Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 261347
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
345 AM HST Sun Mar 26 2017

.SYNOPSIS...
A surface high to the north will move east through tomorrow, then
become nearly stationary far northeast of the islands. A ridge aloft
will remain over the islands through the middle of next week. By the
end of the week, a trough aloft and a front will approach from the
northwest.

&&

.DISCUSSION...
A 1028 MB high about 1000 miles northeast of Honolulu near 32N 148W
is forecast to move east today, then become nearly stationary
tomorrow about 1500 miles northeast of Honolulu near 35N 135W. A
surface ridge extending west from the high will remain north of the
islands through the week. The high will keep breezy trade winds
blowing over the islands today. A ridge aloft will remain over the
main Hawaiian islands through the first half of the week, keeping
the weather quite dry.

A trough aloft will move eastward to the north of the islands
tomorrow. The surface high moving away to the east and the trough
aloft passing by will combine to weaken the trade winds tonight
through tomorrow. The trade winds will strengthen again on Tuesday,
but the trades won`t get as breezy as they will be today. The
atmosphere will remain dry and stable through the middle of the
week, so rainfall will remain light.

Toward the end of the week, a deep trough aloft and an associated
front will approach from the northwest. The surface ridge will shift
south closer to the islands and the atmosphere will become more
moist and less stable. Showers will likely become more active late
in the week.

&&

.AVIATION...
Locally strong NE to E winds and a strong and low temperature
inversion will produce conditions favorable for low level
turbulence. AIRMET TANGO will remain up through at least today for
OCNL MOD TURB southwest through west of the mountains of all
islands. Clouds and showers will remain sparse, so VFR ceilings and
visibilities will prevail.

&&

.MARINE...
Hazardous boating and beach conditions will continue into Monday
before trending down into mid week due to a combination of fresh to
strong trade winds and a large west-northwest (WNW; 300-310 deg)
swell that is currently building down the island chain this morning.
These conditions have led to a Small Craft Advisory for all Hawaiian
waters due to winds (25 to 30 kts, strongest in the channels) and/or
seas (10 ft or greater) through Monday. The large WNW swell will
generate life-threatening surf along exposed north and west facing
shores into Monday before slowly trending down into mid week.

For the building WNW swell, the latest PacIOOS nearshore buoy
observations are remaining in good agreement with the latest wave
model guidance. However, a few observations at the Waimea buoy
spiked into the 9 to 12 ft range a couple of times through the
overnight hours. Although these random spikes in wave heights appear
to have been or could have been spurious (a few feet higher than the
fully exposed Hanalei buoy), the north facing shores of Oahu have
been added in the warning this morning. The west side of Oahu was
left in the advisory, due to the anticipated shadowing associated
with this westerly swell direction. Elsewhere, wave heights are up
to around 9 ft at Hanalei and around 7 ft at the Pauwela buoy. The
offshore buoys northwest of Kauai appear to have peaked with heights
ranging from 11 to 13 ft, which is the predicted peak of this swell
event.

Surf along east facing shores will remain small and choppy through
the upcoming week due to moderate to strong onshore winds
persisting.

Surf along south facing shores could see a slight increase late
today due to the previously discussed WNW swell wrapping around the
islands. A slight increase in surf along south facing shores will
also become a possibility Thursday through Saturday due to a long-
period swell (190 deg) associated with recent activity across the
southern Pacific.

For the outlook, another large long-period WNW (310 deg) swell will
be possible across the islands Thursday night through the weekend.
The latest deterministic and ensemble guidance remain in decent
agreement over the next few days and depict a storm-force low
developing off the coast of Japan Sunday night into Monday, then
tracking ENE to the Date Line Tuesday night into Wednesday while
intensifying (to around 970 mb low). A large batch of gale-to-storm
force westerly winds focused toward the region through this time is
forecast with seas peaking within the 30 to 40 ft range. Swell
across the islands associated with this storm will likely lead to
another period of warning-level surf and advisory-level seas. More
details will follow in later packages this week as this system
evolves and confidence increases with regard to specifics on arrival
times and impacts.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 600 AM Monday for north and west facing
shores of Niihau and Kauai, north facing shores of Oahu and west
facing shores of the Big Island.

High Surf Advisory until 600 AM Monday for north and west facing
shores of Molokai, west facing shores of Oahu and north facing
shores of Maui.

Small Craft Advisory through 600 pM Monday for all Hawaiian Waters.

&&

$$
MARINE...Gibbs
REMAINDER...Donaldson


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