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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 200202

Area Forecast Discussion
National Weather Service Honolulu HI
402 PM HST Tue Sep 19 2017

High pressure to the north northeast of the islands will keep a
moderate trade wind flow in place through the remainder of the
work week. The trades will weaken to gentle breezes this weekend
into early next week, as the high 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.


A 1030 mb surface high centered around 1350 miles north northeast
of the area is driving mainly moderate trade winds across the
Hawaiian Islands this afternoon. Visible satellite shows partly
to mostly cloudy skies around the state with some leeward areas
seeing some afternoon cloud build ups on Maui and the Big Island
which are blocked from the trades. An upper level low is centered
about 1000 miles northeast of the state. The low is causing a
weaker and somewhat elevated inversion at Hilo this afternoon
according to the sounding. Radar shows a few showers associated
with the afternoon sea breeze along the Kona coast.

The high will remain nearly stationary and persistent in strength
through the end of the work week. Bands of clouds and showers
will continue to carry over the islands with the trades, with the
showers focusing primarily over windward and mauka areas. A few
showers may track over to leeward sides of the smaller islands at

The high will weaken and shift east this 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 gentle 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.


AIRMET TANGO for low level turbulence will remain posted over and
immediately south through west of the islands tonight and likely
into tomorrow. Expect similar conditions Wednesday with moderate
to locally breezy trade winds and clouds and showers favoring the
windward and mountain areas. Cloud and shower maxima will occur
overnight and in the early morning hours, introducing possible
periods of MVFR CIGS/VIS. Otherwise, predominately VFR conditions
will prevail.


A strong high pressure system remains far NNE of the main
Hawaiian Islands. This will be producing moderate to fresh trade
winds across most of the coastal waters with stronger winds in
the usually windier areas south of the Big Island and in the
channels around Maui County. A Small Craft Advisory will remain
in effect for these windier coastal waters until later in the week
when the high weakens and the ridge is pushed closer to the state
by an approaching front.

The enhanced trade wind fetch will continue to support choppy
short-period surf along the east-facing shores over the next
couple of days. For the north- and west-facing shores, a low
pressure system far to the northwest is producing a swell train
that will be about 3 ft when it reaches the state late Wednesday
and into Thursday.


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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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