Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 172000

Area Forecast Discussion
National Weather Service Honolulu HI
1000 AM HST Tue Oct 17 2017

High pressure north of Hawaii will keep a windy trade wind
pattern in place through much of the work week, with the trades
trending down slightly Friday and weakening further over the
weekend. Clouds and showers will favor windward and mauka areas
through the period, but showers will reach leeward areas from
time to time as well due to the strength of the trades.


Windy conditions will continue to be the main weather player
across the state over the rest of the work week. High pressure
around 1030-1034 mb expected to remain to the north of the state
will result in pressure gradient supportive of strong winds,
locally to wind advisory strength in the windiest areas around
Maui County and the Big Island. See the latest public information
statement for details on peak wind gusts around the state. Along
with the winds, pockets of showers riding along in the trades will
continue to pass over the state. Strength of the wind flow, and
precipitable waters below normal, will keep rain totals generally
on the light side for both windward and leeward areas.

The pattern is expected to shift as we go into the weekend as the
ridge to the north shifts eastward and is replaced by a trough
which carves out from the mid latitude westerlies somewhere to the
north or northwest of the state. GFS ensemble spread is fairly
small for this far out, and ECMWF in good agreement with GFS, thus
the forecast trending towards lighter trade winds Saturday, then
light southeasterly flow Sunday and Monday, looks good. Most areas
should be fairly dry Saturday, however an upper level trough looks
poised to move in from the east on Sunday which will provide more
instability and potential for afternoon and evening showers,
especially interior and leeward areas on Sunday and Monday.
Details will become more clear and the forecast refined over the
coming days for the early part of next week, but there is a threat
of unsettled weather in the state during that time period.


High pressure north of the area will continue to deliver strong
trade winds over the state today. AIRMET TANGO for low level
turbulence is posted across the island chain. Scattered showers
riding in on the trade wind flow will stream over the islands,
with some showers being intense but brief and introducing periods
of MVFR to isol IFR CIGS/VIS. Widespread shower anchoring along
the mountains is not expected, nor is AIRMET SIERRA for mountain

AIRMET TANGO for upper level turbulence is also posted between
FL210 and FL280 from Molokai through the Big Island. This will
continue to be evaluated as the tail-end of an upper level moves
away from the state.


Very strong and gusty trade winds will persist through mid-week
due to a strong surface high far north of the main Hawaiian
Islands. This high will be replaced by another strong high late
Wednesday, continuing the gusty trades through Friday. The strong
to gale-force trade winds are also producing elevated rough seas
around the islands. A Gale Warning is posted for the Pailolo and
Alenuihaha channels through Thursday afternoon, while a Small
Craft Advisory (SCA) remains in effect across the remaining
Hawaiian waters through the same time. Trade wind speeds are
expected to diminish slightly by Friday as the high starts to
weaken and move east, with winds and seas likely dropping below
SCA criteria this weekend.

Elevated rough waves will continue to produce dangerous surf
conditions along most east facing shores across the state. Therefore,
a High Surf Advisory remains in effect through Wednesday afternoon.
Since the trade winds will continue to be strong, this advisory
will likely be extended through Thursday.

A High Surf Advisory remains in effect for south facing shores of
all islands through this afternoon. The south swell responsible
for this elevated surf is expected to slowly diminish tonight
through Wednesday. Small southwest and south-southwest swells
arriving this weekend will produce small background surf along
south facing shores.

The current small north-northwest swell is expected to gradually
subside through Wednesday. A long-period north-northwest swell
is expected to arrive Thursday and peak Friday. This swell will likely
produce moderate-sized surf (below the High Surf Advisory
threshold) along most north facing shores, as well as along some
west facing shores of the smaller islands. A slightly larger
northwest swell may arrive late Sunday, and continue into early
next week.

See the Collaborative Nearshore Swell and Wind Forecast (SRDHFO), for
more detailed information regarding the sources of these swells.


High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Oahu South Shore-Waianae Coast-Molokai Leeward-Lanai
Makai-Kahoolawe-Maui Leeward West-Maui Central Valley-Leeward

High Surf Advisory until 6 PM HST Wednesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 10 PM HST this evening for Lanai-Kahoolawe-
Big Island North and East-Kohala.

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Maalaea Bay-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.

Gale Warning until 6 AM HST Thursday for Pailolo Channel-
Alenuihaha Channel.



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