High Surf in Hawaii, January 21 to 24, 2017

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
503 AM HST Sat Jan 21 2017

.SYNOPSIS...
A weak cold front will move across the state today then stall
near the Big Island tonight through early next week. Very strong
and potentially damaging northeast trade winds are expected along
and behind the front this weekend, with winds easing early next
week.

&&

.DISCUSSION...
A weak cold front near Kauai early this morning will move southeast
down the island chain and stall near the Big Island tonight. This
front will be followed by a strong high pressure system pushing in
behind from the northwest. The tight pressure gradient between the
front and the high will result in strong, gusty, and potentially
locally damaging northeast trade winds. A High Wind Warning has
been issued for the entire state (except for Big Island summits
and Haleakala summit) for today and tonight. There is the
possibility for a Wind Advisory or an extension of the High Wind
Warning for all or portions of the state into Sunday.

The GFS and ECMWF are both showing winds around and just below
the inversion increasing to 40 to 45 kt when winds peak this
evening. This scenario often creates periods of strong, gusty, and
locally damaging winds over and downwind of terrain when the
inversion is based near or just above the mountains. Regarding
rainfall along the front, expect modest showers to be focused
along northern and windward slopes, but many of these showers
will track over to leeward sides of the islands due to the strong
winds. On Sunday, most of the rainfall will be focused over the
windward side of the Big Island, with drier and more stable air
from the surface high moving onto the western portions of the
state.

Winds will decrease and veer out of the east to east-southeast on
Monday and Tuesday as the high to the north is pushed off to the
east. The GFS and ECMWF are hinting at some of the dissipated
frontal moisture drifting back up over windward portions of the
state during this period. This effect is most prominent in the
GFS, which shows a disruption in the trade winds on Tuesday.
Otherwise, trade winds and a typical pattern of windward showers
should prevail through much of the work week.

&&

.AVIATION...
The frontal cloud band has reached Kauai early this morning and will
continue it's advance down the rest of the island chain today. Still
expect more widespread MVFR ceiling with showers conditions to
affect mainly windward and mountain areas. Winds have also increased
across the smaller islands and will become quite strong
northeasterly as the day progresses.

AIRMET for low level turbulence will be posted for much of the
islands early this morning. AIRMET for mountain obscuration along
windward areas is still a possibility with the increasing low
clouds.

&&

.MARINE...
Northwest swell continues to slowly decline at the nearshore
buoys overnight, and should decline further this morning based on
data from buoy 51101. We have cancelled the High Surf Advisory
for north and west facing shores of the smaller islands. Lingering
swell will still produce advisory-level surf along the west facing
shores of the Big Island today, where there is a lower criteria of
8 feet, and we have extended the High Surf Advisory there through
6 PM.

Incoming short-period north swell combined with building wind
waves due to the very strong northeast winds expected later today
through Sunday will push surf above advisory levels on east facing
shores of all islands. The High Surf Advisory remains in effect
for those areas from this afternoon through Sunday afternoon. This
advisory will probably need to be extended into Monday by a later
shift.

For the coastal waters, a Small Craft Advisory for all waters
this morning will give way to a Gale Warning this afternoon and
tonight as northeast winds continue to increase. The Gale Warning
has been extended through Sunday afternoon for the typically windy
areas around Maui County and the Big Island. Advisory-level winds
will very likely continue across all other waters where gales are
not present on Sunday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from noon today to 6 AM HST Sunday for all
portions of the state except for Big Island summits and Haleakala
summit.

High Surf Advisory from noon today to 6 PM HST Sunday for all east
facing shores except for Kahoolawe.

High Surf Advisory until 6 PM HST this evening for west facing of
the Big Island.

Small Craft Advisory until noon HST today for all Hawaiian
waters.

Gale Warning from noon today to 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Gale Warning from noon today to 6 AM HST Sunday for all remaining
coastal waters.

&&

DISCUSSION...Foster
AVIATION...Hui
MARINE...Jacobson