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Hawaiian Islands Synoptic Discussion and Guidance

482
FXHW60 PHFO 171957
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
957 AM HST Fri Jan 17 2020

.SYNOPSIS...
A dissipating cold front is currently moving through Maui and
will be making its way to the Big Island late this afternoon.
Breezy northerly winds and showers are expected behind the front
as high pressure builds north of the state. Cool and drier
weather is expected over the weekend across most of the state,
with the exception of the windward Big Island where showers will
continue to move in from time to time. Overall, a much drier
weather pattern is expected for the first half of next week.

&&

.DISCUSSION...
A dissipating cold front is currently moving through Maui and
will be making its way to the Big Island late this afternoon.
Latest radar and satellite imagery is showing a line of light to
moderate showers over east Maui just ahead of the front and this
line should be weakening and moving into the Big Island this
afternoon. Behind the front, we have breezy northerly winds and
showers passing through state. Looking upstream on satellite,
a train of showers looks to be headed toward the eastern half of
the state tonight, which could bring frequent showers to the
windward and mauka areas of Maui and the Big Island. Due to the
relatively stable atmosphere by tonight, most of these showers
should be moderate in intensity.

Over the weekend, high pressure will continue to build north of
the state and will lead to a breezy and dry trade wind pattern
across most of the state. Lingering moisture from the front will
continue to bring showers from time to time over windward and
mauka areas of Maui and the Big Island. Dewpoint temperatures will
be down in the low 60s and may make the air feel slightly cooler
than normal.

In the long term, a ridge of high pressure will persist north of
the state through Monday and gradually shift southeast and
towards the state Tuesday into Wednesday. This will lead to the
trade winds weakening with possible sea breezes developing by
Tuesday afternoon across select areas. Precipitable water values
will remain drier than normal next week, which should keep the
weather on the drier side.

&&

.AVIATION...
A weakening front will move southeast across the state today with
strengthening north northeast winds pushing in drier air behind.
AIRMET Sierra is posted for tempo mountain obscurations across
north through east sections of the smaller islands this morning,
which will likely spread to windward portions of the Big Island
this afternoon and begin to decrease over the western end of the
state by late afternoon or evening. Meanwhile, VFR conditions
will prevail across leeward sides of the islands today.

AIRMET Tango is posted for moderate turbulence for leeward Kauai
and Oahu for the stronger winds and stable atmosphere moves in
bringing mountain wave turbulence. This will also progress
eastward today and tonight in the wake of the front. AIRMET Tango
is also in effect through 22Z between 150 and FL250 as a weak
upper trough moves across the area, and will likely expire at that
time.

&&

.MARINE...
High pressure north of area is producing strong breezy
north to northeasterly winds over the smaller islands this
morning following a weakening front currently over Maui. Small
Craft Advisory (SCA) has been expanded down the island chain due
to a combination of winds and seas expected to ramp up through the
day as the front dissipates.

Saturday through Monday, the winds will hold in the fresh to
locally strong category while gradually shifting out of a more
easterly trade wind direction. Light and variable winds will
become a possibility Tuesday through the second half of next week
as the progressive pattern across the northern Pacific continues
and a couple of fronts pass to the north.

Surf along east facing shores will remain small due to the lack
of strong trades locally and upstream. Easterly locations with a
northerly exposure, however, may trend up today through the
weekend as the strong northerly winds and northerly swell build
down the island chain.

Surf along north facing shores will trend up quickly today as a
medium period north swell fills in. Expect rough conditions along
exposed shores due to the expected short wave periods (10-11s)
and strong onshore winds. Heights may approach advisory levels up
north if the seas surge higher than predicted tonight, which is
typical for these patterns. A long-period north-northwest swell
expected Sunday will likely drive surf heights up to advisory
levels by Sunday night for north and west facing shores. This will
hold through Monday before lowering Tuesday.

For the extended, guidance shows a pattern shift across the
northern Pacific featuring two gale to storm force systems racing
eastward from Japan to the Date Line over the weekend and again
early next week. If this materializes, a large long-period
northwest swell will reach Hawaii Wednesday through the second
half of the week.

Surf along south facing shores will remain small through early
next week with mainly small background southwest swells expected.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Kino/Powell
AVIATION...Foster
MARINE...Almanza/Morrison

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



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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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