Winter Storm Warning 3, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
846 PM HST Wed Mar 1 2023

.SYNOPSIS...
Wet and windy conditions will persist across much of the state
through Thursday, with a gradual decline in the trades expected
Friday and Saturday. Showers will be more active along windward
slopes while strong trade winds periodically carry showers over
leeward areas. A low aloft will produce a few downpours and
thunderstorms during the next few days, with highest potential for
thunderstorms expected on the Big Island. Winds will decrease and
veer southerly Saturday night and Sunday ahead of an approaching
front. A series of front will then move through the islands next
week, bringing moderate to breezy southwest winds to the area, and
shifting the favored areas for rainfall to the west through south
facing slopes and coasts.

&&

.DISCUSSION...
Currently at the surface, a 1038 mb high is centered around 950
miles north-northeast of Honolulu, while a surface trough is
positioned around 700 miles southeast of the Big Island. The
pressure gradient across the island chain remains very strong this
evening, with windy conditions prevailing statewide. Infrared
satellite imagery shows mostly cloudy conditions in windward
areas, while partly cloudy skies prevail in most leeward locales.
Radar imagery shows numerous to widespread showers moving through
windward areas, with coverage the greatest over the eastern end of
the state. Meanwhile, a few showers are reaching leeward
communities at times as well due to the strong trades. Main short
term concerns revolve around Wind and Winter Weather Headlines.

High pressure north-northeast of the state will gradually weaken
during the next few days, while a trough of low pressure lingers
to the southeast of the island chain. The trades will gradually
weaken during this time, but will remain windy through at least
Thursday and potentially through Thursday night. A High Wind
Warning (HWW) remains in effect for areas over and downwind of
the Kohala mountains on the Big Island through 6 AM Thursday, with
a Wind Advisory in place for the remainder of the state during
this same time. Winds should ease enough such that the HWW can be
cancelled with the morning forecast package, but a Wind Advisory
appears likely for most of the state through the day on Thursday.
The winds will continue to ease Thursday night and Friday, but
breezy conditions are expected to persist.

The trades will continue to ease over the weekend, with moderate
trades Saturday becoming light and variable on Sunday as a
weakening front approaches from the west. Winds are forecast to
pick up out of the southwest at moderate levels on Monday, then
become locally breezy out of the southwest and west Tuesday
through next Wednesday as a series of fronts move through the
island chain.

As for the remaining weather details, rather showery trade wind
weather will continue through Saturday, particularly over the
eastern end of the state. Some brief downpours and a rumble or
two of thunder will be possible over the eastern end of the state
through Saturday as well given the upper level disturbance
lingering overhead. We should see a pattern shift beginning
Sunday, with land and sea breezes leading to the development of
afternoon and early evening showers over primarily interior and
mauka areas. The typical leeward areas will become windward areas
beginning Monday and continuing through the middle of next week,
with showers favoring west through south facing slopes and
coasts.

A Winter Weather Advisory remains in effect for the high elevation
summits on the Big Island through 6 PM Thursday, where snow and
freezing drizzle are expected. Wintry weather will likely continue
to affect the summits through Saturday, and the Winter Weather
Advisory may eventually need to be extended.

We will continue to monitor conditions closely on the Haleakala
summit, as temperatures are forecast to remain just above freezing
and any slight dip could bring some wintry weather to the highest
elevations, at or above 10,000 feet.

&&

.AVIATION...
The high pressure system far north of the state will weaken
through the weekend. Strong and gusty trade winds are forecast to
continue for one more day before decreasing from Friday onward.
The combination of unstable conditions and strong winds will allow
clouds and showers to be enhanced by the mountains on each
island, producing scattered MVFR conditions with occasional IFR
conditions for windward and mountain areas. Most of the heavy
showers and isolated IFR conditions will be focused over the
eastern end of the state tonight, along with a continued isolated
thunderstorms over the windward areas of Maui and the Big Island.

AIRMET Sierra remains in effect for mountain obscuration over the
Big Island, Maui, Molokai, Oahu and Kauai. This AIRMET will
likely decrease in coverage by Thursday morning.

AIRMET Tango remains in effect for low level moderate to isolated
severe turbulence over and downwind of all island mountains.
AIRMET Tango also remains in effect for strong surface winds
across the entire state. These AIRMETs will likely continue
through Thursday.

Light icing is also expected IC from the Big Island to Molokai in
a layer 100-160.

&&

.MARINE...
Rough conditions with gales and large seas will continue into the
second half of the week as strong high pressure (1038 mb) remains
positioned to the north. Satellite data showed 25-35 kt winds
with seas hovering in the 12-15 ft range, which line up well with
buoy observations at the exposed PacIOOS Mokapu station and a
SOFAR drifter buoy that has entered the Alenuihaha Channel over
the past 24-hrs. Guidance supports gales continuing through
Thursday over the windier waters and channels of Maui County and
the Big Island, then dipping to advisory levels Thursday night
into Friday. A pattern transition is likely late Friday through
the weekend as a cold front approaches, which means a break in the
strong winds/seas. Guidance supports moderate to fresh southwest
winds early next week as the front moves into the area.

Surf along east facing shores will remain rough, with heights
holding around the warning threshold of 15 ft (faces) through
Thursday due to the aforementioned winds over and upstream of the
islands. A downward trend is expected late Friday through the
weekend as the ridge weakens and winds ease.

Surf along north facing shores will remain well below the
seasonal average each day through early next week, with the
exception of the shores exposed to the large easterly seas
wrapping in. A small west-northwest swell arriving Friday from a
recent gale that tracked eastward from the Kurils to the Date Line
will linger into the weekend. A small long-period pulse is
possible Tuesday out of the north-northeast from a gale predicted
to move through the Gulf of Alaska over the weekend. For the long-
term (low confidence), despite the differences shown in the
various model solutions, a more significant winter-like scenario
unfolding will become a possibility through the second half of
next week in response to broad low pressure evolving north-
northwest of the islands. Confidence through the extended portion
of the forecast should improve over the coming weekend.

Surf along south facing shores will remain near the seasonal
average each day, with mainly wind swell wrapping into exposed
areas.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 AM HST Thursday for Kauai Leeward-Kauai
Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-
Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-Maui
Leeward West-Big Island Interior-Kauai North-Kauai East-Kauai
South-East Honolulu-Honolulu Metro-Ewa Plain-Koolau Windward-
Koolau Leeward-Molokai-Lanai Windward-Lanai Leeward-Lanai South-
Maui Central Valley North-Maui Central Valley South-Windward
Haleakala-Kipahulu-South Maui/Upcountry-South Haleakala-Big
Island South-Big Island Southeast.

High Surf Warning until 6 PM HST Thursday for Olomana-Maui
Windward West-Kauai East-Kauai South-East Honolulu-Koolau
Windward-Molokai Windward-Molokai Southeast-Windward Haleakala-
Kipahulu-South Haleakala-Big Island Southeast-Big Island East-
Big Island North.

High Wind Warning until 6 AM HST Thursday for Kohala-Big Island
North.

Winter Weather Advisory until 6 PM HST Thursday for Big Island
Summits.

Small Craft Advisory until 6 PM HST Friday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters.

Gale Warning until 6 PM HST Thursday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Gibbs