Drought in Hawaii, December 1 to 31, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
850 PM HST Wed Nov 30 2022

.SYNOPSIS...
Mostly dry weather is expected through the weekend. Light to
moderate trade winds will strengthen somewhat over the weekend, but
will bring just a few brief windward showers through the period.

&&

.DISCUSSION...
High pressure passing far N of the islands is supporting gentle to
moderate NE trade winds this evening, while a building low-level
subsidence inversion is making for an increasingly stable island
atmosphere. With relatively low PWAT (near 1.25") over most of the
state, it is no surprise that radar is showing just a few small
showers, primarily over windward waters. Although radar returns over
interior and SE Big Island have diminished since earlier this
afternoon, several pyrocumulonimbus clouds (with abundant lightning
and little total rainfall), triggered by the ongoing eruption of
Mauna Loa, were observed during the late afternoon.

A relatively quiet trade wind weather regime is anticipated through
the weekend, with some changes potentially coming early next week.
Surface high pressure will become established far NE of the islands
over the next couple of days, supporting light to moderate NE trade
winds that will veer to the E on Friday as a persistent low to the
NE gradually moves E. A mid-level ridge will become established over
the islands, and moisture currently lingering near the Big Island
will diminish. Only meager rainfall is expected, mainly focused
over windward slopes and coasts, most likely during nights and
mornings. The exception will be over the upper-elevation Mauna Loa
lava flow, where pyrocumulonimbus clouds may occur with little to no
notice.

Forecast confidence for early next week has increased slightly over
the past 24 hours, as guidance has come into a little better
agreement as to the evolution of a strongly meridional flow over the
central north Pacific. A strong ridge aloft well W of the area will
allow for the downstream development of a cutoff low, with the low
currently expected to develop W of the islands Monday and Tuesday
before drifting W away from the islands. This leads to a
strengthening ridge aloft over the islands, and a relatively strong
surface high pressure cell to the NE that will support locally
strong E-SE trade winds. This may bring a subtle increase in
showers.

With Mauna Loa's emissions emanating at high elevations (around 10-
13 kft), the forecast does not anticipate vog or other volcanic
emissions having a significant impact on lower elevation populated
areas of the Big Island, or the other islands. We will continue to
monitor this dynamic situation for any potential changes to the
forecast philosophy. Worth noting that latest reports from the
Hawaii Volcano Observatory indicate that Pele's hair has been
observed in the Humuula Saddle.

&&

.AVIATION...
A high pressure system building in from the north will slowly
increase trade wind speeds into the moderate range through Friday.
Afternoon sea breezes will still hang on along terrain sheltered
slopes of all islands. Brief passing showers are possible over
windward airfields of the smaller islands with more numerous showers
expected along the windward Big Island slopes over the next 24 hours.

No AIRMETs in effect with possible MVFR conditions along the
windward Big Island slopes due to clouds and SHRA.

&&

.MARINE...
Large surface high pressure northeast of the islands will maintain
moderate trade winds through late Thursday. As this high sinks
southeastward, moderate trades will veer more easterly Friday and
persist well into next week. An approaching cold front from the
northwest may hang up just west of the state early next week and
veer winds more south of east.

Tonight's exiting northwest swell will gradually subside through
early Thursday morning. A larger west northwest (300-310 degree)
swell is forecast to build in from early Thursday into Friday. This
swell is anticipated to be large enough to increase north and west-
facing shore surf, due to the more westerly component of the swell
direction, to High Surf Advisory (HSA) levels for all islands
(except Big Island) as early as tomorrow morning. This swell may
push north and west surf heights up to near High Surf Warning (HSW)
thresholds at its peak Thursday night into Friday. This west
northwest swell may sneak into Big Island's western waters Friday
and increase the odds for placing their west-facing shores within a
HSA. A northeast swell moving into our nearshore windward waters
Saturday may also lift Big Island north-facing shore surf to around
HSA levels this weekend. East-facing shore surf may experience a
small bump as this northeast swell fills in Saturday night and
Sunday morning.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory for North and West facing shores of Niihau Kauai
Oahu and Molokai and for North facing shores of Maui from 6 am HST
Thursday until 6 pm HST Friday.

&&

DISCUSSION...Birchard
AVIATION...Bohlin
MARINE...Blood