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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 270640

Area Forecast Discussion
National Weather Service Honolulu HI
840 PM HST THU MAY 26 2016

A convective pattern will prevail through the weekend, especially
for the smaller islands, as a trough northwest of the islands
keeps winds light and from the southeast. Land and sea breezes
will form, causing clouds and showers to favor mauka and leeward
areas each afternoon and evening. Nights and early mornings will
be clearer and drier. A shower band will move south over the
islands through the middle of next week and trade winds are
expected to briefly return behind the band.


A 1032 MB surface high far northeast of the main Hawaiian Islands
would normally drive at least moderate trade flow across local
waters. However, a surface trough northwest of Kauai continues to
push into the southwestern flank of the high, slackening the
pressure gradient across the islands and causing winds to veer to
southeasterlies. Afternoon soundings show PW near 1.4 inches with
negative lifted index values, moist and unstable enough to support
brief bouts of enhanced showers. Satellite loop shows an upper
trough persists north of the area. Models show this feature will
be with us into early next week, acting to keep the atmosphere
unusually moist and unstable. The surface trough northwest of
Kauai will shift south slowly through the weekend. This will keep
prevailing low level flow over the islands light and generally
out of the southeast. The southeast flow will be partly blocked by
the Big Island, so winds will be light and variable over the
smaller islands. Afternoon sea breezes will produce clouds and
showers over interior and leeward areas of all the islands with
partial clearing at night.

Models show a new surface high will move east along 30N. Trade
winds driven by this high will push a shower band southeast
across the islands during the middle of next week, with moderate
trade winds expected to arrive behind the front. However, models
are not in good agreement on when this shower band will reach the
islands so timing confidence is low. We expect that trade winds
returning next week behind the front will not last long and may
fade out again by the end of next week.


A weak wind regime will remain in place tonight and Friday across
the smaller islands, with overnight land breezes and daytime sea
breezes expected. Predominantly VFR conditions are expected at the
terminals overnight, although brief MVFR cigs/vsbys will be
possible in passing SHRA, primarily at the windward TAF sites.
Showers are expected to develop over the mountains and interior of
the islands again on Friday.

Airmet Sierra is in effect for mountain obscuration across Oahu.
Conditions are expected to improve here later this evening.


Winds and combined seas will remain below small craft advisory
criteria through the forecast period.

A moderate southwest swell from the Tasman sea is expected to
peak Friday, then decline during the weekend. Since there are so
many islands along the path of the swell, surf is likely to be
inconsistent. A small northwest swell arriving Sunday will peak
Monday well below the advisory threshold. See the the
Collaborative Near-shore Swell and Wind Forecast (SRDHFO) for
details on this swell. Otherwise rather small surf is expected.






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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