746 
FXHW60 PHFO 132011
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1011 AM HST Fri Dec 13 2019

.SYNOPSIS...
Breezy to locally windy trade winds are expected today as strong 
high pressure passes well to our north. The trades will bring
rainfall to mostly windward and mauka locales, with a few showers
briefly reaching leeward. The high level jet stream will bring 
increasing high clouds later today into tonight. Trade winds will
decrease during the weekend as the high moves away. A dry, stable
airmass will take control of our weather this weekend and the 
first half of next week, with few showers and considerable 
sunshine. A new high passing far to the north will return locally 
windy trades Monday and Tuesday.

&&

.DISCUSSION...
The stationary front that was just NW of Kauai is beginning to
retreat westward away from the islands as a surface trough. This 
is allowing breezy to locally windy trades to return as a surface
high passes about 900 miles N of the islands today. An upper 
trough just W of the islands has been helping to reinforce the 
front, and enhance incoming trade wind showers. The upper trough 
is expected to weaken as we head into the weekend, which will 
result in fewer and less intense showers. High level moisture 
riding in on the subtropical jet will continue to bring high 
clouds at times, and these will increase tonight into Saturday 
before pushing away later Saturday as the jet shifts to the SE of 
the islands.

The surface high to the N will continue eastward into the weekend,
so trade wind speeds on Saturday will be a notch below today's
levels. Winds will even be a notch lower on Sunday as a col 
between two highs passes N of the islands. The next surface high 
will pass well N of the islands on Monday, returning breezy to 
locally windy trade wind speeds for Mon and Tue. The winds should 
ease Wed, but may increase again on Thu as the next in the series 
of highs passing to the N approaches our longitude.

Trade wind showers are expected to continue to decrease as we head
into the weekend, with decreasing precipitable water and warming
mid-level temperatures. A strong 700 mb high just to our N will
bring warm mid-level air early next week. This, combined with a 
lack of moisture, should yield a significant minimum in trade wind
showers Tue and Wed, with nice fine weather expected. Showers may
increase again Thu as the mid-level high moves away and the
airmass becomes a bit more unstable again.

&&

.AVIATION...
An area of enhanced moisture continues to reside over the islands
this morning in a association with a dissipating front. Greatest 
coverage of showers will remain over mainly interior/windward
areas of Oahu and Kauai as well as windward areas of the 
remaining islands. Brief MVFR conditions and mountain obscuration
may occur due to the passing showers. 

Surface high pressure to the northeast of the state will allow 
for moderate to occasionally breezy easterly trades to persist 
through the period.

No AIRMETs are currently in effect. 

&&

.MARINE...
The current northwest swell will continue to subside from west to
east over the next few days. The High Surf Advisory remains posted
for north and west facing shores of Kauai County, Oahu, and
Molokai and north facing shores of Maui. Surf is expected to fall
below advisory levels by early tomorrow morning. A short period 
north-northeast swell will increase surf along exposed east facing
shores, mainly on Kauai and Oahu, today and tonight, but should 
stay just below the advisory levels. 

A reinforcing large northwest swell is forecast to build late
Sunday into Monday and peak Monday night, possibly near warning
levels. This swell should slowly decline Tuesday into Wednesday, 
but will likely be reinforced by another large northwest swell 
Wednesday night into Thursday. 

A high pressure north of the state will keep moderate to locally 
strong trade winds over the area through Saturday. The combination
of the current northwest swell and the strong trade winds is 
resulting in a Small Craft Advisory for all coastal waters, except
the Maui leeward waters. This Small Craft configuration is 
expected to be trimmed down to mainly the locally windier waters 
around the Big Island and Maui County by tomorrow morning as the 
swell subsides. 

A slight decline in trade winds and period without Small Craft 
conditions is possible Sunday as the current high moves east and 
a new high builds north. Trade winds should return to moderate to
locally strong speeds by early next week and seas will build with
the reinforcing northwest swell. 

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Saturday for N and W facing
shores of Niihau, Kauai, Oahu, Molokai, and N facing shores of
Maui.

Small Craft Advisory until 6 AM HST Saturday for all Hawaiian 
Coastal Waters except for Maui County Leeward Waters.

&&

$$

DISCUSSION...R Ballard
AVIATION...Thomas
MARINE...EATON