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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 240637

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Thu Mar 23 2017

A trade wind weather regime will continue at least through the
upcoming weekend. Showers riding in with the winds will favor the
windward and mountain areas, especially during the night and morning
hours. The strength of the trades will increase to moderate to
locally strong briefly for the next couple of days.


A line of low clouds continues to affect windward Maui and Big
Island, and to a lesser extend, windward Molokai this evening,
bringing some persistent showers to those areas. Radar data
indicated windward east Maui and well as west Maui are seeing the
most of these showers. Gages in those areas are not picking up much
rainfall though, with only one site on West Maui reporting nearly a
quarter of an inch in the past three hours. Satellite imagery
revealed this line of low clouds extending some distances east of
the islands. Therefore, expect the clouds and showers to continue to
affect those areas through rest of the evening into early Friday
morning. Some of these low clouds will eventually reach windward
Oahu and even Kauai, though it will probably be early Friday. Rather
fair weather continues for rest of the state and will stay that way
through early Friday. There are still some high clouds over the Big
Island and these will exit east of the state overnight.

A surface high pressure currently north-northeast of the islands
will move to far northeast of the area Friday, then back build a bit
westward over the rest of the weekend before settling off the west
coast early next week. In the mean time, trade winds will prevail
across the area. This high is expected to strengthen a bit over the
weekend, resulting in trade winds increasing a notch across the
state, becoming locally strong over the weekend. The aforementioned
line of low clouds will still be in the island vicinity early part
of Friday, providing clouds and showers mainly to the windward and
mountain areas. Forecast solutions hinted drier airmass may reach
the islands by the later part of Friday. Thus, an improvement in the
weather is expected for the windward areas by then.

Trade wind weather is here to stay through next week, as indicated
by forecast models. Typical low clouds embedded in the trade wind
flow will reach the islands at times, bringing some showers to
mainly windward and mountain areas. Airmass is expected to remain
somewhat stable and so rainfall amounts will not be a cause for

The trades may weaken a bit toward the later part of next week, as
forecast solutions indicate a stronger front may approach the area
from the west.


Low clouds from an old frontal boundary are embedded within
prevailing easterly flow. These clouds will produce isolated to
scattered showers with brief periods of MVFR ceilings along
eastern slopes of all islands during the overnight period. Drier
VFR conditions expected elsewhere.

No AIRMETS are in effect.


A new high is expected to become established to the northeast of
the islands tomorrow, which will help to strengthen winds
beginning Friday. Winds could reach Small Craft Advisory (SCA) levels
by Friday afternoon in the typical windier locations. Winds are
then expected to strengthen further this weekend with moderate to
locally breezy conditions expected, due to a new high developing
to the north of the islands.

A very large west-northwest swell is expected to build across the
island chain Saturday and Saturday night, with at least high end
advisory level surf for north and west facing shores. Surf will
be the largest on Kauai and Niihau, and slightly lower over the
rest of the islands due to some island shadowing. Rough and
choppy conditions will persist along east facing shores due to the
strengthening trade winds this weekend. The incoming swell will
also raise seas to SCA levels this weekend.






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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