Drought in Hawaii, January 1 to 16, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
808 PM HST Sun Dec 31 2017

.SYNOPSIS...
A dry trade wind pattern is expected through the week as high
pressure prevails over the region. Trades may briefly weaken over
the smaller northwest islands New Years Day through Tuesday as a
front passes to the north.

&&

.DISCUSSION...
Dry and stable conditions are expected to hold across the region
through the first week of the new year as deep layer ridging
prevails. Satellite imagery this evening showed bands of
stratocumulus clouds with tops capped under a strong subsidence
inversion around or under 6 kft approaching and moving through the
islands from the east within the trades. Although periods with
mostly cloudy skies are resulting over windward areas from this
coverage, little to no rainfall is occurring. The latest state
rainfall summary reflected this over the past 12 to 24 hrs and only
shows a hundredth of an inch from a few stations (max of five
hundredths at Saddle Quarry on the Big Island). The trend is
expected to persist through the week. The best chance for any
showers will remain over windward locations due to these bands of
clouds moving through, mainly through the overnight and early
morning periods each day.

Trades are forecast to slightly trend down later tonight through
Tuesday, mainly over and around Kauai and Oahu, as a weakness
within the ridge develops in response to a passing front well to
the north. Guidance remains in good agreement Wednesday through
the second half of the week and supports breezy trades returning
as high pressure builds north of the state.

Looking ahead into next weekend, ensemble guidance depicts a
similar dry trade wind pattern persisting with deep layer ridging
holding in place and cold fronts passing to the north.

&&

.AVIATION...
High pressure north of the state will keep light to moderate
trade winds in place through New Years Day. A very dry airmass
will greatly limit shower activity, with only very light showers
periodically affecting windward and mauka areas. Elsewhere, rain
free conditions are expected. Brief MVFR cigs may affect windward
areas, but predominantly VFR conditions are expected at all
terminals through the TAF forecast period. No AIRMETs are in
effect and none are anticipated through New Years Day.

&&

.MARINE...
A Small Craft Advisory (SCA) remains in effect through Monday
afternoon for the typically windy waters adjacent to the islands
of Maui County and the Big Island. The trades are forecast to
weaken below the SCA criteria from Monday night into Tuesday as a
weak front passes by north of the state.

A small northwest swell will continue through New Years Day, with
surf remaining well below the High Surf Advisory thresholds along
north and west facing shores. A larger northwest swell arriving
early Tuesday, is expected to peak late Tuesday, producing surf
near the High Surf Advisory criteria along most north and west
facing shores of the smaller islands. Combined seas are forecast
to reach the SCA criteria of 10 feet over waters exposed to the
large northwest swell. This SCA may be required from Tuesday into
Wednesday over waters adjacent to Kauai, as well as the Oahu and
Maui County Windward Waters. In addition, SCA winds will likely
return to the typically windy waters starting late Tuesday, and
continuing through the end of the work week, as surface high
pressure builds far north and northeast of the region.

The northwest swell is expected to gradually subside from late
Wednesday through early Friday. The Wave Watch III model shows a
long-period west-northwest swell arriving Friday. This swell
appears to gradually build through Saturday, with surf heights
potentially approaching the High Surf Advisory threshold along
some north and west facing shores of the smaller islands from
late Saturday into Sunday.

Short-period trade wind swell will continue to generate moderate
rough surf along east facing shores through most of this week.
Surf along south facing shores is expected remain very small,
which is indicative of typical winter time conditions, through
the upcoming week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

AVIATION...Jelsema
MARINE...Houston
REST OF DISCUSSION...Gibbs