Heavy Rain in Hawaii, July 2, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
314 AM HST Sat Jul 2 2022

.SYNOPSIS...
High pressure north of the state will keep breezy to locally
windy conditions in place through the 4th of July Holiday
weekend. Fairly typical trade wind weather will prevail today,
with showers favoring windward and mauka areas, with the Big
Island seeing more showers than smaller islands. An upper level
trough will pass over the islands tonight and Sunday, bringing an
uptick in showers to the island chain and sending a few more
showers into leeward communities. A more typical trade wind
weather pattern is then expected Sunday night through Friday,
with a gradual easing of the trades Tuesday through late next
week.

&&

.DISCUSSION...
Currently at the surface, a 1031 mb high is centered around 1100
miles north of Honolulu, and is driving breezy to locally windy
trades across the island chain this evening. Infrared satellite
imagery shows low clouds moving into windward slopes and coasts,
with some high clouds streaming over the state as well. Partly to
mostly cloudy conditions prevail in windward areas, with partly
cloudy skies in most leeward locales. Radar imagery shows
scattered showers moving windward sections of Kauai and Maui,
numerous showers moving into windward Big Island, and very little
shower activity elsewhere at the moment. Main short term focus
continues to revolve around trade wind trends and rain chances.

High pressure north of the islands will keep breezy to locally
windy conditions in place through Independence Day. Winds will be
strongest today, where some of the windier areas of Maui County
and the Big Island will see winds reach advisory levels at times.
In fact, winds at Kohala Ranch have been blowing at advisory
levels for the past several hours, with a peak wind gust of 56 mph
measured at 125 AM. Additionally, several other observation sites
on Lanai, leeward west Maui, and the Maui central valley have
been flirting with Wind Advisory speeds through much of the
night. With little change in the strength of the winds expected
today, the Wind Advisory has been extended through 6 PM this
evening. The gradient should relax just a bit tonight, but breezy
conditions are expected to continue through the remainder of the
Holiday weekend. A couple fronts will slide southward well to the
north of the islands early next week, and this should result in an
easing of the trades beginning Tuesday, with a further easing
into the moderate range expected Wednesday through Friday.

As for the remaining weather details, a trough aloft will
approach the islands from the southeast today, focusing the deeper
moisture over the eastern end of the state. This should keep a
showery trade wind pattern in place for the Big Island and Maui
this morning. Shower weather should continue over windward Big
Island this afternoon, and some leeward shower development is
expected as well. Meanwhile, shower activity should decrease to
minimal levels on Maui this afternoon. A fairly dry trade wind
pattern should hold in place on Oahu through the day, while a
band of low clouds and showers currently tracking toward Kauai,
should bring an uptick in shower activity here today.

The trough aloft will dampen out as it lifts northwestward
through the islands tonight and Sunday, but will drag some deeper
moisture northward and into smaller islands. As a result, we
should see an increase in trade wind showers statewide tonight and
Sunday. The brunt of the shower activity should continue to focus
over windward and mauka areas, however with the increase in deeper
moisture, a few more showers should reach leeward communities.
Additionally, conditions may destabilize enough to allow for a
thunderstorm or two Sunday afternoon on the Big Island.

Weak troughing aloft is forecast to linger over the islands
Sunday night through late next week, but drier boundary layer
conditions will overspread the state. This should bring a return
of more typical summertime trade wind conditions with passing
light showers moving through the islands, particularly at night
and during the early morning hours, with a stray shower reaching
leeward areas from time to time.

&&

.AVIATION...
Strong high pressure north of the state will bring breezy to
locally windy easterly trades through the forecast period. This
regime will help to concentrate most shower activity along the
windward coasts and slopes...especially for Maui and Hawaii
counties. There will be periods of MVFR ceilings and visibility
associated with any of the heavier showers. Expect isolated
activity elsewhere.

AIRMET Tango remains in effect for moderate low-level turbulence
downwind of the higher terrain of all islands.

AIRMET Sierra remains in effect for north through east portions
of the Big Island and Maui above 2500 feet due to tempo mountain
obscuration from low clouds and showers.

&&

.MARINE...
Robust high pressure far north of the area will sustain fresh to
strong trade winds across most of the state's coastal waters into
next week. Winds are expected to reach 30 knots, or near gale
force, in the Alenuihaha Channel and the waters south of the Big
Island. Threshold seas of 10 feet are also likely in those zones
through Saturday. Currently, a Small Craft Advisory is posted for
all coastal waters through Sunday afternoon. Winds will likely
stay elevated across most coastal waters into Monday, then scaling
back to the typically windier waters around Maui County and the
Big Island Tuesday into Wednesday.

No significant swells are expected along all shores into next
week. The strong trades will support rough and choppy surf along
east facing shores, but surf will likely stay below the advisory
threshold of 10 feet. The current small south swell will continue
to lower. Only very small, medium period, background south and
southeast swells are expected into next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Lanai Mauka-
Kahoolawe-Maui Windward West-Maui Leeward West-Kohala-Big Island
Interior-Lanai Windward-Lanai Leeward-Lanai South-Maui Central
Valley North-Maui Central Valley South-Windward Haleakala-South
Haleakala-Big Island North.

Small Craft Advisory until 6 PM HST Sunday for all Hawaiian
waters-

&&

DISCUSSION...Jelsema
AVIATION...Thomas
MARINE...Kinel