Drought in Hawaii, January 1 to 31, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
846 PM HST Tue Dec 31 2019

.SYNOPSIS...
A high pressure system far to the northeast of the islands and an
approaching cold front northwest of the state will cause wind
speeds to decrease on New Years Day. A weakening cold front
approaching the islands from the northwest will spread clouds,
showers, and breezy trade winds across the Hawaiian Islands from
Wednesday night through Friday. A strong high pressure system
building in behind the front will keep breezy wet trade winds in
the forecast through the upcoming weekend. Trade winds continue
through the first half of next week at moderate levels with signs
of an upper level low lurking northeast of the island chain
possibly affecting the extended rainfall forecast.

&&

.DISCUSSION...
A high pressure system far northeast of the islands will interact
with a low pressure system and cold front roughly 500 to 600
miles northwest of the state keeping the islands in a light
background east to southeasterly wind flow pattern through
Wednesday afternoon. Wind speeds will remain light enough to allow
localized sea breezes to develop along western slopes of all
islands during the later morning to afternoon hours. Stronger
winds aloft will keep the highest summits of the Big Island in a
wind advisory through 6 AM HST Wednesday morning.

Local radar imagery this evening shows a few showers moving in
over the eastern slopes of Maui and the Big Island. Rainfall
activity tonight will remain on the drier side with isolated to
scattered bands moving into the windward and mountain slopes of
each island. Northeast trade winds will redevelop by Wednesday
evening, increasing in strength and spreading eastward across the
state through Friday.

On Thursday and Friday, a weakening cold front will move into the
islands from the west on Thursday. The latest model guidance
continues to show bands of showers and northeasterly trade winds
developing out ahead of the frontal zone. The cold front reaches
Kauai by Thursday afternoon with increasing low clouds and
showers spreading eastward from Kauai to Maui through the
overnight hours. Expect increasing trade winds through the period
peaking on Friday in the breezy to locally windy range. These
wind speeds may exceed our wind advisory thresholds and may
require a wind advisory by Friday morning for wind favored areas
of each island.

By Saturday and Sunday, a strong 1030+ surface high will build
into the Central Pacific basin keeping breezy trade winds in the
forecast. Wind directions will veer towards the east as the high
center passes through the region. A developing upper level low
east of the Hawaiian Islands and lingering moisture remnants from
the old frontal band will keep unsettled weather in the forecast
through Sunday.

Monday through next Wednesday, both the American (GFS) and
European (ECMWF) global weather models continue to show an
unstable cold core low developing east to northeast of the state.
However, model solutions are very inconsistent with the strength
and location of this system. This means that for now, our
confidence in precipitation coverage and rainfall amounts in the
extended range forecast remains poor going into the first half of
next week. However, our moderate to breezy trade wind forecast
will continue through next Wednesday with a high degree of
confidence. Keeping unsettled weather in the forecast for the
first half of next week as we expect both the GFS and ECMWF
models will continue to improve on the forecast location of this
unstable upper low center. More forecast rainfall details will be
provided as the forecast time period gets closer. Stay tuned.

&&

.AVIATION...
Easterly trade winds will trend down tonight, with winds light
enough by Wednesday for some localized land and sea breezes.
Limited clouds and showers will be around the islands through
Wednesday, with the focus primarily over windward and mountain
areas.

AIRMET Tango remains in place for mechanical low level turbulence
to the lee of the mountains, but the VAD Wind Profiles from the
4 radars are all showing weaker winds. Anticipate this AIRMET
being dropped by midnight.

VFR conditions will prevail, with some pockets of MVFR in passing
trade winds showers primarily over windward and mountain areas.
It is possible for some isolated pockets of IFR due to smoke from
holiday fireworks tonight, most likely during the hour or so
around midnight.

Afternoon soundings had a trade wind inversion at Lihue around
7000 feet, and around 8000 feet at Hilo.

&&

.MARINE...
A High Surf Warning remains in effect through tonight for most
north and west facing shores as a large northwest swell continues
moving across the area. This swell will gradually lower later
tonight through Friday. A smaller northerly swell is expected to
fill in Thursday night, then linger on through the weekend. A
rather small northwest swell is expected Sunday through Monday.
Surf along east facing shores will remain a bit elevated through
the remainder of the week and on through the weekend due to upwind
swell sources, as well as the expected increase in trade winds
later this week.

A Small Craft Advisory is posted for all Hawaiian coastal waters
due to breezy trade winds and elevated seas. Winds will drop off a
bit Wednesday and early Thursday but increase once again late
Thursday and on through the weekend as high pressure builds in to
our north. Seas will also remain elevated across most areas.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Wednesday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Windward Haleakala-Kona-Kohala.

Wind Advisory until 6 AM HST Wednesday for Big Island Summits.

Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian
waters.

&&

DISCUSSION...Bohlin
AVIATION...M Ballard
MARINE...Kinel