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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 301357 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
357 AM HST Thu Mar 30 2017
Light trade winds over the western end of the state will allow
for leeward afternoon sea breezes over Kauai and Oahu today, which
will leave to 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.
No changes to the forecast with the morning package. High pressure
to the northeast of the state continues to bring trade winds to
the eastern end of the state.
The overnight sounding at Lihue had a precipitable water (PW)
value of 1.03 while Hilo had 1.26 inches, which matches well with
the satellite derive PW. A check upstream shows little change in
the PW value, so not expecting any significant change in shower
Over the western end of the state, the winds are a bit lighter,
which will continue to allow some afternoon sea breezes to set up
over leeward areas, similar to what occurred yesterday. This will
bring some clouds and a few showers to those areas during the
High pressure is expected to build north of the state Friday,
strengthening the trade winds, which will bring a return to a
more typical trade wind weather pattern. Trades are expected to
increase this weekend to breezy to windy levels, with showers
mainly impacting windward and mauka areas.
Heading into the middle of next week, trade winds will weaken as
the high pressure weakens and a cold front passes by to the north
of the islands.
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. Localized MVFR CIGS/VIS
can be expected for those areas, mainly overnight and early
morning. No AIRMETs are expected at this time.
A large west-northwest swell (290-310 deg) associated with a
strong weather system far northwest of the state should reach the
islands tonight, peak Friday and Friday night, then slowly ease
over the weekend. Warning- and/or advisory-level surf for exposed
north- and west-facing beaches is expected during this time. All
of the models remain in close agreement for seas to ramp up
quickly tonight 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 due to
moderate to fresh onshore winds. Surf will begin to build over the
weekend as trade 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 next week.
A slight increase in surf along south-facing shores is possible
today through Saturday due to a long-period swell (190 deg) from
recent activity across the southern Pacific. In addition to this
south 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.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office