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Temp-0.1 C
RH95 %
WindE 17 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

286
FXHW60 PHFO 190630
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Mon Sep 18 2017

.SYNOPSIS...
High pressure to the north of the islands will keep a moderate to
breezy trade wind flow in place through the remainder of the work
week. The trades will ease to light and locally moderate levels
over the weekend into early next week, as the high north of the
State weakens. Showers will favor windward and mauka areas through
the period, with a stray shower reaching leeward areas from time
to time. Showers will be most prevalent during the night and
morning hours.

&&

.DISCUSSION...
Currently at the surface, a 1031 mb high is centered around 1400
miles to the north-northeast of Honolulu, and is driving the breezy
trade winds across the island chain this evening. Infrared
satellite imagery shows partly cloudy skies in most areas, with a
few patches of enhanced cloud cover riding into windward areas
with the trades. Meanwhile, radar imagery shows scattered windward
showers with a stray shower drifting leeward from time to time.
Main short term concerns revolve around trends in the trade wind
speeds and rain chances.

Tonight through Friday,
High pressure to the north-northeast of the island chain will
maintain a moderate to breezy trade wind flow through the
remainder of the work week, but we should see a gradual decrease
in the trade winds speeds as the weak progresses. Bands of clouds
and showers will continue to drift through the island chain, with
the showers focusing primarily over windward and mauka areas
during the night and morning hours. A stray shower may also drift
into leeward areas from time to time due to the strength of the
trades.

Friday night through next Monday,
High pressure will weaken and shift eastward well to the northeast
of the State over the weekend into early next week, as a cold
front tracks eastward across the central Pacific well north of the
island chain. This will likely result in a decrease in the trade
wind speeds across the area, with generally light to locally
moderate trades expected. Additionally, some localized land and
sea breezes may become more prominent in the more sheltered areas.
A windward/mauka favored shower pattern is expected to continue
through the period, although we may see an increase in leeward and
interior shower development during the afternoon and evening due
to the easing of the trades and an upper level trough in the
vicinity of the islands.

&&

.AVIATION...
Strong high pressure fare N of the islands will support breezy
trade winds. AIRMET Tango will remain in effect through 24 hours
and beyond.

Ragged clouds and showers, carried in by trade winds, will favor
the windward slopes and coasts of all islands. Partly cloudy skies
are expected overnight across leeward areas. Inland showers are
expected to redevelop Tuesday Afternoon across leeward Big Island.
Brief MVFR conditions possible in showers statewide, otherwise
VFR conditions will prevail all areas.

&&

.MARINE...
Strong high pressure far NNE of the islands will support fresh to
strong trade winds as it remains nearly stationary through
Wednesday. The high will gradually diminish late in the week and
over the weekend, with the associated ridge being shunted toward
the islands as a front approaches from the NW. This will lead to
a gradual decrease in trade wind speeds, especially over the
weekend, potentially continuing into early next week. A Small
Craft Advisory (SCA) will gradually be pared back in area as
winds diminish, but will likely be necessary for the windiest
zones through at least Thursday.

The nearby and upstream fetch of elevated trade winds will support
choppy short-period surf along E facing shores as wind waves come
ashore. Otherwise, the only significant swell source is a low to
the NW that will send a 3-4' WNW swell toward the islands that
will likely arrive Thursday and peak on Friday. See the latest
Oahu Surf Discussion (SRDHFO) for additional details.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Tuesday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bedal
MARINE...Birchard

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