Current Conditions
Temp-6.2 C
RH23 %
WindW 44 mph
RoadClosed
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Hawaiian Islands Synoptic Discussion and Guidance

254
FXHW60 PHFO 141354
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
354 AM HST Thu Dec 14 2017

.SYNOPSIS...
Cool and dry conditions will continue today, along with gusty
winds. Expect winds to taper off some tonight, while the cool
dewpoints will linger a bit into Friday. An upper level trough
approaching from the northeast tonight will bring unsettled
weather to portions of the state Friday and on through the
weekend. The most unstable airmass will be over the eastern
islands, and the waters to the northeast.

&&

.DISCUSSION...
No significant changes to the forecast in the short term, and only
some clean up in the longer term. A surface trough continued to be
analyzed to the southeast of the islands, and is expected to move
to the northwest towards the islands over the next 24 hours.
Meanwhile, and upper level trough is to the northeast of the
islands, and is expected to dig to the south and deepen. The
models generally agree on the trough cutting off into an upper
level low on Friday.

The High Wind Warning remains posted for the Big Island Summits.
Expect winds to increase over the next few hours, before started
to decline. However its possible the winds will remain within
advisory levels tonight. Wind at the lower elevations have been on
the increase, and are expected to increase a bit today, so a Wind
Advisory has been issued for the remaining areas, except for
Haleakala Summit. Anticipate the winds should fall below advisory
levels tonight.

The overnight sounding from Lihue was short, but got high enough
to sample the 500 mb temperatures at -10 celsius, which is on the
cold side of normal. Meanwhile the Hilo sounding reported a 500 mb
temperature of -13.9, which is colder than normal. The models
indicate the 500 mb temperature will warm a bit near Hilo over the
next 24 hours, to around -10. Meanwhile, colder upper level
temperatures will move in from the east associated with the upper
level trough. At the same time, an increase in low level moisture
is expected. This unstable airmass will bring an increase in
shower activity to the islands, but at this time not expecting it
to cause any significant issues. The airmass will be unstable
enough that a thunderstorm or two can not be ruled out. The
greatest chance will be over the windward waters tonight through
Saturday, and over portions of Maui and the Big Island Friday
afternoon.

The next weather pattern of concern is another upper level
disturbance that will approach the islands form the NW early next
week. The GFS and ECMWF agree with the general weather pattern,
but many of the finer details still need to be fleshed out with
future model runs. The GFS brings more moisture into the islands
that the ECMWF, and the GFS develops a stronger low closer to the
islands.

&&

.AVIATION...
Northerly flow will bring strong gusty winds to the Hawaiian
Islands over the next 24 hours. These winds will be strong enough
to produce moderate low level mechanical turbulence over and down
wind of mountain ranges. AIRMET Tango for tempo moderate low
level turbulence remains in effect for all islands.

Expect VFR conditions with isolated to scattered showers embedded
in the northerly flow.

&&

.MARINE...
A High Surf Warning remains in effect for north and west facing
shores of most islands with a High Surf Advisory (HSA) for north
facing shores of the Big Island through this evening. The current
northwest swell has peaked, but will still be quite large today,
before slowly subsiding through Saturday. Strengthening winds will
cause rough surf on east facing shores tonight into the weekend.
This surf may get big enough to require a HSA for east facing
shores.

A Small Craft Advisory (SCA) is in effect for most waters, with a
Gale Warning in effect for the Alenuihaha Channel. Seas are above
the 10 foot SCA threshold over areas exposed to the northwest
swell with winds above the 25 kt SCA threshold in most areas.
Northeast winds will peak today as the pressure gradient between
a high to the north and a trough to the east tightens. Winds will
subside tomorrow into Saturday as the trough approaches from the
east.

The approaching trough will bring increasing moisture and
instability, so thunderstorms are possible as early as this
evening over the windward waters of Maui and the Big Island, with
the chance lingering through Saturday.

See the Collaborative Surf Discussion for details on surf and
swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-Kona-
South Big Island-Big Island North and East-Kohala-Big Island
Interior.

High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Surf Advisory until 6 PM HST this evening for Big Island
North and East.

High Wind Warning until 6 PM HST this evening for Big Island
Summits.

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

Gale Warning until 6 PM HST this evening for Alenuihaha Channel.


&&

$$


DISCUSSION...M Ballard
AVIATION...Bohlin
MARINE...Donaldson

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