High Surf in Hawaii, May 11 to 13, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
341 AM HST Sat May 11 2019

.SYNOPSIS...
A ridge of high pressure northwest of the islands will maintain
a gentle trade wind flow through the rest of the weekend. A weak
surface trough is expected to bring an uptick in showers to
especially the eastern islands Saturday night through Tuesday.
A passing upper level disturbance will help enhance some of these
showers between Sunday and Tuesday. Strengthening high pressure
toward the middle of next week will bring a boost in the trade
winds to locally strong.

&&

.DISCUSSION...
Clouds and showers picked up in the evening as an area of clouds
with embedded showers blew through. As of 3 am HST, most of the
showers have gone by, although some bit of cloudiness still remains.
These clouds are expected to thin out later this morning,
resulting in fairly descent afternoon.

The gentle trades on tap for today will promote locally daytime
sea breezes that will lead to some interior and leeward cloudiness
in the afternoon hours. A stable air mass, though, will limit the
showers to isolated.

A change is then coming.

A weak, surface trough, marked by an area of clouds on satellite,
about 100 miles east of Cape Kumukahi, Big Island, is moving
slowly west with the trade wind flow. We expect the bulk of the
moisture to move across windward Big Island tonight, and onto
Maui on Sunday. Some of this moisture will continue on to the
remaining islands downwind, but windward Maui and the Big Island
will be impacted the most. The surface trough is expected to
dissipate when it reaches Maui on Sunday. Between Sunday and
Monday, a passing upper level disturbance will help enhancement
the shower-bearing clouds beneath. Leeward Big Island will see an
uptick in showers both Sunday and Monday afternoons as well.
This moisture field and lingering instability may linger into
Tuesday.

Upper ridging will begin building across the area Tuesday night,
causing a strengthening of surface high pressure passing north of
the islands. This will result in a boost in the trades to locally
strong and more stable air mass.

&&

.AVIATION...
A light to occasional moderate trade wind pattern will allow
continued land and sea breezes to develop along the leeward coasts
over the next 24 hours. Wind directions along the boundaries
between light northeast trade winds and sea breezes will produce
erratic wind directions at times for some leeward airfields.
Cloud ceilings will develop over mountains and island interior
sections from afternoon through early evening. Isolated to
scattered showers are possible along with brief periods of MVFR
ceilings.

AIRMET Sierra in effect for tempo mountain obscuration over
portions of Kauai and Oahu. This AIRMET will likely be cancelled
by 16Z.

&&

.MARINE...
Light trade winds will prevail over the coastal waters through
the weekend. High pressure will build in from the northwest and
trade winds will gradually strengthen starting Monday. The
typically windier waters around Maui County and the Big Island
could see Small Craft Advisory winds by midweek. As the trade
winds strengthen next week, so should surf along east facing
shores.

A short period northwest swell will decline through the rest of
the weekend. A series of long period south swells will keep fun
surf along the south and west facing shores well into next week.
The largest of the south swells is forecast to build later today
and could produce surf near or at advisory levels for the south
facing shores Sunday into early next week. The current philosophy
keeps a 3 to 4 feet, 17-19 second south swell over most of the
area for Sunday and Monday. The south swell will gradually lower
through the first half of next week and remain small during the
second half of the week.

Small southeast swells will persist through the middle of next
week, but the Big Island will block some of the swell from
reaching the smaller islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

H Lau/Bohlin/Foster