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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 170139

Area Forecast Discussion
National Weather Service Honolulu HI
339 PM HST Mon Jul 16 2018

High pressure north of the state will keep a moderate to breezy
trade wind flow in place through the upcoming weekend. Clouds and
showers will favor windward and mauka areas, with a few showers
spilling leeward from time to time.


Currently at the surface, a broad west-east oriented ridge of high
pressure is centered around 1125 miles north of Kauai. This is
maintaining moderate to locally breezy trade winds across the
island chain this afternoon. Visible satellite imagery shows
partly cloudy conditions across most of the state, with some
afternoon cloud build ups resulting in more extensive cloud cover
in a few areas. Radar imagery shows very little shower activity at
the moment, with showers primarily confined to interior sections
of Kauai. Main short term concern revolves around rain chances.

Model guidance is in good agreement showing a ridge of high
pressure holding in place to the north of the islands through
early next week, with a couple of disturbances passing by near or
to the south of the state during the period. The first
disturbance is expected to be a weak low or surface trough,
currently Invest 91C, passing by 300-400 miles south of the Big
Island on Wednesday. Another disturbance may pass over or near the
islands late in the weekend into early next week, but guidance
differs on the strength and location of this feature. Overall,
expect a fairly typical trade wind pattern to prevail, with mainly
scattered windward showers and isolated showers reaching leeward
areas from time to time. There may be a bit of an uptick in shower
activity Tuesday night and Wednesday, particularly over the
eastern end of the state, in association with the initial
disturbance passing by south of the Big Island. Another uptick in
shower activity will then be possible late in the weekend into
early next week in association with the second disturbance.
Moderate to locally breezy trade winds are expected to prevail
through the forecast period.


Moderate trade winds will persist through tonight, with a small
increase in wind speeds Tuesday. Clouds and showers carried by
the trade winds will remain concentrated over windward and
mountain areas of the state producing brief periods of MVFR
conditions in those areas. A few light showers may be carried over
to leeward sections of some of the smaller islands, but VFR
conditions are expected to prevail there.

No AIRMETs are expected through tonight.


Broad high pressure far north of the area will continue to produce
locally breezy east trade winds over the state for the next
several days. A Small Craft Advisory (SCA) is posted for the
typically windier waters around the Big Island and Maui County
through Tuesday afternoon, with an expansion of SCA conditions
likely thereafter. A low pressure system, which is expected to
pass south of the islands, Wednesday and Thursday, could also help
bump the trades up a notch, especially for the more southern

The locally breezy trade winds will continue to produce rough and
choppy surf along east facing shores, with surf heights nearing
the advisory level as winds increase by midweek. The
aforementioned low pressure system could also produce a short-
lived elevated east swell, mainly for the southeast and south
waters near the Big Island as it passes.

A series of reinforcing south and southwest swells will keep
small to moderate surf along the south and west facing shores
through most of the work week, with surf heights climbing a little
each day. Long term guidance shows a larger, longer period south
swell for the upcoming weekend, with surf heights nearing the
advisory level (8 ft) for south facing shores.


Small Craft Advisory until 6 PM HST Tuesday 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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