High Surf in Hawaii, February 6 to 9, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
349 AM HST Thu Feb 6 2020

.SYNOPSIS...
The leading edge of a cold front is passing through Maui County
this morning will continue to produce numerous showers along the
frontal band. Clouds and enhanced showers associated with this
frontal band will move eastward into the Big Island later this
morning. Expect showers, heavy at times, with a few thunderstorms
possible along the front. Cold northerly to northwesterly winds
will blow in behind the front followed dropping high and low
temperatures by 3 to 6 degrees below normal into early next week.
Modest showers will prevail over north facing slopes through the
weekend. Unsettled weather with additional periods of heavy
showers are possible early next week as another cutoff low
meanders just north of the island chain.

&&

.DISCUSSION...
The short term weather forecast continues to trend wet across the
state as a cold front sweeps from west to east down the island
chain. Radar and satellite imagery this evening shows the cold
front producing numerous showers from Kauai to Maui County with
rainfall rates over 1 inch per hour in some locations. Heavy
rainfall over Kauai this morning produced Flash Flooding along the
Hanalei River as reported by Kauai Emergency Management. These
moderate to heavy showers will continue to develop over Kauai
through mid morning before decreasing in intensity. Additional
moderate to heavy showers are moving into Oahu this morning just
in time for the morning commute. The cold front will move into the
Big Island around noon today, enhancing showers across the
island. Expect up to 5 inches of storm total snowfall on the Big
Island summits through Friday above the 10,500 foot elevation
level. A Winter Weather Advisory for snow remains in effect.

Cold northerly to northwesterly winds will blow in behind the
front lasting through the weekend with passing showers favoring
northern slopes of each island through the weekend. These cold
northerly winds will cause temperatures to fall 3 to 6 degrees
below normal for this time of year across the region. Meanwhile,
an extended period of strong winds will also develop over the Big
Island summits of Mauna Kea and Mauna Loa today as wind speeds
will increase above advisory levels by Thursday morning, then
increase above High Wind Warning thresholds by Thursday afternoon.
The High Wind Watch was upgraded to a High Wind Warning this
morning for both summits on the Big Island with the morning
forecast grid package.

An upper level low will deepen just north of the Hawaiian Islands
lasting through the weekend. This cold core upper low will keep
unsettled weather in the forecast through Sunday with enhanced
clouds and passing showers favoring northern slopes of each
island.

Another unstable upper low moves into the state from the north on
Sunday night. Long range model guidance keeps this low in a
meandering orbit just north of the Hawaiian Islands through much
of the week. Upper level troughs wrapping around this low will
bring periods of numerous showers to each island next week.
Temperatures are forecast to remain slightly below normal through
the first half of next week. The upper level low will likely
remain close enough to the islands for strong upper level winds
extending the strong and gusty winds over the Big Island summits
where High Wind Advisory and Warning thresholds may be exceeded
with additional snowfall possible on the highest peaks.Stay tuned
for forecast updates to both the wind and precipitation elements
for next week as the timing of these impacts for each island will
likely be adjusted.

&&

.AVIATION...
A cold front, currently over Maui County, will continue
southeastward to the Big Island later today through tonight.
Clouds and showers accompanying this front will lead to sub VFR
CIGS/VSBYS periodically. In addition to showers along and ahead
of the front, gusty northerly winds combined with a sufficient
amount of moisture will support showery conditions continuing for
northern and windward slopes today. Drier air will gradually begin
to fill in from west to east by tonight as high pressure builds to
the north.

AIRMET SIERRA remains in effect for tempo mountain obscurations
in clouds and showers from Kauai to Maui. Expect this to be
expanded to the Big Island later today. Additionally, some light
icing in the layered clouds is also expected along the front.

&&

.MARINE...
A front near Oahu will move southeast, pushing past coastal
waters Friday and moving southeast of the offshore waters by
Saturday. Gentle to locally fresh southeast winds ahead of the
front have been shifting rapidly to locally strong north winds
behind the front. A Small Craft Advisory (SCA) is in effect for
the coastal waters around Kauai starting this evening due to the
strong north winds. The SCA will likely be expanded and extended
due to large seas from a series of swells.

A surface low is forecast to develop about 800 nm northeast of
Oahu Thursday night, then strengthen to gale force and move
southwest. North winds will strengthen to near-gale force over
the northwest offshore waters with gales possible. Strong to near-
gale force winds are expected over the coastal waters. Winds are
expected to peak on Friday, then gradually subside.

A series of large swells will impact the islands through the
weekend. A northwest swell building this evening will peak
Thursday. A High Surf Advisory remains in effect for north and
west facing shores of the smaller islands for surf from this
swell. The gale developing north of the area will produce a north
northwest swell reinforcing the high surf along north facing
shores. A very large northwest swell arriving early next week may
produce surf reaching warning levels along north and west facing
shores by Monday night.

A short-period swell will maintain moderate surf along east
facing shores through Friday. The large north swell Friday and
Saturday will also refract some energy into exposed east facing
shores, possibly requiring a High Surf Advisory there as well.
A small rise in surf is possible along south facing shores through
the coming weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Olomana-
Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Wind Warning from 6 AM this morning to 11 AM HST Sunday for
Big Island Summits.

Winter Weather Advisory from noon today to 6 AM HST Friday for
Big Island Summits.

Small Craft Advisory until 6 PM HST Friday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel.

Small Craft Advisory from 6 AM this morning to 6 PM HST Friday
for Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters.

&&

DISCUSSION...Bohlin
AVIATION...Gibbs
MARINE...Powell