Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 250635
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
835 PM HST Fri Nov 24 2017

.SYNOPSIS...
High pressure north of the State will keep strong trades over the
islands through this weekend and into early next week. Passing
showers will favor windward and mauka areas, with a few stray
showers expected to reach leeward areas of the smaller islands
from time to time. A wet trade wind weather pattern is expected
to develop on Sunday and continue through much of next week as
deep tropical moisture spreads into the area from the southeast.
The wettest conditions are expected over the eastern end of the
island chain.

&&

.DISCUSSION...
A 1037 mb high far north northwest of the main Hawaiian islands
continues to drive strong trade winds across local waters this
evening. Strong inversions aloft and less than an inch of PW put a
cap on cloud development and on total rainfall statewide today, a
trend that has lasted over the past few days. Radar shows
scattered moderate showers across the area, mainly across windward
portions of the islands and within the channels. Satellite loop
shows scattered to patchy broken low clouds across windward slopes
and across windward waters. Skies across leeward waters are
clearer.

Models show the high far to our north northwest will move
generally east southeastward through the weekend, keeping our
local pressure gradient steep enough to support strong trade winds
through the weekend. Wind Advisories remain in effect for Lanai
and for areas lee of the Kohala mountains on the Big Island
through Sunday, but may need to be expanded as conditions
warrant. Clouds and showers will favor windward and mauka areas.
Our airmass will gradually moisten over the weekend, with deep
moisture possibly reaching the Big Island on Sunday. Trade showers
will persist through the period, but may become more widespread
and heavier over the Big Island beginning Sunday afternoon.
Snowfall may occur at the Big Island Summits beginning Sunday
afternoon. However, we will not issue a Winter Storm Watch tonight
given the rather low forecast snow accumulations derived from our
QPF tool using an 8:1 snow-to-rainfall ratio. Our snow amount
grids have been adjusted downward accordingly. The need for a
Winter Storm Watch will be reassessed during the day Saturday, so
stay tuned.

We expect an overall wetter trade wind pattern from Sunday onward.
For the Big Island, the source will be the deep moisture mentioned
before. For the smaller islands, the source will be an old frontal
boundary expected to sag southward across the state Sunday night
through early next week. Moderate to breezy trade winds will
persist throughout, becoming locally windy at times.

&&

.AVIATION...
Strong trade winds are expected to continue through the weekend,
with a slight strengthening expected on Saturday. AIRMET TANGO
for low level turbulence will remain posted over and immediately
south through west of the mountains, with mention of tempo
moderate to isolated severe turbulence. AIRMET TANGO for strong
surface winds continues for Lanai and portions of the Big Island
as well. The prevailing trade winds are expected to veer a little
more east through Saturday.

Clouds and showers will continue to pass over the islands, focusing
along the windward and mountain areas and bringing brief MVFR
ceiling and VIS conditions. The stronger winds will help push
some showers to leeward areas of the smaller islands. Diurnal
cooling may lead to an increase in showers overnight, and AIRMET
SIERRA for mountain obscuration may become necessary if the
clouds and showers coverage become more widespread.

&&

.MARINE...
A rather busy period marine-wise.

The current north swell continues to fade this evening, although
it remains rather large over on the Big Island. A High Surf
Advisory is in effect for the north facing shores of the smaller
islands, while a High Surf Warning is still in place for the
northern shores of the Big Island. Both the High Surf Warning
and Advisory are good to until 10 am HST Saturday.

But as this swell continues to fade into Saturday, we will see
the warning level surf lowered to advisory, and the advisory level
surf possibly be canceled. We will be monitoring the near shore
buoys closely overnight.

A new north swell is due in on Sunday. It will smaller in
magnitude, but will likely bring on a high surf advisory for the
north facing shores of most islands. This means, the high surf
advisory for the Big Island, should it be extended, will be
expanded to cover the other islands affected by this new swell.

Besides the the advisory and warning for the north facing shores,
strong and gusty trades have produced an elevated trade wind
swell resulting in warning level surf for the eastern shores of
the Big Island and advisory level surf for the remaining islands
exposed to this swell. Slightly strong trades are on tap for
Sunday as a new surface high settles in north of the islands that
has the potential of bringing on gale force winds into some of
the channels as early as Saturday night. A Gale Watch is currently
in effect for the Pailolo and Alenuihaha channels, and Maalaea
Bay. The trades are not expected to ease off until Tuesday. With
this said, at least advisory level surf will continue through
early next week for the east facing shores.

Due to the combination of elevated swell and strong and gusty
trades, a Small Craft Advisory (SCA) is in effect for all
hawaiian waters, and it is likely to remain in effect through
early next week. Be advised, some of the marine zones may reach
gale force winds on Saturday night. A Gale Watch is currently in
effect for those selected waters.

A Marine Weather Statement is also in effect for the elevated
north swell which may result in large waves breaking in
harbor entrances and possible surges in harbors exposed to this
north swell.

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

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 10 AM HST Saturday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Olomana-
Molokai-Maui Windward West-Maui Leeward West-Maui Central Valley-
Windward Haleakala.

Wind Advisory until 6 PM HST Sunday for Lanai-Big Island North
and East-Kohala.

High Surf Warning until 10 AM HST Saturday for Big Island North
and East.

Small Craft Advisory until 6 PM HST Sunday 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-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

Gale Watch from Saturday evening through Sunday afternoon for
Maalaea Bay-Pailolo Channel-Alenuihaha Channel.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel.

&&

$$

DISCUSSION...Powell
AVIATION...Hui
MARINE...Lau



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