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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 191955

Area Forecast Discussion
National Weather Service Honolulu HI
955 AM 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 morning. Visible satellite shows mostly
cloudy skies along windward slopes with mostly sunny to partly
cloudy skies leeward. Radar shows scattered showers drifting in
with the trade wind flow impacting windward slopes.

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.


Breezy east trade winds continue today. AIRMET TANGO for low level
turbulence is posted over and immediately south through west of
the islands. Expect this continue into tomorrow.

Clouds and showers will favor the windward and mountain areas.
Overall conditions should stay predominantly VFR with only brief
MVFR in passing showers. Morning soundings show the inversion
sloping from near 7 kft at PHLI to near 14 kft in PHTO. Most
cloud tops will remain below 10 kft over the smaller island. The
Big Island could see some tops reaching above 15 kft this
afternoon. However, most conditions should not warrant the need
for AIRMET SIERRA for mountain obscuration.


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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