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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 050122

Area Forecast Discussion
National Weather Service Honolulu HI
322 PM HST Sat Jul 4 2020

Light to moderate east-southeasterly trades will continue through
the holiday weekend. Showers will favor windward and mauka areas,
although scattered showers will also affect leeward and interior
areas at times. A more typical trade wind pattern will resume on
Monday, with showers favoring windward and mauka areas along with
the stray leeward spillover. This trade wind pattern will hold
through late next week, with breezy conditions expected Tuesday
into next weekend.


Currently at the surface, a 1030 mb high is centered around 1600
miles north of Honolulu, while a weak trough of low pressure is
located several hundred miles northeast of the state. The
resulting gradient is producing light to moderate east-
southeasterly trades across the island chain this afternoon.
Visible satellite imagery shows partly to mostly cloudy conditions
across the state, with radar imagery showing scattered showers, a
few of which are fairly heavy. Main short term concerns revolve
around rain chances and trade wind trends.

The gradient will remain disrupted from the high far north of the
islands during the next couple days due to the trough of low
pressure northeast of the state which will track steadily
westward. The trough should dampen out by Monday, allowing high
pressure to become more dominant, with the high then sliding
southward and closer to the islands Tuesday through late next
week. Light to moderate east-southeasterly winds should hold in
place through the remainder of the holiday weekend, with localized
sea and land breezes developing in the more sheltered leeward
areas. Moderate trades will then return through the day on Monday
and become breezy Tuesday through late next week.

Shower coverage should diminish this evening as daytime heating
is lost and a pocket of lower PW values moves over the islands.
Scattered windward showers will remain possible through the night
and during the morning hours Sunday, with isolated leeward showers
remaining possible mainly near the coast in the east-
southeasterly boundary layer flow. Scattered showers are expected
to continue to affect windward areas Sunday afternoon, with
scattered leeward/interior showers developing as a result of sea
breezes and daytime heating influences. Showers should diminish in
most leeward/interior areas Sunday evening, with scattered
showers continuing in windward locales. As trade winds become more
dominant on Monday, we should see a return of more typical trade
wind weather, featuring mainly windward/mauka showers and a few
leeward spillovers. This pattern appears to hold in place through
late next week.


An area of moist air associated with a low level trough has been
moving slowly west across the main Hawaiian Islands while a
trough aloft has been making the atmosphere a bit unstable. A
band of showery low clouds over the islands has partly broken up
since this afternoon and clouds and showers have diminished over
east sections of the smaller islands. The low level trough has
shifted the winds from south of due east, so more showers than
usual have been coming ashore in the Kau district of the Big
Island. Lines of showery low clouds coming off Molokai have been
moving over Oahu and enhancing showers there. AIRMET Sierra for
mountain obscuration is in effect for the Big Island and Oahu.
Mountain obscuration is likely to continue tonight and may affect
other islands. Drier are will be spreading west over the area
later tonight bringing higher cloud ceilings and fewer showers.


A surface trough west of Kauai has weakened the pressure gradient
over the state and will maintain light to moderate trades through
Sunday. As the surface trough shift further west, a ridge of high
pressure will strengthen far north of the state early next week.
This will cause the trade winds to gradually strengthen.
Therefore, Small Craft Advisory (SCA) conditions will likely
develop across the typically windier waters adjacent to the
islands of Maui County and the Big Island as early as Monday
night, and continue through mid-week.

Surf is expected to remain below the High Surf Advisory criteria
along all shorelines through early next week. Expect a mix of
small background swells from the southeast and south through next week.
A slightly larger south swell arriving late Wednesday is expected
to gradually build through Thursday. This may cause a slight
increase in surf along most south facing shores during the second
half of next week.

The weak trade wind regime will keep small surf along east facing
shores into early next week. As the trade winds strengthen,
expect choppy surf to increase along east facing shores from late
Tuesday through the end of next week. Surf along most north facing
shores will remain nearly flat for the foreseeable future.
However, small background easterly trade wind wrap and small
northwest swell energy may produce periods of tiny surf along some
north facing beaches and reefs.






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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