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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 190631

Area Forecast Discussion
National Weather Service Honolulu HI
831 PM HST Fri Jan 18 2019

Moderate to breezy trades will return for a brief period Saturday,
then shift toward the south and weaken Saturday night through Monday
as another cold front approaches. This front is expected to stall
and weaken near or just north of Kauai late Monday through
Tuesday. Increasing moisture combined with this front stalling
nearby will support the best rainfall chances setting up over
Kauai through the first half of the week, especially through the
afternoon hours as sea breezes setup. Elsewhere, drier conditions
and light winds are expected.


The evening satellite imagery showed a lingering moisture axis
across the central islands that was supporting a band of low clouds
and a few windward showers. Drier conditions were shown over Kauai
and much of the Big Island. This setup combined with light trades
that have begun to fill back in across the state will support the
best rainfall chances setting up over the windward locations of Maui
County and Oahu overnight into Saturday. Trades are forecast to
increase into the moderate to breezy category through the day
Saturday as high pressure builds to the north.

The progressive pattern across the northern Pacific will continue
Sunday through the upcoming week featuring a series of cold fronts
passing to the north and the subtropical ridge shifting southward
over the state. The first front in the series will approach and
stall near or just north of Kauai Sunday night through the first
half of the week. The local winds will shift toward the south and
weaken ahead of this approaching front through the day Sunday.
Increasing moisture combined with this front stalling near the
western end of the state will support the best rainfall chances over
and around Kauai through the first half of the week, especially
through the afternoon hours as sea breezes setup.

Drier conditions along with light background trade wind flow are
expected to hold across the eastern end of the island chain next
week, with the exception being across leeward and interior areas
where daytime sea breezes and overnight land breezes setup. Any
showers that do develop will favor windward areas, except through
the afternoon hours across leeward locations where clouds and a
few showers associated with sea breezes will become a possibility
through the afternoons.


Remnant moisture from a dissipated front lingers across the
windward areas of the smaller islands this evening, and is
expected to remain in this general area for the rest of the night.
The base of these stable low clouds is 35 hundred feet, thus
negating the need for AIRMET Sierra. Tops of the clouds are around
6 to 7k feet. Isolated patches of light rain or drizzle with no
restriction to vis, can be expected with these clouds. There will
be brief periods or isolated areas of MVFR ceilings overnight,
with 25 hundred foot bases. Lee areas look even better for all of
the smaller islands and all of the Big Island tonight, with
scattered low clouds expected.

Trade winds are currently light. They are rather shallow as well,
up to 6 to 7k feet. Trades are expected to strengthen to moderate
speeds by 202200 UTC, at which point, we will determine the need
of AIRMET Tango. But Tango is not needed overnight.

The current northeast winds are supplied by a surface high that
will be passing north of the islands tonight, heading toward the
east. By this time tomorrow, the high will be far away from the
islands. In response, these winds will be veering to the east on
Saturday, becoming slightly south of east over on Kauai by
Saturday evening. Further veering of the winds will come Saturday


A slow-moving front that had been near Maui has dissipated.

Otherwise, as an area of high pressure passes north of the state
tonight, trade winds will increase, then rise to fresh to locally
strong levels Saturday. This may produce Small Craft Advisory
(SCA) winds across the typically windy waters around the Big
Island and Maui. Winds will ease slightly and begin to veer out of
the southeast Saturday night as a surface ridge moves toward the
islands in response to an approaching front. On Sunday and early
next week, the ridge will stall near Oahu, leading to southerly
winds over the western half of the state and southeasterly winds
near the Big Island and Maui.

A moderate and relatively short-period north-northwest swell
peaked earlier today. The SCA for hazardous seas around Kauai and
waters north of Oahu has been cancelled, though seas remain
somewhat elevated. This swell will gradually decline tonight
through the weekend, followed by a series of overlapping northwest
swells next week. The first of these swells will arrive Monday,
with surf remaining below advisory levels. The next swell will
arrive Tuesday and result in surf well above advisory levels for
north and west facing shores Tuesday night and Wednesday. As this
swell declines Thursday, a large reinforcing northwest will
build, possibly leading to warning level surf late Thursday and

As trade winds pick up, a slight increase in short-period surf
will occur along east facing shores. Even though winds locally
will remain southerly or weak easterly, stronger trade winds well
east of the state may produce a bump in east shore surf during
the middle of next week.






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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