Gale Warning 1, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
918 AM HST Sun Jan 5 2020

.SYNOPSIS...
A rather breezy to locally windy trade wind weather pattern is in
store for the this week due to high pressure north of the area.
Moisture embedded in the trades will provide for passing windward
and mauka showers over the next few days with the trades sufficiently
strong enough to blow some brief passing showers over to leeward
areas at times. A wetter trade wind pattern is setting up for the
second half of the week as an upper low moves over the area from
the east.

&&

.DISCUSSION...
A 1040 MB high is centered far northeast of the state. This
places the islands in a breezy to locally windy trade wind
environment. Meanwhile an upper level low is centered a few
hundred miles east of the Big Island. Moisture embedded in the
trades is providing for some passing showers over windward and
mauka areas with the trades sufficiently strong enough to blow
some of these showers over to leeward areas at times. We expect
this general weather pattern to persist through the day.

Surface observations as well as model guidance indicates rather
strong winds will occur for the next few days over the Big Island
summits. Thus a Wind Advisory has been issued and and is expected
to remain in effect through the day Tuesday.

The surface high will drift slowly westward over the next few days
keeping the area in a breezy to locally windy trade wind regime
into the middle of the week. Clouds and passing showers will
continue to favor windward and mauka areas with some brief passing
showers also possible over some leeward locations.

The upper low is forecast to remain stationary for a few days
then gradually drift westward closer to the state by Wednesday or
Thursday. This will cause the airmass to become less stable. This
along with an expected increase in low level moisture moving in
the trades will cause for an increase in shower activity
especially over windward and mauka areas. Thus a rather wet and
windy trade wind pattern is shaping up for later this week and on
into next weekend.

&&

.AVIATION...
Strong high pressure northeast of Hawaii will continue to produce
breezy trade winds across the state for the next several days.
AIRMET Tango for low level turbulence remains in effect and will
continue. Clouds and showers will favor north and east facing
slopes and coasts, with some spillover showers leeward at times.
AIRMET Sierra for mountain obscuration will remain in effect for
windward areas of Oahu, Maui, and the Big Island into this afternoon.
Conditions are expected to improve later this afternoon as moisture
in the area decreases.

&&

.MARINE...
Strong to gale-force easterly trades are expected through the
week as strong high pressure remains anchored north to northeast
of the state. Gales are expected in the typical windier areas,
especially the Pailolo and Alenuihaha Channels where a Gale Watch
is in effect beginning tonight.

Seas exposed to the trades will respond and hold around the
advisory level (10 ft) through Tuesday. The gradient between high
pressure (1040 mb) to the northeast and a weak surface trough
forecast to develop east of the state will tighten over a large
area through the first half of the week. Wave model guidance
reflects this and depicts seas building locally into the 10 to 15
ft range Tuesday through the end of the week as the surface trough
approaches and moves into the area.

Surf along exposed east facing shores will remain rough, likely near
or just below the advisory level through Monday. An upward trend is
expected Tuesday through midweek as the previously discussed area of
strong winds and large seas moves into the area. Although confidence
remains low this far out, given the wave model differences, warning-
level surf can't be ruled out between Wednesday and Friday.

A combination of large seas, potentially warning-level surf, strong
onshore winds and water levels running around half of a foot above
predicted will support significant beach erosion and wave runup over
areas that typically remain dry along east facing shores, mainly
through the second half of the week, when peak high tides and
surf will be higher.

Surf along north facing shores will trend down today as the small
north swell eases. A small mid-period northwest swell will fill
in by Monday, then hold through Monday night. A small long- period
northwest swell is expected Tuesday through midweek. An upward
trend is expected through the second half of the week as a broad
storm-force low sets up over the far northwest Pacific (near
Kamchatka Peninsula) Monday through Tuesday. Surf may near or
reach advisory levels for north and west facing shores Friday
night into Saturday if this scenario evolves.

Surf along south facing shores will remain nearly flat through
Monday. A couple of background south to southwest swells expected
Tuesday and late Friday through next weekend should be enough to
keep the surf above flat levels.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Tuesday for Big Island Summits.

Small Craft Advisory until 6 PM HST Thursday 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-Maalaea Bay-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.

Gale Watch from 6 PM HST this evening through Tuesday afternoon
for Pailolo Channel-Alenuihaha Channel.

Small Craft Advisory until 6 PM HST this evening for Pailolo
Channel-Alenuihaha Channel.

&&

DISCUSSION...Burke
AVIATION...TS
MARINE...Kino