High Surf in Hawaii, March 1 to 3, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
847 PM HST Wed Feb 28 2018

.SYNOPSIS...
A strong high pressure ridge northeast of the Hawaiian Islands
and a deepening low pressure system to the west will produce
strong and gusty east-southeast winds through Thursday. An upper
level trough will rotate through the islands on Thursday
enhancing showers. The greatest chances for rain showers will
remain along the windward and mountain slopes through the week. A
drying trend with decreasing wind speeds remains in the forecast
for this weekend.

&&

.DISCUSSION...
An upper level trough rotating around a low pressure system 450
miles west of Kauai will enhance showers across the state
tonight and tomorrow. Water Vapor satellite and radar imagery
already shows enhanced convective showers moving towards Niihau
and Kauai from the southwest this evening with high cirrus clouds
streaming across the rest of the state. Expected rainfall rates
will be moderate with locally heavy showers possible, confidence
remains low for flooding concerns at this time. We will continue
to closely monitor the showers as they evolve overnight.

Otherwise a strong high pressure ridge northeast of the islands
and a surface low to the west continues to tighten local area
surface pressure gradients. Strong east-southeasterly winds are
creating interesting localized wind effects across the islands.
Some locations are observing strong advisory level wind speeds
with reports of tree damage, while in other areas the wind flow is
blocked by terrain and wind speeds are light. A wind advisory
remains in effect for most areas of the state until 6 PM HST
Thursday afternoon.

On Friday, surface wind speeds begin to decrease as the ridge
north of the state begins to weaken and the low to the west slowly
drifts northward. An upper level jet stream will continue to
produce high cirrus cloud cover and maintain scattered windward
and mountain showers through the upcoming weekend.

In the long range forecast a 1042 mb surface high far to the north
of the state will interact with a low pressure system off the
California coast allowing a shallow cold front to pass through the
islands early next week. Expect slightly cooler temperatures as we
return to northeasterly winds with more typical isolated to
scattered windward and mountain showers.

&&

.AVIATION...
The islands will remain under a stiff E to SE low level wind flow
through Thursday, although not as strong as in the past couple of
days. There are areas of calmness under this wind flow, due to
terrain blockage, thus making the wind forecast somewhat
challenging. Never-the-less, AIRMET Tango remains in effect for
mechanical turbulence over S through W of all mountain ranges
below 7k feet. This AIRMET will continue UFN, as a strong surface
high remains parked some 800 nm NNE of the islands.

The winds are picking up fragmented pieces of low clouds, and
carrying them over to all the islands. Primary recipients are the
windward and mountain areas of the islands. Some of these showers
have and will drift into the leeward areas of the smaller islands
overnight and into Thursday morning. Some of these showers are
rather prevalent, resulting in AIRMET Sierra for mountain
obscuration above 2k feet of northern Kauai and the mainly the
windward side of the Koolau Mountains on Oahu. This AIRMET will
likely stay in place overnight. AIRMET Sierra may spread to other
islands as well. Tops of these showers are between 8 and 10k feet.

Light rime icing remains a threat for Kauai and west of there as
the upper low, some 380 nm W of Kauai, continues to send dense
layered clouds over area. Will lower the flight levels to between
16 and 24k feet with the 10z package.

Otherwise, VFR condition continues.

&&

.MARINE...
A Gale Warning remains in effect for the Pailolo and Alenuihaha
Channels and waters south of the Big Island through early Thursday
morning due to the wind accelerations around the Big Island and
Maui. Small Craft Advisory (SCA) winds and seas for all other
Hawaiian waters will continue through Thursday night and
potentially through the upcoming weekend for windward waters and
channels. Winds and seas will begin to trend down late Thursday
through the weekend as strong high pressure to the northeast
weakens and low pressure to the northwest drifts away from the
state.

A High Surf Warning is in effect for exposed east facing shores
through early Thursday morning, which will shift to a High Surf
Advisory Thursday into the upcoming weekend due to the strong
winds locally and upstream over the past several days. The
downward trend will continue over the weekend, potentially
lowering below advisory levels by Sunday.

Surf along north facing shores will remain small through the rest of
the week and into the upcoming weekend. The split-flow upper pattern
across the northwest Pacific is responsible for this below average
spell for this time of year, which has pushed the storm track across
the far northwest Pacific from Japan to the Bering Sea and across
the far north-northeast Pacific from the eastern Aleutians to the
west coast. A mix of small west-northwest (300-320 deg) and
northerly (350-030 deg) swells from sources following these storm
tracks is expected by Sunday into early next week. A more sizable
northerly swell associated with low pressure dropping south-
southeast from the Aleutians across the northeast Pacific will be
possible Tuesday through midweek.

A small to moderate south swell (190 deg) will be possible over
the weekend due to a recent gale to storm-force low passing
southeast of New Zealand this past weekend. Seas associated with
this storm reached the 25-30 ft range, which was revealed in an
altimeter pass.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Thursday for most of the Hawaiian
Islands.

High Surf Advisory from 6 AM Thursday to 6 AM HST Friday for
Kauai Windward-Oahu Koolau-Olomana-Molokai Windward-Maui
Windward West-Windward Haleakala-South Big Island-Big Island
North and East.

High Surf Warning until 6 AM HST Thursday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Gale Warning until 6 AM HST Thursday for Pailolo Channel-
Alenuihaha Channel-Big Island Leeward Waters.

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-
Big Island Windward Waters-Big Island Southeast Waters.

&&

DISCUSSION...Bohlin
AVIATION...Lau
MARINE...Gibbs