High Surf in Hawaii, July 25 to 27, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
453 PM HST Sat Jul 25 2020

.SYNOPSIS...
A trade wind weather pattern is expected through early tonight
thanks to high pressure far north of the state. Clouds and passing
showers will tend to favor windward and Mauka areas. Hurricane
Douglas is expected to pass near or over portions of the main
Hawaiian islands later tonight through early Monday with
deteriorating weather conditions expected across portions of the
state. Once Douglas departs the area, high pressure to our north
will allow for a trade wind weather pattern to return.

&&

.DISCUSSION...
Breezy trade wind weather can be expected through early tonight
as high pressure lies north of the area. Clouds and passing
showers will tend to favor windward and mauka areas with a few
brief showers possible over select leeward locations.

The weather scenario from later tonight through Monday time
period will be highly dependent on the size, track and intensity
of Hurricane Douglas. Weather conditions are expected to
deteriorate from east to west as Douglas passes near or over
portions of the main Hawaiian islands.

A Flash Flood Watch is currently in effect for all Hawaiian
islands through Monday. For all other watches, warnings and
potential impacts from Hurricane Douglas, please refer to the
latest Hurricane Local Statement (HLSHFO).

The latest forecast track has the center of Douglas passing just
north of the Big Island late tonight and Sunday morning, Maui
during the day Sunday, Oahu Sunday evening and Sunday night, then
near Kauai late Sunday night and Monday morning. Remember, impacts
can be realized well away from the center of the storm.

Once Douglas moves west of the main Hawaiian islands, a typical
trade wind weather pattern is expected to return thanks to high
pressure north of the area. Clouds and passing showers will favor
windward and mauka areas.

&&

.AVIATION...
Moderate to breezy trades will continue over western end of the
state tonight, while changes are in store for the eastern end.

Kauai and Oahu will remain predominantly VFR tonight, with some
brief MVFR conditions due to clouds and showers riding in on the
trade winds.

Tropical Cyclone Douglas is expected to enter the waters near the
Big Island tonight, and impacts from Douglas will felt over and
near the Big Island and Maui County through the night. As Douglas
moves closer to the islands, expect an increase in clouds, rain,
and wind. AIRMETs for IFR or mountain obscuration conditions, are
likely, as are AIRMETS for strong surface winds/turbulence. Effects
from Douglas are expected to spread to Kauai and Oahu Sunday.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the terrain of all islands, and will likely
continue into tonight. An AIRMET for strong surface winds may be
needed by the end of tonight for winds associated with Douglas.

No other AIRMETs are currently in effect. AIRMETs will likely be
needed for IFR/mountain obscuration as clouds and rain associated
with Douglas reach the islands.

&&

.MARINE...
A surface high north of the area will maintain moderate to locally
strong trade winds through this evening. While the winds drop off
for waters south of the Big Island tonight, seas will remain
above the 10-foot Small Craft Advisory (SCA) threshold due to
Hurricane Douglas. Therefore, the SCA has been extended through
tonight for that zone.

Winds will become much stronger as Hurricane Douglas approaches
from the east. A Hurricane Warning remains in effect for the Big
Island and Maui County Windward Waters, and has been expanded to
include the Oahu Windward Waters, as well as the Kaiwi and Kauai
channels. A Tropical Storm Warning remains in effect for the
Alenuihaha Channel, the Leeward Big Island Waters, and the remaining
waters surrounding Maui County, and has been expanded to include
the Leeward Oahu Waters. A Hurricane Watch remains in effect for
most leeward Hawaiian waters from Maui County to Oahu. Finally, a
Tropical Storm Watch remains in effect for the waters surrounding
Kauai. See the latest advisory from the Central Pacific Hurricane
Center in Honolulu for additional information on Douglas.

The very large swell from Hurricane Douglas is beginning to arrive
along east facing shores of the Big Island and Maui County, and
will continue to build there and on the remaining islands tonight
through Sunday. Very large and dangerous surf is expected, so a
High Surf Warning (HSW) is in effect for east facing shores of the
Big Island, Maui, Molokai and Kahoolawe. Hazardous surf is also
possible along the north facing shores of these islands that are
exposed to the east swell and wind waves. East facing shores of
Kauai and Oahu have now been added to the HSW beginning Sunday
morning. In addition to the life-threatening surf, ocean water
will likely surge over some parts of the coastline. This may cause
damage to roadways and other coastal infrastructure, especially
during high tide this evening and Sunday morning.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Hurricane Warning for Oahu.

Flash Flood Watch from Sunday morning through Monday afternoon
for Niihau-Kauai-Oahu.

Tropical Storm Warning for Niihau-Kauai-Molokai-Lanai-Kahoolawe-
Maui-Big Island.

High Surf Warning from 6 AM Sunday to 6 PM HST Monday for Kauai
Windward-Oahu Koolau-Olomana.

Hurricane Watch for Molokai-Lanai-Kahoolawe-Maui-Big Island.

Flash Flood Watch through Monday afternoon for Molokai-Lanai-
Kahoolawe-Maui-Big Island.

High Surf Warning until 6 AM HST Monday for Molokai Windward-
Kahoolawe-Maui Windward West-Windward Haleakala-Leeward
Haleakala-South Big Island-Big Island North and East.

Hurricane Warning for Kauai Channel-Oahu Windward Waters-Kaiwi
Channel-Maui County Windward Waters-Big Island Windward Waters.

Tropical Storm Warning for Kauai Northwest Waters-Kauai Windward
Waters-Kauai Leeward Waters-Oahu Leeward Waters-Maui County
Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-
Big Island Leeward Waters.

Hurricane Watch for Oahu Leeward Waters-Maui County Leeward
Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters.

Small Craft Advisory until 6 AM HST Sunday for Big Island
Southeast Waters.

&&

DISCUSSION...Burke
AVIATION...M Ballard
MARINE...TS