Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 271345
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
345 AM HST Mon Mar 27 2017

.SYNOPSIS...
A surface ridge will remain north of the islands through next
weekend. A ridge aloft will remain over the islands through the
middle of the week. During the second half of the week, a trough
aloft and a front will approach from the northwest. The front will
stall north of the area over the weekend. A strong new high will
build northeast of the islands early next week.

&&

.DISCUSSION...
A 1030 MB high lies about 1650 miles northeast of Honolulu near 36N
136W, with a surface ridge extending southwest from the high to 375
miles north of Honolulu. The ridge will remain north of the islands
through next weekend. The ridge will weaken over the next 12 hours
as a front passes by far north of the area. As a result, the trade
winds will weaken a bit and remain at moderate strength through
Friday.

A ridge aloft will remain over the main Hawaiian islands through
tomorrow night. The ridge will keep the atmosphere dry and stable,
so rainfall will remain light. Starting Wednesday, a deep trough
aloft and an associated front will approach from the northwest. The
front is expected to stall about 300 miles northwest of Kauai Friday
night, but atmosphere over the islands will become more moist and
less stable. Showers will likely become more active starting
Wednesday.

A strong new high will move east behind the front and is forecast to
be north of the islands by Friday night. Trade winds will strengthen
over the weekend and become quite breezy by early next week.

&&

.MARINE...
The current large west-northwest (WNW; 290-310 deg) swell will
slowly ease into Tuesday, then hold through mid week due to a slight
reinforcement Wednesday. A combination of this swell and fresh to
strong trade winds over waters around the Big Island will continue
to generate rough boating conditions today. The Small Craft Advisory
will remain up over most marine areas due to a combination of seas
and winds. Winds and seas are forecast to drop below advisory levels
through mid week (Tuesday through Thursday) as the ridge of high
pressure north of the state slightly weakens in response to a
passing cold front well north of the area. Another cold front is
forecast to approach the region later in the week, then stall and
weaken north and northwest of the area into the upcoming weekend.

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

Surf along south facing shores will likely remain up today due to
the large WNW swell wrapping around the islands and a small south-
southwest (SSW; 220 deg) long-period swell that is forecast to fill
in. A slight increase in surf along south facing shores is possible
Thursday through Saturday due to a long-period swell (190 deg)
associated with a low southeast of New Zealand.

Later in the week, the main forecast challenge will become centered
on another, potentially larger, WNW (310 deg) swell that will impact
the islands Thursday night through the weekend. A powerful low that
has already developed off the coast of Japan, based on the latest
satellite trends and surface analysis. An ASCAT pass overnight
reflected this developing system and showed a decent sized batch of
storm to near hurricane force winds (50-63 kt) out of the west
focused toward the region. Model consensus depicts this system
rapidly deepening to around 980 mb today while lifting northeastward
across the northwest Pacific. The westerly wind field associated
with this system is expected to expand through this period and
remain at storm force levels over a large area with seas reaching as
high 35 to 40 ft. As this system evolves and lifts northeastward to
the Date Line by mid week, a large westerly swell will result, that
could reach the islands as early as Thursday night, peak through the
day Friday, then slowly ease over the upcoming weekend. Some
uncertainty regarding the details this far out still exists due to
some model differences depicted between the ECMWF-Wave and GFS-
WAVEWATCH III solutions.
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.

&&

.AVIATION...
No AIRMETs are in effect and none are expected over the next couple
of days. Clouds and showers will remain sparse, so VFR ceilings and
visibilities will prevail. Moderate easterly trade winds will
continue.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 600 PM today for north and west facing
shores of Niihau, Kauai, Oahu and Molokai, north facing shores of
Maui, and west facing shores of the Big Island.

Small Craft Advisory through 600 PM Monday for all Hawaiian waters
except Oahu leeward waters and Maalaea Bay.

&&

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



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