Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Honolulu HI
330 PM HST Thursday Apr 24 2014

Synopsis...
breezy trade winds will gradually increase into Friday and
Saturday...weaken Sunday and Monday...then recover by the middle of
next week as high pressure to our north fluctuates in strength.
Clouds and showers will favor windward and Mauka areas through the
forecast period.

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Discussion...
a 1029 mb high centered near 35n152w...about 930 miles north
northeast of the main Hawaiian islands...has ridges extending
southeast through 31n130w and southwest through 28n180w...spanning
the central North Pacific. The pressure gradient between the high
with its ridges to our north and equatorial low pressure is
sufficiently steep to support moderate to locally strong trade winds
across local waters this afternoon. Because of this...and because of
anticipated stronger winds Friday through Saturday...a Small Craft
Advisory is in effect for all local waters through Saturday
afternoon. Satellite loop shows patchy broken low clouds embedded in
the trades upwind from the islands...with a typical patchwork of
broken to overcast showery low clouds across windward and Mauka
sections of the smaller islands. Radar data shows scattered showers
across these same areas this afternoon. We expect this pattern will
continue into the weekend.

Models show the current trade wind pattern will continue into the
weekend. However...upper troughing expected to move in from the
northwest may weaken the ridge to our north Sunday and
Monday...causing trade winds to decrease on those days. Wind grids
were altered to reflect these weaker trades as well as for a
convective cloud and shower pattern across the islands Monday
afternoon. A stronger reinforcing high will move in from the
northwest early next week...steepening the pressure gradient and
boosting trade winds again by the middle of next week.

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Aviation...
strong trades east-NE g25-30kt continue to focus fast moving rain showers/rain
and isolate MVFR conditions along windward sections. Elsewhere mainly
VFR will prevail. Broken-overcast cirrus will increase at or above fl300 after 25/10z and
persist through the remainder of the period.

Airmet Tango remains posted for low level Lee turb due the strong trades.
This will remain in effect until further notice. High level chop may
increase after 25/10z over the western forecast area but should remain below airmet
criteria.

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Marine...
a Small Craft Advisory is in effect for all waters in anticipation
of strengthening winds and building combined seas through Saturday
afternoon. Northeasterly winds will reach their minimum speeds late
Sunday or Monday as the ridge to our north weakens...and then
increase again by the middle of next week.

Persistent trade winds will build seas...producing rough surf near
the advisory level along east-facing shores by Friday. Increasing
seas also contribute to the need for the Small Craft Advisory. Seas
will diminish with the winds late Saturday and Sunday.

A northwest swell will produce below-advisory surf along exposed
shores of the smaller islands today. The swell will drop Friday and
Saturday...but a small reinforcing northwest swell may arrive late
Sunday into Tuesday.

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Hfo watches/warnings/advisories...
Small Craft Advisory until 6 PM HST Saturday for all Hawaiian
waters-

&&

$$

Public/marine...Powell
aviation...dejesus