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RH9 %
WindENE 31 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

022
FXHW60 PHFO 182007
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1007 AM HST Wed Jan 18 2017

.SYNOPSIS...
High pressure east northeast of the state will keep mainly
moderate to fresh trade winds through Thursday. Winds will become
light and variable Thursday night and Friday as a front approaches
from the northwest. A front will push down the island chain
Friday night through Saturday night, then stalling out near the
Big Island through early next week. The front will bring increasing
showers to windward and mauka areas with some of the showers
reaching leeward areas as well. Additionally, very strong trade
winds are expected to overspread the state this weekend, before
easing early next week.

&&

.DISCUSSION...
A 1025 mb high is centered about 1000 miles east northeast of
Hawaii, with an east-west oriented ridge passing 225 miles north
of Kauai. The high is driving mainly moderate to fresh trade
winds across the state this morning, with some stronger winds in
exposed areas. Visible satellite shows stable, stratocumulus clouds
over windward waters tracking in from the east and impacting some
of the windward sides of the islands. Little, if any rain is
falling from these clouds. As the inversion is low and strong
which is capping the incoming clouds, leeward areas and waters are
mostly sunny this morning. Speaking of the inversion, 12Z
soundings at Lihue and Hilo show inversion heights about 4500 to
5000 feet.

A cold front is located nearly 1200 miles northwest of Kauai moving
eastward at 20 mph. As the front approaches the state, the high
will weaken causing our trade winds to weaken. This will occur
gradually on Thursday and Friday, with nighttime land breezes and
daytime sea breezes taking beginning around Thursday night. A dry
and stable airmass is expected to remain in place ahead of the
front, so expect little in the way of precipitation over the next
couple of days. Winds aloft on the southern end of high are a bit
stronger and bringing advisory strength winds on the Big Island
summits. A Wind Advisory goes through today, and should trend down
as the high pressure system to the east northeast weakens.

Northeast winds will dramatically increase Friday night into
Saturday as the cold front reaches the state and a strong high
follows. The strong pressure gradient between these two features
will result in very windy trade winds through the weekend. Winds
will likely be strong enough for a Wind Advisory for all or
portions of the state, though it is too early to issue this
product. We have highlighted this event with a Special Weather
Statement (SPSHFO) available on our website. Along with the
winds, an increase in rain is expected. Showers will be most
prevalent across windward and mauka areas, but with the increasing
trades and rising inversion heights, some of the showers will
reach leeward areas of the smaller islands as well. There remains
some uncertainty regarding the southward push of the front, with
indications in the latest model solutions that it may hang up near
or over the Big Island Sunday into early next week. As a result,
will show a drying trend across the smaller islands Sunday into
early next week, while keeping windward sections of the Big Island
and Maui a bit more unsettled.


&&

.AVIATION...
Locally breezy trade winds will continue to transport low
clouds and isolated showers mainly along windward facing slopes
and shorelines of the islands today. Localized MVFR CIGS possible
over windward sections due to these passing low clouds and
showers. Otherwise, VFR conditions are expected to prevail.

AIRMET Tango remains in effect for TEMPO moderate low-level
turbulence leeward of the mountains on all islands due to the
breezy low-level trade wind flow. This AIRMET will likely
continue into tonight, but may not be necessary on Thursday,
since the trade wind speeds are expected to decrease within the
next 24 hours.

AIRMET Sierra for MTN obscuration over Kauai has been canceled.
Ceilings have lifted due to daytime heating. Conditions may
redevelop later this evening.


&&

.MARINE...
Data from buoys 51001 and 51101 northwest of the state are
showing the new west northwest swell is gradually filling in but
is slower in arriving based on wave model guidance. Surf along
north and west facing shores will gradually build today, peak
overnight, then lower gradually lower Thursday and Thursday night.
With the more westerly direction of this swell, high surf will
also reach west facing shores of The Big Island by tonight.
Another large northwest swell is expected to arrive Thursday night
and Friday with advisory level surf expected. This swell will
lower gradually over the weekend. A short period north northeast
swell is expected over the weekend behind a cold front moving
across the area. The swell will gradually swing around to the east
early next week. Advisory level surf is likely along north and
east facing shores with this new swell.

A Small Craft Advisory is presently posted for most Hawaiian
coastal waters mainly due to seas associated with the new west
northwest swell arriving. Winds around portions of The Big Island
are also reaching Small Craft Advisory levels. Winds are expected
to drop off later today and tonight. Winds behind a cold front
moving across the chain this weekend will cause winds to exceed
advisory criteria and could reach Gale Warning levels across some
areas.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning from noon today to 6 AM HST Thursday for
Niihau-Kauai Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-
Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Surf Advisory from noon today to 6 AM HST Thursday for
Waianae Coast.

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

Small Craft Advisory until 6 AM HST Thursday for all Hawaiian
waters except Maalaea Bay-

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay.


&&

$$

DISCUSSION...Foster
AVIATION...Bedal
MARINE...Burke/Stall

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