Volcanic Ashfall in Hawaii, June 7 to 19, 2023

Area Forecast Discussion
National Weather Service Honolulu HI
344 AM HST Wed Jun 7 2023

.SYNOPSIS...
A weak surface ridge north-northeast of the state will maintain
light to moderate trade winds, with local sea and land breezes
developing across sheltered areas of the islands into Thursday.
Trade showers will favor windward facing slopes during the night
and early morning hours, with showers forming over some interior
and leeward sections each afternoon. Locally breezy trade winds
will likely return from late Thursday and Friday into early next
week. This will bring a return to a more typical trade wind
weather pattern with brief showers focused mainly over windward
areas by this weekend.

&&

.DISCUSSION...
The southern end of a weak surface front, which appears to be
about 300 miles north of Lihue, is moving slowly toward the east-
southeast. In addition, the western end of a weak surface ridge
is about 300 miles north-northeast of Honolulu. The close
proximity of these features to the state is keeping the pressure
gradient relatively weak over the region early this morning. This
is producing light to locally moderate trade winds across the
island chain. The background flow have been light enough to allow
local land breezes to become established over leeward and
interior sections of each island overnight. The trade winds will
continue to transport brief light showers into windward facing
sections of some of the islands this morning. However, rainfall
totals are expected to be meager over most areas due to the
rather dry and stable atmospheric conditions.

The forecast guidance indicates the tail end of the front will
continue to move slowly toward the east-southeast, and gradually
dissipate through Thursday. The weak surface ridge will also
remain north-northeast of the region, so the light to moderate
trade winds will persist. In addition, dry and stable atmospheric
conditions will likely continue. Therefore, expect the pattern of
local afternoon sea breezes, followed by nighttime land breezes
to dominate the weather pattern into Thursday. This scenario will
keep showers focused over windward sections during the nights and
early mornings. Then clouds and showers will develop over the
interior and leeward sections of the islands each afternoon as
the sea breezes become established, followed by clearing over
these same areas as land breezes develop at night.

Once the front dissipates around late Thursday, a new surface
high will likely build far northwest of the area. This will cause
the pressure gradient to tighten across the islands, which will
result in the trade winds strengthening from Thursday night into
early next week. This will lead to a rather typical trade wind
weather pattern with windward and mauka showers. The trade winds
may be strong enough to allow a few showers to be transported to
leeward sections of some of the smaller islands, especially at
night. In addition, expect clouds and spotty showers to develop
each afternoon over the upslope sections of the leeward Big
Island.

&&

.AVIATION...
A frontal system passing to the north of the state will help keep
the pressure gradient weak and generate mainly light trade winds
across the islands through the forecast period. Thus, isolated to
scattered showers will be mainly confined to windward locations
this morning. Brief MVFR conditions may accompany any of the more
robust showers.

By early this afternoon, sea breeze development could help
initiate scattered showers along the leeward mountains and coasts.

No AIRMETs are currently in effect.

&&

.MARINE...
A cold front passing far north of the region will weaken the high
pressure ridge far north of the state. Trade winds will remain in
the light to fresh range today, and then strengthen from Thursday
onward as high pressure builds back into the region.

Small surf will continue along south facing shores as a mix of
background long period south and southwest (170-220 degrees)
swells continue into next week.

Surf along exposed north and west facing shores will see an out
of season west-northwest (300-310 degrees) swell, from former
northwest Pacific Tropical Cyclone Mawar, will fill in later
today. This swell will peak on Thursday, hold through Friday and
then slowly subside through the weekend.

Surf along east facing shores will remain small into Thursday due
to lower trade winds. A slight increasing trend will start
Thursday night as trade winds strengthen.

&&

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

&&

DISCUSSION...Houston
AVIATION...Thomas
MARINE...Bohlin