Current Conditions
Temp2.5 C
RH87 %
WindNNE 14 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 191330

Area Forecast Discussion
National Weather Service Honolulu HI
330 AM HST Tue Sep 19 2017

High pressure to the north-northeast 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.


Currently at the surface, a 1030 mb high centered around 1350
miles to the north-northeast of Honolulu, is driving moderate
trade winds across the island chain early this morning. Infrared
satellite imagery shows clear to 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.

Today 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

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 afternoons and evenings due to
the easing of the trades and an upper level trough in the
vicinity of the islands.


The Strong High far north of the islands will continue to support
breezy trade winds. AIRMET Tango remains in effect.

Ragged clouds and isolated showers carried in by the trade winds
will favor the eastern exposures of all islands both day and
night. Convective showers are expected to redevelop over interior
and leeward portions of the Big Island this afternoon and persist
through early evening. Brief MVFR conditions possible in showers
statewide, otherwise VFR conditions will prevail all areas.


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 is posted for marine zones where winds are most
accelerated by island terrain, and has been extended into

The nearby and upstream fetch of elevated trade winds will support
choppy short-period surf along E facing shores the next couple of
days. Otherwise, the only significant swell source is a low to
the NW that will send a 3' WNW swell toward the islands Thursday
and Friday. The recently updated Oahu Surf Discussion (SRDHFO)
has additional information on swell sources.


Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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