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WindWSW 11 mph
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Hawaiian Islands Synoptic Discussion and Guidance

678
FXHW60 PHFO 201953
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
953 AM HST Mon Feb 20 2017

.SYNOPSIS...
Areas of high pressure will reside north of the area through the
week. The result will be for a breezy trade wind weather pattern
across the state. Clouds and passing light showers will favor
windward and mauka areas while most leeward locations will
generally be dry. Winds are expected to diminish over the weekend
as an area of low pressure develops northwest of the area.

&&

.DISCUSSION...
Breezy to locally wind trade wind weather can be expected over
the next several days as areas of high pressure reside north of
the state. One area of high pressure will be passing by from west
to east today through Tuesday. A front will pass by well north of
the area which may result in a brief downtick in winds speeds on
Tuesday. However another high will quickly build in north
northwest of the area by Wednesday with a slight uptick in winds
expected.

The airmass over the area is rather dry and stable. However
moisture embedded in the trades is providing for clouds and some
passing light showers to fall over windward and mauka areas. This
weather pattern is expected to continue for the next several days
with shower activity highly dependent on incoming moisture
availability. Winds will begin to drop off later in the week as
the pressure gradient over the area relaxes just a bit.

As we head into early next week, global models indicate a mid
level trough of low pressure will develop to the north and
northwest of the area. This may cause for a less stable airmass to
be in place with an uptick in shower activity possible. There are
differences in the low level pattern with the GFS indicating us
remaining in a light to moderate trade wind environment with
moisture riding in on the trades, while the ECMWF has a lighter
wind field over the area with some moisture being drawn up from
the south over the area. Thus confidence on any real specifics in
the weather details is rather low in the long range forecast.

&&

.AVIATION...
A strong high pressure system located north of the Hawaiian Islands
will continue to produce strong northeast trade winds for the next
few days. A strong low level inversion will keep cloud ceilings at
or below 7000 feet. Mostly VFR conditions are expected with
scattered light showers along windward slopes.

AIRMET Tango in effect today for moderate turbulence over and
south through west of all islands.

&&

.MARINE...
Strong high pressure moving to about 525 nm north of Kauai will
keep strong to gale force trade winds in place today. An overnight
ASCAT pass detected winds just below gale force around the Big
Island, but given the limitations of the sensor and high
resolution model guidance, we have kept the gale warning going for
the Alenuihaha and Pailolo Channels and Maalaea Bay today. A Small
Craft Advisory (SCA) remains in place for the remaining waters.
The gale warning may need to be extended into tonight, but expect
the SCA to continue for most, if not all waters, into Tuesday.
Another area of high pressure will build north of the islands late
Tuesday and Wednesday, likely keeping SCA conditions in place over
most waters into Thursday. A steady decline in winds is expected
heading into the weekend.

Large combined seas comprised of a mix of north-northwest swell
and wind waves are producing high surf across north and some
exposed west facing shores, in addition to contributing to the
SCA. NOAA buoys to the northwest of the islands are registering
combined seas of 10 to 11 ft, and larger seas of about 17 ft have
been measured at buoys 51000 to the northeast of the islands.
While the largest seas will continue to pass east of the state,
expect the mix of longer period (13 to 14 seconds) and shorter
period wind waves to maintain high surf today then drop off
tonight and Tuesday.

A pair of long period swells from distant sources will produce
somewhat elevated surf along north and west facing shores later
this week, while rough, short period trade wind seas maintain surf
just below advisory levels along east facing shores through
Thursday. The first northwest swell is expected to arrive on
Wednesday and peak in the double overhead range Wednesday night
and Thursday. The second northwest swell will likely be larger and
may lead to advisory level surf Friday night and Saturday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui
Windward West-Maui Central Valley-Windward Haleakala-Big Island
North and East.

Wind Advisory until 6 PM HST this evening for Lanai-Kahoolawe-
South Big Island-Big Island North and East-Kohala.

Small Craft Advisory until 6 PM HST Tuesday 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-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

Gale Warning until 6 PM HST this evening for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel.

&&

$$

Synopsis/Discussion...Burke
Aviation...Bohlin
Marine...Wroe

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