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Forecast Discussion for Honolulu, HI

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000
FXHW60 PHFO 220129
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
329 PM HST Sun Oct 21 2018

.SYNOPSIS...
An upper trough near the Big Island will continue moving slowly
eastward today. Drier weather will spread across the entire state
tonight as trade winds increase slightly. Trade showers will favor
windward and mountain areas, and will occur mostly during
overnight and early morning hours. A wetter trade wind pattern may
develop by midweek as deeper tropical moisture moves into the
state from the southeast.

&&

.DISCUSSION...
There is no change in forecast philosophy from this morning.
Water vapor loop shows an upper trough axis moving slowly eastward
across the Big Island this afternoon. Moderate trade flow has
returned at the surface statewide, with little in the way of
clouds and showers noted immediately upwind from the islands.
Afternoon soundings show continued drying from 12 and 24 hours
ago, with PW down to 1.44 inches at Hilo and down to 1.17 inches
at Lihue. Furthermore, the Lihue sounding showed development of an
inversion near 5500 feet as well as positive LI values,
indicating a stable airmass there.

The upper trough will continue to move slowly eastward, with a
drier airmass continuing to filter across Maui County and the Big
Island tonight. Like it did today today, daytime heating will
increase cloud cover across interior areas Sunday afternoon, and
possibly trigger deep convection, especially on the Big island. A
few heavier showers may still be possible there, but we don`t
expect thunderstorms or an elevated risk of widespread flash
flooding.

Trade winds will increase slightly through Monday, while an upper
ridge building in from the west provides a more stable atmosphere
over the state. Rather typical trade wind weather will continue
through Tuesday, with passing showers favoring windward and mauka
areas. A wetter trade wind pattern may develop beginning Tuesday
night into Wednesday, when models depict an area of greater
moisture spreading over the state from the east. Longer range
guidance suggests that the wetter trades may then persist through
the remainder of the work week.

&&

.AVIATION...
An upper trough will slowly pass across the Big Island tonight as
high pressure builds in from the northwest. Expect VFR conditions
to dominate at the terminals. Also expect slightly stronger trade
wind flow across the state as high pressure builds in and brings
more stable conditions from west to east. Passing trade wind
showers over the next few days will favor windward and mountain
areas in a moderate trade wind weather pattern.

No AIRMETs are in effect.

&&

.MARINE...
Trade winds will continue through the week, due to a high pressure
ridge north of the islands. The pressure gradient over the area
will increase heading into the middle of the week as a weak trough
passes south of the islands. This will result in an uptick in wind
speeds, with Small Craft Advisory (SCA) level winds anticipated
Tuesday night through Wednesday night for the typically windier
areas near Maui and the Big Island. Seas are expected to remain
below SCA levels through the period.

The current south swell is holding, with a slow decline expected
over the next 24 hours. The current High Surf Advisory for south
facing shores continues through 6pm Monday. Additional south
swells through the week and weekend will keep surf elevated along
south facing shores, with the possibility of advisory level surf
during the second half of the week.

No other advisory level surf is anticipated through the upcoming
weekend. A moderate north-northwest swell is expected to reach
the islands Monday night and Tuesday, peaking Tuesday night or
Wednesday below advisory levels, and then slowly declining
through the end of the work week. A new north swell looks to be
coming in at the end of next weekend.

See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai-
Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central Valley-
Windward Haleakala-Leeward Haleakala-Kona-South Big Island-Big
Island North and East-Kohala.

&&

$$

DISCUSSION...Powell
AVIATION...Burke
MARINE...M Ballard

Previous Forecast Discussions may be found at
NWS Honolulu, HI (HFO) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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