Drought in Hawaii, January 1 to 31, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
837 PM HST Thu Dec 31 2020

.SYNOPSIS...
A high pressure system slowly passing by north of the Hawaiian
Islands will keep breezy to windy trade winds in the forecast
through New Years Day. Breezy trades will continue through the
weekend with periods of passing showers drifting over windward and
mountain areas. More isolated shower activity may develop over
leeward slopes. Trade wind speeds will decrease to more moderate
levels, for the first half of next week, as a cold front passes by
north of the island chain.

&&

.DISCUSSION...
The big picture satellite imagery shows some unstable cumulus
clouds drifting into the state from the northeast direction on the
trade winds. These clouds will produce passing showers mainly over
windward and mountain sections of each island through New Years
Day. More isolated shower coverage remains in the forecast over
leeward areas. To the north, a weakening cold front is stalling
out roughly 300 miles north of Kauai as a high pressure system
drifts from west to east north of the front. A weak subtropical
jet stream will bring some scattered high cirrus clouds to the
islands enhancing sunrise and sunset colors.

The overall weather pattern remains unchanged tonight with a wind
advisory in effect for most of Maui and Hawaii Counties. The
strong northeast trade winds will continue through New Years Day
then become more breezy through the weekend. Trade wind speeds will
decrease to more moderate levels, for the first half of next week,
as a cold front passes by north of the island chain.The good news
is these strong trade winds will certainly blow out the New Years
Eve fireworks smoke away from most island communities fairly
quickly.

Passing showers in this extended trade wind weather pattern will
continue to favor windward and mountain areas, trending higher in
the overnight to early morning hours, with less rainfall activity
forecast over leeward areas.

Global weather models are in good agreement on this weather
pattern lasting through the next seven days. Expect subtle day to
day changes in the island rainfall patterns as small scale
convergence features in the upstream trade winds may produce some
differences in rainfall coverage and amounts.

Happy New Year!

&&

.AVIATION...
Breezy to windy trades will prevail through New Years Day as high
pressure slides by to the north of the island chain. Low clouds
and showers will favor windward and mauka areas, with some of
these showers spreading leeward due to the strong trades.

AIRMET Sierra is in effect for mountain obscuration across
windward sections of Molokai, Maui and the Big Island. This AIRMET
will likely continue through the night and may need to be expanded
to include windward sections of Oahu and Kauai.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the terrain of all islands. These conditions
will persist for the next couple days.

AIRMET Tango will likely be needed for moderate upper level
turbulence between FL250 and FL400, either late tonight or Friday
morning.

&&

.MARINE...
High pressure building north of the state will tighten the
pressure gradient back across the chain enough to strengthen trade
winds through New Years Day. Widespread strong trades will occur
over all local near and offshore waters Friday with near gales
expected over the windier channels. A Gale Watch is in effect for
the Alenuihaha Channel through Friday afternoon as winds may
frequently gust to gale force magnitudes. Winds are forecast to
weaken to more moderate to locally fresh speeds early next week as
the high shifts further east and relaxes the pressure gradient.
The combination of large northwest swells and strengthened trades
will create rough seas that will exceed the Small Craft Advisory
(SCA) sea height threshold of 10 feet across all Hawaiian waters
the next several days. An SCA is in effect for all waters through
Saturday afternoon.

A large northwest swell continues to fill in across the chain and
and will peak surf along north and west-facing shores during the
overnight hours. A steadily decline in surf will occur as these
swells gradually diminish Friday. Surf heights of greater than 30
feet along north shores, 20 feet along west shores, are anticipated
during tonight's peak. Latest northwest offshore buoy observations
are depicting a slight leveling off of these latest northwest
swells. This evening's readings are still holding fairly strong
with around 13 foot, 15 or 16 second swell energy moving toward
the state. Swells are expected to slowly veer more north as energy
steady declines Friday into Saturday. The new year will begin with
a series of weekend smaller, long period north northwest swells.
The combination of recently large swells and higher astronomical
tides may result in minor coastal water inundation within low-
lying areas during the New Year's morning high tides.

Surf along eastern exposed shores will increase tonight into
Friday in response to these amped up trades both locally and
upstream of the state. Surf along east-facing shores could reach
advisory thresholds Friday. With no anticipated incoming southerly
swell energy, south-facing shore surf should remain low even by
winter season standards.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM Friday for north and west facing
shores of Niihau Kauai Oahu and Molokai and north facing shores of
Maui.

Wind Advisory until 6 PM Friday for Lanai, Kahoolawe, Maui,
except Haleakala summit, and South Big Island, Big Island North
and East and Kohala.

Small Craft Advisory until 6 PM Saturday for all Hawaiian waters
except the Alenuihaha Channel.

Gale Watch through Friday afternoon for the Alenuihaha Channel.

Small Craft Advisory from 6 PM Friday to 6 PM Saturday for
the Alenuihaha Channel.

&&

DISCUSSION...Bohlin
AVIATION...Jelsema
MARINE...Blood