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Hawaiian Islands Synoptic Discussion and Guidance

792
FXHW60 PHFO 230645
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
845 PM HST Wed Jan 22 2020

.SYNOPSIS...
Variable winds in a stable land and sea breeze weather pattern
will continue over most of the islands through Friday afternoon.
Expect low clouds developing with isolated light interior showers
possible each afternoon followed by overnight clearing across most
islands. One exception will occur over the southeast slopes of
the Big Island where a slight increase in clouds and showers
remains in the forecast through Friday. A weak front stalling
near Kauai on Friday afternoon will increase clouds and showers
over the Garden Isle through Saturday. Moderate trade winds will
return from Friday afternoon through the weekend along with
slight increases to windward and mountain showers. Winds will
decrease and veer southeasterly in a dry land and sea breeze
pattern for the first half of next week.

&&

.DISCUSSION...
The weather picture this evening shows the Hawaiian Islands under
the southwestern edge of the subtropical ridge with frontal
boundary north of the islands heading east, and another cold
front approaching the state from the northwest direction. Dry and
stable weather conditions under the ridge are forecast with
variable winds allowing local scale land and sea breezes to
develop over most islands through Friday. Dry moisture levels in
the atmosphere will produce cooler than normal low temperatures
each night.

Friday through Sunday, the weather pattern changes a bit as a
weakening cold front moves into Kauai and Niihau. This front will
reach Kauai by Friday afternoon just as the forward motion along
the frontal band stalls out. Expect increasing clouds and showers
for both islands from Friday into Saturday. Trade winds will bleed
out ahead of the stalling frontal band with trades slowly spreading
eastward to all islands through Saturday morning. Clouds and
isolated to scattered showers over windward and mauka areas will
also return with these moderate trades lasting through the
weekend. East to southeast trade winds on Sunday will push the
clouds and showers along the frontal boundary towards the
northwest away from Kauai County with improving weather
conditions in the forecast from Saturday night onward.

Monday through Wednesday, trade winds will veer towards the
southeast direction with a subtropical ridge axis anchored roughly
400 miles north of the island chain. Light southeasterly winds
will allow a return to land and sea breezes over the islands with
a slight increase to clouds and showers along the southeastern
slopes of the Big Island. This drier weather pattern will bring
sunny skies back to the islands through the middle of next week.
Additional high clouds moving into the region next week will
improve sunrise and sunset colors from Wednesday onward.

&&

.AVIATION...
A high pressure ridge will remain over the state for the next 24
hours and allow for a light and variable wind pattern. Relatively
dry air in place should keep precipitation chances low. By
Thursday afternoon, expect weak sea breeze development along
coastal areas. Otherwise, light variable winds and dry conditions
will prevail once again.

&&

.MARINE...
Light and variable winds will continue through early Friday, then
shift out of the north to northeast and increase into the moderate
to fresh category late Friday as a front passes north of the area.
Fresh to locally strong easterly trades are expected for a brief
period over the weekend before trending back down by early next week
as a series of fronts pass to the north. Although seas may briefly
drop below the Small Craft Advisory (SCA) level (10 ft) Thursday
night through Friday as the large northwest swell subsides, advisory-
level conditions will return Friday night through the weekend due to
a combination of winds and seas.

Surf along north and west facing shores will remain up through next
week due a series of large northwest swells evolving from the
progressive pattern over the northern Pacific. The current swell
building down the island chain has peaked at the northwest offshore
buoys (15 ft 17 sec) this afternoon, which will correspond to an
overnight peak locally. Although a gradual downward trend will begin
through the day Thursday, surf will hold above warning levels for
exposed north and west facing shores. The downward trend will be
short-lived due to another large northwest swell arriving Friday
night into Saturday from a large area of gale- to storm-force winds
that has setup within the 300-320 directional band relative to the
islands over the northwest Pacific. Surf will respond and return
warning levels Saturday through Sunday. As this swell eases into
early next week, advisory-level surf may hold through late Monday.
Another large northwest swell will be possible by next Wednesday as
a gale develops over the far northwest Pacific this weekend.

Surf along exposed east facing shores will remain small through the
period due to the lack of persistent trades locally and upstream
across the eastern Pacific.

Surf along south facing shores will remain small through next week.
A couple of background south swells expected over the weekend and
next Tuesday should be enough to keep things from going flat.

&&

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

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-Big Island Windward Waters-Big Island
Leeward Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Gibbs

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office