Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 192031
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1031 AM HST Fri Jan 19 2018

.SYNOPSIS...
A strong high northeast of the area is moving away to the east. A
ridge extending southwest from the high will remain north of the
islands. The strong trade winds over the islands have subsided,
and will continue to weaken as the high moves farther away. A
band of showery low clouds along a dissipating front will remain
nearly stationary over the islands, keeping windward areas rather
wet through early next week. A new front approaching from the
northwest will weaken the ridge and make the atmosphere more moist
and less stable. Daytime sea breezes and nighttime land breezes
will become more widespread early next week with afternoon clouds
and showers possible over interior areas. Trade winds and windward
showers will return by the middle of next week.

&&

.DISCUSSION...
A strong 1036 mb high about 1200 miles north of Oahu is forecast
to move east around 20 mph. The pressure gradient south of the
high has been producing strong easterly trade winds over the
islands. With the high now farther away, the pressure gradient has
weakened. Winds around the islands have subsided, and will
continue to weaken through the weekend.

An east to west band of showery low clouds along a dissipating
stationary front continues to move over the islands in the trade
winds and keep windward areas quite rainy through tonight.

A trough aloft and a cold front will move toward the islands from
the northwest over the weekend. As the front approaches, the winds
over the islands will weaken further and veer out of the
southeast near Kauai and Oahu. The old frontal band may shift
north of Kauai and Oahu, but will likely remain over the Big
Island. As the trough aloft moves closer and the atmosphere
becomes more unstable, heavier showers and snow over the summits
are possible on the Big Island early next week.

The front is forecast to stall northwest of the islands on
Tuesday. The surface ridge will rebuild north of the islands. The
atmosphere will become more stable and trade winds will strengthen
again around the middle of next week.

Late next week another trough aloft and front may approach the
islands from the northwest.

&&

.AVIATION...
AIRMET Tango is in effect today for tempo moderate turbulence
leeward of all islands due to fresh to strong trade winds. AIRMET
TANGO is also in effect for strong surface winds across leeward
Kohala. Trade winds are expected to weaken tonight into Saturday
morning, and we will likely cancel this AIRMET once winds taper
off.

AIRMET Sierra is in effect for tempo mountain obscurations across
windward sections of Kauai, Oahu, Molokai, Maui and the Big
Island. This is due to passing clouds and showers associated with
a weakening front pushing onto these islands with the trade wind
flow. This AIRMET is expected to continue through the rest of the
day, and possibly into tonight.

No other AIRMETs are anticipated at this time.

&&

.MARINE...
Trade winds have started to weaken area-wide this morning as the
surface high north of the state moves east. Therefore, the Gale
Warning for selected waters around Maui County and the Big Island
has been downgraded to a Small Craft Advisory (SCA). The SCA has
been canceled for the Oahu and Maui leeward waters. The decreasing
winds will also likely cause the waters south of the Big Island
to drop out of the SCA by tonight. However, due to elevated seas
generated east of the Big Island, the SCA will persist over most
of the windward waters into Saturday. Seas are expected to subside
below the advisory level of 10 feet Sunday night, allowing for
cancellation of the SCA at that time. The High Surf Advisory (HSA)
for east facing shores has been extended through 6 am HST
Saturday due to the aforementioned seas east of the state.

Surf will remain below advisory levels for the remaining shores
through this weekend. A small northwest swell (330 degrees) is
expected arrive Saturday night, and be reinforced with a moderate
west-northwest (300 degrees) swell Sunday night through Monday
that will peak Monday night and gradually decline through
Wednesday. This second swell may warrant an HSA for the north
facing shores of some of the smaller islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 600 PM Friday for Kohala.

High Surf Advisory until 600 AM Saturday for east facing shores
of Kauai, Oahu, Molokai, Maui and the Big Island of Hawaii.

Small Craft Advisory until 600 AM Saturday for all waters except
for leeward Kauai, leeward Oahu and leeward Maui County waters.

&&

$$DISCUSSION...Donaldson
AVIATION...Almanza/Foster
MARINE...TS



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