Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 191927
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
927 AM HST Thu Jan 19 2017

.SYNOPSIS...
High pressure far east-northeast of the state will keep light to
moderate trade winds today. Winds will become locally light and
variable tonight and Friday as a front approaches from the
northwest. This front will advance across the smaller islands over
the weekend, then stall near the Big Island early next week. Look
for increasing showers across the state with the front. Behind the
front, very strong trade winds are expected for the state this
weekend, before easing early next week.

&&

.DISCUSSION...
No changes to the forecast package this morning.

A trade wind flow today, will give way to some lighter winds
tonight and tomorrow. At this time we expect the winds to become
light enough tonight for some localized land breezes to form, and
then some afternoon sea breezes tomorrow afternoon. Expect passing
showers through tomorrow afternoon.

A cold front approaching from the northwest will bring the next
round of unsettled weather. The front is expected to advance down
the island chain this weekend, before stalling near the Big Island
early next week. The front will bring showers to the islands, but
the bigger impact will likely be increasing winds behind the
front. A strong high pressure system forming to the northwest
behind the front will create a tight pressure gradient over the
islands. Winds initially behind the front will be from a more
northerly direction, bringing strong winds to some areas that
don`t typically receive strong winds under a trade wind flow. The
winds will be strongest over higher terrain, through mountain
gaps, and downslope of mountains. Winds will likely be strong
enough to reach advisory levels, so stay tuned as additional
model runs will help to refine the situation.

Early next week, the front will stall near the Big Island and
winds will veer to the east. Winds will then become more southeast
and then light as another front is expected to approach the
islands from the northwest. The long range models show it will be
the tail end of the front that reaches the islands, so the bulk of
the moisture is expected to the north and northeast of the area
Tuesday. The islands are expected to see moderate northerly winds
briefly after this front exits east.

&&

.AVIATION...
A high pressure ridge north of the Hawaiian Islands will weaken
ahead of a cold front approaching from the northwest. Winds will
weaken today and bring overnight drainage winds to sheltered
airfields. AIRMET Tango remains in effect for low level turbulence
over and downwind of the terrain of all islands. Boundary layer
winds are expected to diminish later this morning and the AIRMET
will be cancelled when this occurs. Stronger winds will redevelop
this weekend as the front arrives.

Isolated MVFR ceilings may develop briefly over windward areas of
the Hawaiian Islands through tonight. Leeward areas will remain
VFR.

&&

.MARINE...
The current large west northwest swell appears to have peaked at
the Hanalei buoy but continues to rise at the nearshore buoys
around Oahu, Maui, and Lanai. We will leave the current warnings
and advisories in place today. This swell will lower gradually
later today and tonight with the current warnings likely being
downgraded to an advisory. However a new northwest swell is
expected to arrive later tonight and Friday with advisory level
surf expected. If the swell turns out to be bigger than
predicated, than low end warning level is a possibility. We will
wait to see the readings from the northwest buoys before making
this decision. Another large northwest swell is expected to arrive
Monday night and Tuesday. Current guidance indicates that this
swell will reach High Surf Warning levels.

Strengthening winds behind a cold front passing across the area
this weekend will cause for a significant increase in short period
choppy surf along north and east facing shorelines. There will
also be a series of small, mainly background south swells
throughout the forecast period.

A Small Craft Advisory remains posted for most Hawaiian coastal
waters due to the large west northwest swell moving across the
area. Strengthening winds behind the above mentioned front will
cause Small Craft Advisory conditions across the entire area and
possibly gale force conditions over the typically windy waters
around Maui County and The Big Island.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui
Windward West-Maui Central Valley-Windward Haleakala-Kona-Kohala.

High Surf Advisory until 6 PM HST this evening for Waianae Coast.

Small Craft Advisory until 6 PM HST this evening for all
Hawaiian waters except Maalaea Bay-

&&

$$

DISCUSSION...M Ballard
AVIATION...Bohlin
MARINE...Burke/Stall



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