Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 270645
Area Forecast Discussion
National Weather Service Honolulu HI
845 PM HST Sun Mar 26 2017
A surface high to the northeast will move east through tomorrow
night, then become nearly stationary far northeast of the islands. A
ridge aloft will remain over the islands through the middle of the
week. By the end of the week, a trough aloft and a front will
approach from the northwest. The front will stall north of the area
next weekend. A strong new high will build northeast of the islands
early next week.
A 1030 MB high lies about 1300 miles northeast of Honolulu near 34N
143W, with a surface ridge extending southwest from the high to 425
miles north of Honolulu. The ridge will keep breezy trade winds
blowing over the islands tonight. Weather will remain mostly dry
overnight, but the trades are pushing a few showers over windward
areas of Maui and Molokai.
A surface ridge will remain north of the islands through the week
and maintain trade winds over the islands. The ridge will weaken
over the next 24 hours as a front passes by far north of the area.
As a result, the trade winds will weaken. The trade winds will
strengthen again on Tuesday, but the trades won`t get as breezy as
they were over the weekend.
A ridge aloft will remain over the main Hawaiian islands through the
first half of the week. The ridge will keep the atmosphere
dry and stable, 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
starting Wednesday night.
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.
The current large west-northwest (WNW; 290-310 deg) swell will hold
through Monday. A High Surf Advisory will remain up for exposed
shores through Monday with surf dropping below advisory levels
Monday night into mid week. A combination of the WNW swell and fresh
to strong trade winds over the channels and waters around the Big
Island will continue to generate rough boating conditions through
Monday. The Small Craft Advisory will also remain up over the
exposed northwest waters into Monday, due to seas holding around 10
ft. Winds and seas are forecast to remain 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 cold
front passing well north of the area. Another cold front is forecast
to approach the region later in the week, then stall and weaken
north of the area over the 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 into Monday due
to the current 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 SE of New Zealand.
Later in the week, the main forecast challenge or focus will become
centered on another, potentially larger, WNW (310 deg) swell that
will fill in and impact the islands Thursday night through the
weekend. This swell will be associated with a powerful low that has
already begun to develop off the coast of Japan today, based on the
latest satellite trends and surface analysis. An ASCAT pass earlier
today also reflected this developing system and showed a decent
sized batch of gales (35-40 kt) out of the west focused toward the
region. Model consensus depicts this system rapidly deepening from
1000 mb this evening to around 980 mb by Monday evening while
lifting northeastward across the northwest Pacific. The westerly
wind field associated with this system is expected to expand through
this period and reach gale to 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.
Locally strong NE to E winds and a strong and low temperature
inversion will continue to produce conditions favorable for low
level turbulence this evening. AIRMET TANGO remains up for OCNL MOD
TURB southwest of the mountains of all island. Winds are expected to
weaken overnight, and AIRMET TANGO will likely be cancelled by
Monday morning. Clouds and showers will remain sparse, so VFR
ceilings and visibilities will prevail.
High Surf Advisory until 600 PM Monday 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 AM Monday for Oahu leeward waters
and Maalaea Bay.
Small Craft Advisory through 600 PM Monday for the rest of the