Current Conditions
Temp-1.2 C
RH55 %
WindSSW 25 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 010630

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST THU JUN 30 2016

Trade winds will continue over the islands for the foreseeable
future, becoming quite strong Friday and Saturday, and remaining
that way through 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.


Dry conditions prevail across the state on this Thursday evening,
with very little shower activity detected by area radars. Breezy
trade 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 00Z Hilo sounding displayed initial indications
of this dry and stable airmass, with the inversion down to around
5000 feet. The 00Z Lihue sounding showed a more typical pattern
with the inversion near 6000 feet.

Little rainfall is expected across the state overnight, as the
very dry and stable airmass continues to spread westward over the
islands. The existing forecast shows only slight rain chances even
for windward areas, which appears to be on track. No updates are
planned for this evening.

The surface high initially centered far northeast of the islands
will strengthen somewhat and move slowly west during the next
couple of days. This will lead to increasing trade winds, with
breezy to windy conditions expected from Friday through the
holiday weekend. Forecast soundings indicate that the low-level
subsidence inversion will strengthen and drop to very low levels
on Friday, down below 2000 feet according to the GFS, before
gradually rising on Saturday through Sunday. Windward shower
chances through Saturday will be quite low, and any precipitation
that occurs will be very light.

The interaction between the strengthening 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 has been posted in anticipation of
this for Friday morning through Saturday afternoon. Latest
guidance continue to indicate that the peak of the low-level
winds will probably occur Friday night into Saturday.

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, 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.

A persistent and slow-moving trough aloft will remain several
hundred miles west of the islands through the middle of next
week. This feature is expected to remain sufficiently far from the
islands to not destabilize the island atmosphere, but associated
southwest flow over the islands will carry varying amounts of
mid- and high-level clouds over the islands into the middle of
next week.


Breezy and gusty trade winds and a rather dry air mass will settle
over the islands Friday through Saturday. Rainfall received in
late May slightly eased drought conditions across the islands,
which rules out the possibility of a Red Flag warning being
issued. However, fire danger will be somewhat elevated.


Trade wind speeds will strengthen as atmospheric stability
increases from tonight into Friday. Therefore, AIRMET Tango will
likely remain in effect through Friday for low level turbulence
over and immediately leeward of the higher terrain on all islands.
Note that it may be necessary to also include sustained surface
wind speeds of 30 knots or greater, as well as isolated severe
turbulence across the leeward areas in AIRMET Tango starting
around daybreak on Friday.

While conditions will be trending drier during the next 12 hours
or so, a few low clouds and brief showers may impact some
windward facing slopes and mountains through early Friday
morning. This may result in brief MVFR ceilings or visibilities.
Otherwise, expect VFR conditions to prevail across most areas,
especially on Friday.


A small craft advisory (SCA) is posted for all Hawaiian waters,
and a gale warning will go into effect Friday morning for marine
zones around Maui and the Big Island, where winds are most
accelerated by island terrain. These headlines will remain in
place through at least Saturday, with SCA winds/seas prevailing
through the bulk of the holiday weekend.

Surf is expected to remain below the high surf advisory criteria
along all shorelines through Friday. The strong trade winds will
drive an increase in short-period wind waves to the point that high
surf is expected along E facing shores over the weekend and early
next week. A high surf advisory is likely to be issued some time on


Wind Advisory from 6 AM Friday 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.

Small Craft Advisory until 6 AM HST Friday for Pailolo Channel-
Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Gale Warning from 6 AM Friday to 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.




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