Current Conditions
Temp-2.3 C
RH68 %
WindN 28 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

277
FXHW60 PHFO 011400
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST FRI JUL 1 2016

.SYNOPSIS...
Strong trade winds will affect the state today through Saturday,
with breezy conditions persisting through the rest of the holiday
weekend. A dry and stable air mass moving over the islands will
result in mainly dry conditions with very little rainfall through
Saturday. The airmass will gradually moisten from Saturday night
through Monday, leading to increased trade wind showers that will
spread leeward on the smaller islands. Less wind and fewer showers
are expected by the middle of next week.

&&

.DISCUSSION...
Dry conditions prevail across the state on this early Friday
morning, with very little shower activity detected by area
radars. Trade winds have decoupled over some lower elevation
areas during the past few hours, but remain rather strong at
higher elevations. These winds are being driven by a 1032 mb high
centered about 1200 miles northeast of Oahu. Aloft, a mid/upper
level low is retreating westward near 25N170W, while a mid level
ridge builds over the state from the east. Mimic-TPW satellite
imagery and model data show a notably dry airmass spreading into
the islands from the east. The 12Z Hilo sounding clearly shows the
major airmass change which has taken place over eastern parts of
the state during the night, with a very strong and unusually low
inversion based around 2500 feet. The 12Z Lihue sounding showed a
more typical pattern just to the west of the advancing dry/stable
airmass, with the inversion based near 5500 feet.

The surface high initially centered far northeast of the islands
will strengthen somewhat and move slowly west during the next
couple of days. While winds are initially lower at some locations
early this morning, both observed data and model guidance indicate
that winds will increase sharply during the day. Forecast
soundings indicate that the low-level subsidence inversion will
strengthen and drop to very low levels statewide today, down near
2000 feet according to the GFS. Considering the observed 12Z Hilo
sounding, this process appears to be already taking place. The
interaction between strengthening low-level winds, the strong
stability and island terrain is expected to cause locally strong
wind gusts, especially over mountain ridges and to the lee of the
mountains. A wind advisory remains in effect from this morning
through Saturday afternoon. Latest guidance continue to indicate
that the peak of the low-level winds will probably occur tonight
into Saturday. Otherwise, expect dry conditions to prevail today
and tonight, with only a slight chance for light showers even
across windward areas.

The base of the inversion will gradually rise from late Saturday
into Monday, as moisture embedded within the trade wind flow
increases toward more typical levels. The GFS and ECWMF have been
consistent with most aspects of the forecast through the weekend,
so confidence remains fairly high. This moistening is expected to
lead to gradually increasing trade wind showers, with breezy trade
winds delivering passing showers for holiday outdoor activities on
Sunday and Monday. With the moisture depth increasing to near 10
kft by Sunday night or Monday, showers may more easily spread
leeward on the smaller islands, with the potential for the trade
wind flow to become somewhat showery into Wednesday. Diminishing
moisture is expected to lead to fewer trade showers for the second
half of next week, while trade wind speeds gradually ease.

&&

.FIRE WEATHER...
Strong/gusty trade winds and a rather dry air mass will settle
over the islands today 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
during this event. However, fire danger will be somewhat elevated
due to the strong winds and fairly low afternoon humidities.

&&

.AVIATION...
Strong and gusty trade winds and stable atmospheric conditions
will persist across the island chain through Saturday. Therefore,
AIRMET Tango remains in effect for low level turbulence over and
immediately leeward of the higher terrain on all islands. In
addition, we will also include sustained surface wind speeds of 30
knots or greater, as well as the potential for isolated severe
turbulence across the leeward areas, when we update AIRMET Tango
starting at daybreak this morning.

Even though drier conditions will continue to spread from east to
west across the island chain this morning, a few low clouds and
brief showers may impact some windward facing slopes and
mountains. This may result in localized MVFR ceilings or
visibilities. Otherwise, expect VFR conditions to prevail across
most areas, especially from late this morning through early this
evening.

&&

.MARINE...
Strong trade winds associated with high pressure building south and
southwest toward the state will generate rough conditions across the
waters through the weekend. Gale force winds are expected over the
typical windier locations through Saturday, which lines up well
withe latest model guidance. Trade winds will slightly ease Sunday
through Tuesday. The latest nearshore wave model guidance indicates
the maximum seas reaching the 12 to 14 ft range across the
Alenuihaha Channel and over the nearshore waters south of the Big
Island through this time.

Advisory-level surf will be possible along the east facing beaches
over the weekend, beginning as early as Friday night into Saturday.
This will be in response to the persistent strong trade winds
expected. Elsewhere, no significant surf is anticipated at this time
through the weekend. Looking ahead through the upcoming week, the
latest WW3 and ECMWF-Wave and ensemble wave guidance depict a good
sized batch of gales setting up just east of New Zealand today into
the weekend within Hawaii's swell window. This setup will likely
translate to moderate surf along south facing beaches by the end of
next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 6 AM this morning to 6 PM HST Saturday for
Niihau-Kauai-Oahu-Molokai-Lanai-Kahoolawe-Maui-Kona-South Big
Island-Big Island North and East-Kohala-Big Island Interior.

Gale Warning until 6 PM HST Saturday for Pailolo Channel-
Alenuihaha Channel-Big Island Leeward Waters- Big Island Southeast
Waters.

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.

&&

$$

DISCUSSION/FIRE WEATHER...Jacobson
AVIATION...Houston
MARINE...Gibbs

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office