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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 291403 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
403 AM HST WED JUN 29 2016

Trade winds are expected to become strong and gusty by the end of
the work week as high pressure strengthens north of the islands.
Breezy to windy conditions are then expected to persist through
the holiday weekend. An upper level disturbance is forecast to
develop west of the island chain Today, leading to an increase in
trade wind showers, some of which could be heavy, especially on
Kauai and Oahu. As the disturbance moves west of the island chain,
a very dry and stable air mass will move over the state beginning
late on Thursday and continuing through Saturday. A more typical
trade wind shower pattern is expected to return for Sunday through
early next week.


Currently at the surface, a 1029 mb high is centered around 1800
miles northeast of Honolulu, and is driving the moderate trades
across the Aloha state. Infrared satellite imagery shows partly
cloudy skies in place in most areas, with some enhanced cloud
cover over windward areas and some upper level cloud cover in
places as well. Meanwhile, radar imagery shows scattered showers
drifting into windward and mauka locales, with mainly dry
conditions in leeward areas. Main short term concern for Today
revolves around rain chances.

Today and Tonight...
High pressure will shift slowly eastward to a location around
1350 miles north-northeast of Honolulu by Thursday morning. This
will keep a moderate trade wind flow in place across the island
chain through the period. Clouds and showers will focus primarily
over windward and mauka areas, although an occasional shower may
impact leeward areas of the smaller islands during the overnight
and early morning hours as well. Additionally, an upper level
disturbance will slowly get better organized west of the islands
through Thursday morning, and this will increase instability
across the state during the afternoon/evening hours, particularly
over the western islands. As a result, some afternoon/evening
shower development is expected in leeward areas as well.

Thursday through Saturday...
High pressure will strengthen north of the state, increasing the
trade wind flow across the island chains. Breezy to locally windy
trades are expected across the state through the period, with the
potential for the winds to reach advisory levels over portions and
possibly the entire state on Friday and Saturday. At the same
time, a much drier airmass originating from the desert southwest
in the mainland, will build in from the east. Additionally, the
upper level disturbance will lose its influence on the state as it
shifts further west and away from the island chain. Thursday will
be a transition day as instability decreases with the exit of the
upper level disturbance and arrival of the much drier airmass.
Showers will focus mainly over windward and mauka locales, but
some shower activity is expected in leeward areas as well.
Thursday night through Friday, the combination of low inversion
heights and a dry low level airmass, will result in much below
normal shower activity across the state, with showers primarily
limited to windward and mauka areas.

Sunday through next Tuesday...
Strong high pressure will remain nearly stationary north of the
Aloha state, keeping a breezy to locally windy trade wind pattern
in place. Model solutions show the atmosphere moistening back up
and inversion heights rising back closer to where they typically
reside, so we should see a more normal trade wind weather pattern
return. Clouds and showers are expected to focus primarily over
windward and mauka locales, but due to the strong trades,
an occasional shower will make it into leeward areas as well.


AIRMET Tango remains in effect for low level turbulence leeward
of the higher terrain on all islands. This AIRMET will likely
continue through this evening.

Brief MVFR conditions may occur today over windward and mauka
sections of the state due to low clouds and showers being carried
by the low level trade wind flow. Otherwise, expect VFR conditions
to prevail across the islands through this afternoon.

An upper level disturbance, which is forecast to move closer to
the western end of the island chain, may begin to cause increasing
atmospheric instability later today and tonight. If so, it is
possible that MVFR conditions may become more widespread tonight
over some windward facing slopes and higher terrain, especially on
Kauai and Oahu. There might also be periods of mountain
obscuration developing on some of the islands tonight.


A small craft advisory (SCA) has been posted for Maalaea Bay, and
the Pailolo and Alenuihaha Channels. Trade winds will increase
over the next few days with more marine zones likely to be added
to the SCA. Gale warnings for the Alenuihaha Channel are possible
starting Thursday night.

Surf will remain below advisory levels along all shorelines the next
several days. As trade winds strengthen late in the week, surf
along E facing shores will increase, and a high surf advisory
will likely be necessary over the weekend.


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




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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