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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 180213

Area Forecast Discussion
National Weather Service Honolulu HI
413 PM HST Fri Jan 17 2020

High pressure building north of the state will bring a breezy and
dry trade wind pattern over the weekend. Some showers will
continue to impact windward and mauka areas especially around Maui
County and the Big Island from time to time, but they should
remain light in intensity. Overall, a much drier weather pattern
is expected through the first half of next week with trade winds
decreasing on Tuesday and possibly becoming variable by Wednesday.


A cold front has made its way through the state today and is
dissipating northeast of the Big Island. A much drier airmass has
moved in across the western half of the state and the 00Z
sounding from Lihue came in with precipitable water values of 0.62
inches. This is well below normal and any showers overnight
tonight should be more like a drizzle over Kauai. As we shift
further east, lingering moisture from the remnants of the front
continues to produce scattered showers across windward and mauka
locations from Oahu to the Big Island this afternoon. Looking
upstream on satellite, a train of light to moderate showers is
located upstream of Maui County and the Big Island. So for
tonight, scattered showers will likely impact these areas and may
cause some minor ponding and rises in streams across windward and
mauka areas.

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 especially around Maui County 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
showers on the lighter side.


A front will weaken near the Big Island tonight, while breezy
north northeast winds will continue across the rest of the state.
AIRMET Tango is posted for moderate turbulence for leeward Kauai,
Oahu and Molokai due to the stronger winds and a stable

AIRMET Sierra is posted for tempo mountain obscurations across
windward and northern sections of the islands this afternoon.
AIRMET Sierra will likely end later on tonight for the smaller
islands, but continue across windward Big Island. VFR conditions
will prevail across leeward sides of the islands.


High pressure north of area is producing strong breezy north to
northeasterly winds over the Hawaiian Islands. High Surf Advisory
has been issued for Niihau and Kauai through tonight. A Small
Craft Advisory (SCA) has also been issued for most areas.

Saturday through Monday, 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 a
progressive pattern across the northern Pacific continues and a
couple of fronts pass to the north.

Expect rough conditions along exposed north shores due to short
wave periods (10-11s) and strong onshore winds. Kauai north shore
is seeing the highest surf height of 8 to 15 ft thus a High Surf
Advisory was issued through tonight. A long period north to
northwest swell expected Sunday will likely drive surf heights up
to advisory levels for north and west facing shores. This will
hold through Monday before lowering Tuesday.

Surf along east facing shores will remain small due to the lack
of strong trades locally and upstream. However, easterly
locations with a northerly exposure may trend up tonight through
the weekend as the strong northerly winds and northerly swell

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, advisory level surf can be
anticipated by 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.


High Surf Advisory until 6 AM HST Saturday for Niihau-Kauai
Windward-Kauai Leeward.

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.




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