Current Conditions
Temp2.7 C
RH43 %
WindNNE 4 mph
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 170207

Area Forecast Discussion
National Weather Service Honolulu HI
407 PM HST Tue Oct 16 2018

Moderate trades will slowly weaken through Friday, then strengthen
again on Saturday. Remnants of a front will linger near the Big
Island for the next few days. A trough aloft will bring somewhat
unstable conditions around the Big Island before moving away late
this week. Drier weather will persist for the western half of the
state this week.


Water vapor imagery shows a trough aloft over the western end of
the state. A few high clouds are passing over the Big Island along
the subtropical jet on the eastern flank of the trough. The
trough aloft is also making the atmosphere less stable over the
Big Island and isolated thunderstorms have popped up along the Kau
District this afternoon.

At the low levels of the atmosphere, a 1021 mb high about 900
miles north of Kauai near 35N 156W is moving east at 20 mph. The
high is driving moderate trade winds across the state. Visible
satellite shows showery low clouds, the remnants of a frontal
band, extend upstream of Maui and the Big Island towards the east
northeast. The trades are pushing these clouds and scattered showers
across the windward slopes of both islands this afternoon. Fewer
clouds and showers are tracking in with the trade winds across
Molokai, Oahu and Kauai.

The current weather pattern will remain unchanged through Wednesday
as the remnant frontal clouds and upper trough remain in the same
position. By Wednesday night, the high to the north begins to
weaken and the trades will slowly taper off to gentle breezes by
Friday. The trough aloft will slowly begin to move away to the
northeast of the state Thursday and Friday, while the old frontal
band shifts east of the Big Island resulting in a gradual drying
trend for the windward slopes of Maui and the Big Island during
the second half of the week. The trade winds are forecast to
strengthen to moderate breezes again Saturday as another high
builds in from the northwest.


Moderate to fresh trade wind flow will continue tonight. These
trade winds have carried the remnants of an old frontal boundary
towards the islands. Expect shower activity to be focused along
Windward slopes and coasts, especially those of the Big Island.
Ceilings have risen slightly this afternoon, but are expected to
drop again overnight. Occasional MVFR ceilings across Windward Big
Island will likely become widespread by late evening. AIRMET
Sierra for mountain obscuration will remain in effect for the
north and east facing slopes of the Big Island. Sierra may need to
be expanded to include eastern Maui late tonight. Elsewhere,
across the remaining smaller islands, isolated MVFR ceilings and
visibilities are to be expected in passing showers, but VFR
conditions will predominate.

Also, AIRMET Tango for moderate upper-level turbulence remains in
effect over the island chain between FL280 and FL400 in
association with a deep trough aloft passing close to the
islands. Conditions are expected to end by this evening.


The current north-northwest swell continues to be on the rise this
afternoon. A surge this morning at the near shore buoys was short
lived, with the buoys quickly returning to the expected forecast
rise. The swell is still rising at buoys 51001 and 51101 and is
expected to peak there within the next few hours. This remains on
track with the last couple model runs. The High Surf Advisory
(HSA) remains in effect for north and some west facing shores of
the smaller islands. Will continue to monitor should the swell
peak higher requiring a warning, or if enough energy reaches the
Big Island to require an advisory there. At this time, still looks
like the Big Island will peak just below advisory levels.

The swell is producing seas in excess of 10 feet over some
waters, and combined with moderate to locally fresh trades, the
Small Craft Advisory (SCA) remains in place for all waters except
the leeward Maui County and leeward and southeast Big Island
waters. The SCA and HSA are both in effect until 6pm Wednesday,
but they may need to be extended depending on how the event pans
out. Trades are expected to ease during the second half of the

A smaller north-northwest swell is expected to arrive this
weekend, but is expected to remain below advisory levels. Surf
along south facing shores will remain elevated overnight, but
remain below advisory levels, and then trend down Wednesday. A
new south swell is expected to arrive Friday, and peak Saturday
into Sunday at high end advisory or low end warning levels. See
the latest collaborative surf discussion (SRDHFO) for more


High Surf Advisory until 6 PM HST Wednesday for all coastal
waters except Maui Leeward Waters, Big Island Waters and Big
Island Southeast Waters.

Small Craft Advisory until 6 PM HST Wednesday for north and west
facing shores of Niihau, Kauai, Oahu and Molokai and north facing
shores of Maui.



MARINE...M Ballard

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