Scientific Forecaster Discussion
fxhw60 phfo 300155
Area forecast discussion
National Weather Service Honolulu HI
355 PM HST Wed Mar 29 2017
light trade winds over the western end of the state will allow
for leeward afternoon sea breezes over Kauai and Oahu Thursday with
increasing afternoon clouds and brief showers. Moderate trade
winds will continue over the rest of the state with passing
windward showers. Trade winds will become breezy over the weekend
with increasing windward rainfall expected.
high pressure located in the east Pacific is maintaining moderate
trade winds over the eastern half of the state with light east
southeast flow over the Western Islands. An area of clouds and
showers currently east of The Big Island will bring increasing
windward showers to the Hilo and puna districts tonight.
The lighter winds over the Western Islands will allow for
afternoon leeward sea breezes over Kauai and Oahu Thursday, with
increasing afternoon clouds and showers over the interior island
areas. Passing windward showers will continue over Maui County and
The Big Island. This pattern will continue through Thursday before
high pressure gradually builds north of the state Friday. Trade
winds will increase in response, with breezy to windy conditions
expected over the weekend and into next week. Showers will also
increase with a focus over windward and mountain areas, with
spotty showers over leeward locations. Weaker trade wind flow is
expected by midweek as high pressure weakens and a cold front
passes by to the north.
moderate trade winds will continue for the next few days. No
significant weather features are expected. Clouds and showers will
favor the windward and mountain areas. Periods of MVFR ceilings/visible
can be expected for those areas, mainly overnight and early
morning. No airmets are expected at this time.
An upper level trough and jet is helping to produce light to
moderate turbulence between fl300/360 more than 250 nm northeast
of the state. The trough and jet are shifting to the east,
therefore no airmet Tango will be issued.
surf along north and west facing shores is somewhat higher than
expected today due to a reinforcing northwest swell and looks to
remain so through Thursday, though still below advisory level.
The latest surface analysis showed a 998 mb storm-force low
centered around 1600 nm northwest of Kauai just west of the date
line with a large area of west-northwest storm-force winds
(focused within the 290 to 310 directional band relative to the
islands) just to its south and west. According to the latest
altimeter passes, seas associated with this system continue to
range from 30 to 35 ft over The Heart of the fetch region focused
toward the islands, which has been persistent for the past several
passes. This low is forecast to track east-northeast across the
North Pacific through the week.
A large west-northwest swell (290-310 deg) associated with this
system should reach the islands Thursday night, peak Friday and
Friday night, then slowly ease over the weekend. Warning-level
surf for exposed north and west facing beaches and advisory-level
seas are expected during this time. All of the models remain in
close agreement for seas to ramp up quickly Thursday night to Small
Craft Advisory levels and peak in the 10 to 14 ft range Friday,
before slowly easing through the weekend. If the swell comes in
larger or later than predicted, warning-level surf could continue
into Saturday before dropping to advisory levels Sunday.
Local winds and seas will likely remain below advisory levels
through Friday as the ridge of high pressure north of the state
slightly weakens in response to a cold front that is forecast to
approach the region later in the week. Advisory-level trade winds
will return across portions of the waters over the weekend as high
pressure builds north of the state behind this front.
Surf along east facing shores will remain small and choppy through
the week due to moderate to fresh onshore winds. Surf will begin
to build over the weekend as easterly winds strengthen locally
and upstream of the islands, and may near or reach advisory levels
along east facing shores by the end of the weekend and into early
A slight increase in surf along south facing shores is possible
Thursday through Saturday due to a long-period swell (190 deg)
from recent activity across the southern Pacific. In addition to
this southerly swell, wrap from the previously discussed large
west-northwest swell will add some to the mix by Friday at select
spots along exposed southern facing beaches.