Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Honolulu HI
404 am HST Tue Dec 6 2016

Synopsis...
a surface trough east of The Big Island is moving to the west. A
new upper level trough will move towards the islands during the
second half of the week. A weak ridge north of the area through
Thursday will keep light trade winds that will allow afternoon sea
breezes, along with clouds and showers, and overnight land breezes
in many locations. The new upper level trough could bring
additional showers to the islands.

&&

Discussion...
some minor tweaks to the forecast package have been made, but the
general forecast philosophy remains the same.

The mid level trough near Kauai earlier has lifted to the north,
but a surface trough east of The Big Island is moving towards the
islands. A weak ridge north of the islands is helping to maintain a
weak trade wind flow. That being said, the winds are expected to
be light enough over the next couple of days for some local land
and sea breezes to set up. This will mean clouds and showers
increasing during the afternoon hours, primarily over Oahu and the
islands of Maui County.

The overnight sounding from Hilo had 1.83 inches of precipitable
water which is wetter than normal, while Lihue had 1.19 which is
near normal for December. Showers are limited over The Big Island,
but plenty of clouds, particularly high clouds, continue to move
overhead. Satellite derived precipitable waters shows the higher
swath of moisture east of The Big Island likely associated with
the surface trough mentioned above.

The GFS and European model (ecmwf) both show an upper level trough near the
dateline moving to the east through the week, with the trough
approaching the islands towards the end of the week. This trough
will bring cooler temperatures aloft, but the timing of the cooler
temperatures won't necessarily coincide with the increased
moisture. Overall the GFS has colder temperatures at 500 and 700
mb than the European model (ecmwf). At this time the forecast reflects an increase
in showers at the end of the week and into the weekend. Will have
to watch future runs to see if the instability parameters become
better aligned.

Winds over The Big Island summits came down overnight, so the Wind
Advisory has been canceled. The European model (ecmwf) suggests winds might
increase near advisory levels again tonight, while the GFS keeps
the winds below. The current forecast keeps winds in line with the
GFS solution.

&&

Aviation...
VFR conditions will prevail across the state today. Isolated MVFR
conditions will be possible with widely scattered showers through
the morning. MVFR conditions may become more likely over the
islands this afternoon when showers and clouds are forecast to
increase somewhat.

No airmets are in effect at this time.

&&

Marine...
a weak surface trough over the waters will continue to impact the
local area through midweek. A weak ridge of high pressure will build
west over the area later in the week as a the surface trough lifts
north and away from the waters. This pattern will result in a weak
pressure gradient over the state and a continuation of light winds
each day over much of the region.

The latest surface analysis showed a gale centered around 1100 nm
northeast of Oahu and a 1037 mb high centered over the date line to
its west-northwest. As this gale lifts northeastward and away from
the region through the mid-week period, the pressure gradient will
remain strong between these two synoptic features. The latest
ensemble and deterministic wave model guidance remains in good
agreement through this time and depicts the seas ranging from 10 to
15 ft due to strong northerly flow in this region well north-
northeast of the state. As a result, the 10 to 11 second northerly
energy will persist across the local waters through Thursday and
will gradually shift to the north-northeast as it fades later in the
week. Surf associated with this source will remain well below
advisory levels each day along the exposed beaches.

A new long-period west-northwest (310 deg) swell associated with a
recent storm over the northwest Pacific is forecast to fill in
Tuesday night, peak Wednesday, then slowly ease through the
remainder of the week. Outside of the European model (ecmwf)-wave being slightly
larger at the peak of this swell, the wave guidance remains in good
agreement. Surf heights will remain well below advisory levels from
this source along north and west facing shores.

A small lingering easterly swell that was generated last week due to
the strong trade winds over and upstream of the islands will
continue to steadily ease through the week. Surf along eastern
facing shores will respond and likely drop below three ft by
Thursday, then near flat levels through the upcoming weekend.

Surf along the Southern Shores managed to climb into the three to
five foot (face value) range through the day on Monday at select
spots due to a recent southern hemisphere source. This southerly
source will likely hold today before easing through the remainder of
the week. Guidance supports a smaller southwest swell filling in
Sunday night through Tuesday.

For the long range (late next week), despite the model differences
between the European model (ecmwf) and the GFS, the European model (ecmwf)-wave along with the
NCEP/fnmoc and gwes ensemble guidance all depict a potentially
sizable west-northwest swell approaching and filling in by the end
of next week. The European model (ecmwf) depicts a large batch of gales favorable for
the islands setting up over the northwest Pacific south-southeast of
the Kamchatka peninsula over the upcoming weekend and into early
next week. Later model runs will need be monitored for better
agreement through the rest of the week.

&&

Hfo watches/warnings/advisories...
none.

&&

$$

Discussion...M Ballard
aviation...Jacobson
marine...Gibbs

National Weather Service Glossary of Abbreviations