pattern over
windward zones in the overnight to early morning hours. A minor
wrinkle to this forecast is a passing low level trough drifting
south of the state on Tuesday and Wednesday. Deeper moisture
moving up the eastern side of this trough may slightly increase
clouds and shower activity over the Big Island and Maui. Chances
for thunderstorms increase over the mountain slopes of the Big
Island from Wednesday afternoon to evening as surface heating
along the slopes of Mauna Loa and Mauna Kea may trigger deeper
convection and isolated thunderstorms in the unstable layer above
the trade wind inversion height.

The long wave trough will weaken and drift further northeastward
from Wednesday into Thursday, allowing the ridge build back in
north of the island chain and strengthen the trade winds across
the region. We will transition back to a trade wind pattern on
Wednesday evening as the high pressure ridge builds back in.
Expect moderate to locally breezy trade winds from Thursday
into early next week with land and sea breezes fading. Clouds and
brief passing showers will trend back towards the windward and
mountain sections of each island, favoring the typical overnight
to early morning hours.

&&

.AVIATION...
Light to moderate trade winds flow will continue to steer ragged
bands of clouds and light showers off the Pacific towards mainly
east facing slopes and coasts. A capping inversion aloft around 07
kft will inhibit most shower activity at lower elevations, but
locally heavy showers over interior Big Island and Upcountry Maui
will remain a concern. A trough forecast to pass south of the
islands on Tuesday could yield isolated thunderstorms over higher
elevations of the Big Island in the afternoon and early evening
hours.

Current satellite imagery (as of 8 pm HST Monday) reveals Windward
portions of the Big Island and Maui to be enveloped in a broad
band of mostly stable clouds. AIRMET Sierra for mountain
obscuration will remain in effect for these areas. Conditions are
expected to persist overnight. Elsewhere, VFR flight conditions are
expected to prevail at most locations with only brief MVFR
ceilings and visibilities in passing showers.

&&

.MARINE...
The ridge north of the state will weaken, producing gentle to
moderate trades tonight into Wednesday. This pattern will allow
for localized overnight land breezes and daytime sea breezes near
the coasts. Pockets of fresh breezes can induce choppy conditions near
some coasts due to the combination of daytime heating and
terrain- induced accelerations. A return of fresh to strong
easterly trades is expected during the second half of the week as
the ridge builds to the north. This may lead to Small Craft
Advisory conditions for the windier waters and channels over the
eastern end of the state by Thursday.

Surf along south facing shores will remain small from the
combination of background south and southeasterly swells through
the rest of the week. Recent activity near New Zealand will lead
to an upward trend in surf along south facing shores beginning
this weekend and lasting into early next week.

Surf along east facing shores will remain small through the first
half of the week as the trades ease. A return of choppy/short-
period surf is expected by the end of the week through the weekend
as the trades return.

Small, surf along north facing shores will trend down to near
flat summertime conditions tonight through Wednesday, as the
current small, short period north northwest swell moves through.
North facing shores may see another round of small surf Thursday
through the weekend as few small, short period, north and
northwest swells move through the area. Surf may continue to trend
up early next week as a slightly larger and longer period
northwest swell moves over the area.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Almanza