Gale Warning 7, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
1010 PM HST Sun Dec 15 2019

.SYNOPSIS...
Moderate trade winds will prevail today, then strengthen Monday,
with breezy conditions expected into Tuesday. The trades will trend
down Wednesday into Thursday, before increasing to locally windy
levels late Thursday into next weekend. The trades will continue to
deliver low clouds and showers to windward areas with the occasional
leeward spillover.

&&

.DISCUSSION...
Trade winds (at times quite strong) will prevail through the
upcoming week, supported by a pair of high pressure cells passing
far N of the islands, with the central pressure of the second high
expected to be anomalously high. Winds may turn SE next weekend as
low pressure strengthens W of the islands, with this low potentially
impacting island weather in just over a week from now.

Trade winds have eased somewhat over the past 24 hours, as a
weakness in the ridge is passing N of the islands. A new high
pressure cell is currently NW of the area, and will pass N of the
islands tonight and Monday, leading to increased trade winds until
another weakness in the ridge passes to the N around Wednesday. An
even stronger high is expected to pass N of the islands late
Thursday into Saturday, likely bringing another period of locally
strong trade winds heading into next weekend. Central pressure of
this high is expected to be an unseasonably high 1034 mb as it
passes, and model guidance indicates very strong trade winds at the
end of the week, with open ocean wind speeds of 30-35 mph near the
islands.

As low pressure deepens W of the area next weekend, the gradient
between the gradually weakening high and the developing low may
bring strong SE winds to the state. Confidence is somewhat
diminished as to the details, but model guidance has been fairly
consistent indicating a somewhat energetic weather pattern in about
a week from now as the low nears the islands.

In the meantime, expect passing windward showers and moderate trade
wind until trade winds increase on Monday. A weak mid-level
shortwave is now expected to pass from N to S over the area Monday
and Monday night. The combined effects of increased orographic lift
supplied by the increased trades, the passing shortwave, and
moisture associated with a frontal remnant caught in the trade flow
will likely lead to an increase in trade wind showers, and a
slightly wetter regime than previously thought.

A mid-level ridge will build over the islands Tuesday and Wednesday,
supporting a stable island atmosphere, but the trade winds should
still be able to muster a few windward showers. The mid-level ridge
will weaken Thursday and Friday, and increasing low level
convergence associated with the new high building N of the area will
likely fuel an increase in trade showers, with another frontal
remnant potentially introducing moisture into the trade flow as
well.

&&

.AVIATION...
A cold front passing well north of Hawaii will keep moderate to
fresh trade winds across the island today before winds strengthen
tonight due to high pressure building in from the northwest. The
trades will focus incoming low clouds and showers over windward
slopes resulting in brief mountain obscurations today, which could
increase in coverage late tonight. However, no AIRMETs are in effect
at this time. AIRMET Tango will likely be issued tonight or Monday
morning for leeward mountain turbulence as the trade winds
strengthen.

&&

.MARINE...
High pressure building north of the state tonight will bring an
increase in trade winds and will result in fresh to strong trades
through the first half of the week. Winds may near gale force Monday
night into Tuesday across the Alenuihaha Channel. After a slight
decrease of trade winds Wednesday night into Thursday, a 1035 mb
high building north of the state will bring widespread strong to
possibly gale force winds across the Hawaiian Waters Friday through
the weekend.

Forerunners from a new northwest swell will begin to fill in late
tonight and the swell is expected to steadily build through the day
Monday. Surf will likely reach high end advisory levels Monday night
as the swell peaks. Another advisory level northwest swell is
expected to steadily build Wednesday night. The combination of
strong trade winds and large northwest swells will bring widespread
Small Craft Advisory conditions on Monday and will likely persist
through most of the week.

With the expected boost in trades throughout the new work week, surf
along east facing shores will be on the rise. Surf will likely reach
the High Surf Advisory (HSA) criteria of 8 feet for east facing
shores later in the week with the stronger surge of trade winds. It
should be noted that waters and ocean conditions will be very rough
and choppy through most of the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

DISCUSSION...Birchard
AVIATION...Foster
MARINE...Kino