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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 020636
Area Forecast Discussion
National Weather Service Honolulu HI
836 PM HST FRI JUL 1 2016
Strong and gusty trade winds will affect the state through
Saturday, with a slight drop in winds expected for the rest of
the holiday weekend. A dry and stable air mass will result in
rather dry conditions with very little rainfall through Saturday.
The airmass will gradually moisten from the east through the
remainder of the holiday weekend, leading to increased showers
that will periodically spread leeward on the smaller islands.
Dry and windy conditions prevail across the Aloha State on this
Friday evening. Rain gauge and radar data show very little recent
shower activity even over the windward areas. The strong trade
winds are being driven by surface high pressure centered about
1200 miles NNE of Oahu. Aloft, an upper level low is centered
several hundred miles west of Kauai, and continues to bring high-
level cloudiness over the islands. A mid level ridge is located
just to the northeast of the islands, and a very stable airmass is
present over the state. The 00Z soundings show low inversions
based between 4500 and 5000 feet, with PW values ranging from 1.2
to 1.3 inches.
A few locations around the state have observed wind advisory
criteria conditions of 30 mph sustained wind or 50 mph wind gusts
during the day, mainly on the Big Island but also on Lanai and
Oahu, as well as the Haleakala summit. Most areas have seen
sustained winds of 20-25 mph and peak gusts in the 40-45 mph
range. The latest model guidance continues to indicate that the
strongest winds will occur overnight into Saturday, when a weak
lower/mid level trough approaching the islands from the southeast
will tighten the gradient further. Model soundings show low-
level winds increasing to around 30 kt during this time, with the
inversion remaining strong and lower than usual. This combination
of factors will continue to produce conditions conducive for
strong wind gusts over and downwind of island terrain. A wind
advisory remains in place through Saturday afternoon for the
entire state, and there is a small chance that the Haleakala
summit will see high wind warning conditions overnight. Otherwise,
expect mainly dry conditions to prevail overnight, with areas of
low clouds over windward areas and areas of high clouds statewide.
The existing forecast appears to be on track, and no updates are
planned for this evening.
Rather dry conditions will hold into Saturday. The above mentioned
mid level ridge and unusually low inversion will keep low-level
moisture minimal. Windward terrain may squeeze out some light
showers, but dry conditions will dominate.
Trade winds will back off slightly by Sunday, and shower activity
is expected to return to more normal levels. The above-mentioned,
broad, mid level trough will pass over the islands from east to
west. While the surface high to the north will change little, the
easing of the mid level pressure gradient and rising of the
inversion is expected to cause winds to decrease enough to drop
the wind advisory. The mid level trough will also bring an
increase in low level moisture that will boost shower activity
back to normal levels. Expect mainly windward rainfall, with
breezy trade winds carrying a few showers over leeward portions of
the smaller islands at times.
The high clouds that have been producing periods of interesting
sky conditions during the past several days will thin over at
least the eastern half of the state on Saturday as the upper
level low to our west drifts further away and ridging noses in
from the southeast. Thicker high clouds will likely return by
Tuesday and continue through midweek as the upper trough to our
west strengthens once again.
Strong, gusty trade winds and stable atmospheric conditions will
persist across the island chain through Saturday. Numerous PIREPS
support the continuation of AIRMET Tango, for moderate to
isolated severe low level turbulence over and immediately S
through W of terrain on all islands. Sustained surface wind
speeds of 30 knots or greater is also included in AIRMET Tango.
VFR conditions will prevail, with the stable trade wind flow
providing shallow low clouds that may occasionally become
widespread enough along windward slopes and coasts to lead to
isolated MVFR ceilings.
Elevated trade winds will hold through the holiday weekend. A late
morning ASCAT pass detected winds of at least 30 kt in the
Alenuihaha Channel and near South Point, and with a further
increase in winds expected tonight into Saturday, a gale warning
remains in effect for these areas as well as the Pailolo Channel.
A Small Craft Advisory (SCA) remains posted for the rest of the
coastal waters and channels through Sunday, and the SCA will
likely remain in place for most waters through the holiday
Rough, advisory-level surf will be possible along the east facing
shores over the weekend, beginning as early as late Saturday.
Although east shore surf is expected to peak around the 8 foot
advisory level, rather high afternoon tides could produce run up
issues, such as along Kamehameha Hwy on windward Oahu. Elsewhere, no
significant surf is anticipated through the middle of next week.
A 2 to 3 foot south swell is due next Thursday and Friday. Please
refer to the recently issued Collaborative Nearshore Swell and
Wind Forecast (SRDHFO) for more details.
Strong and gusty trade winds and a rather dry air mass will
remain over the islands through Saturday. Rainfall received in
late May slightly eased drought conditions across the islands,
which rules out the possibility of Red Flag Warning criteria
being met. However, fire danger will be elevated due to the
strong winds and low afternoon humidities.
Wind Advisory until 6 PM HST Saturday for all Hawaii islands.
Gale Warning until 6 PM HST Saturday for Pailolo Channel-
Alenuihaha Channel-Big Island Leeward Waters-Big Island
Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Maalaea Bay-
Big Island Windward Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office