High Surf in Hawaii, August 1 to 6, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
946 AM HST Thu Aug 1 2019

.SYNOPSIS...
Breezy trades will hold through the morning hours today, then
increase this afternoon through Saturday as Hurricane Erick passes
south of the state. Deep tropical moisture expected to move over
the islands north of Erick will translate to increasing rainfall
chances, initially over the eastern portion of the state today,
then across the smaller islands tonight through Saturday. The best
chance for heavy rainfall and flash flooding will remain over the
Big Island windward areas through this time. Additional impacts
will include large seas and surf for the exposed coasts. Later
this weekend through early next week, Tropical Storm Flossie will
approach and could bring additional impacts to the islands.

&&

.DISCUSSION...
The subtropical ridge remains well north of the state, supporting
breezy trades over the region. Winds and shower coverage
increased a bit overnight, especially across the eastern end of
the state. The morning Hilo sounding reflected why, with PW
nearing two inches, significantly higher than yesterday.

Models show the potential for a wet and windy period across the
islands as Erick passes to the south tonight through Saturday. The
threat for heavy rainfall will begin over the eastern end of the
state this afternoon through early Friday, then spread to the
smaller islands Friday through Saturday. Although the bulk of the
rainfall coverage will focus over windward areas, some will
manage to spill over into leeward sections of the smaller islands
due to the elevated inversion and strong easterly winds. The
greatest chance for flash flooding will remain over the windward
and southeast slopes of the Big Island through this time and a
Flash Flood Watch remains in effect from this afternoon through
Saturday for the Big Island.

Easterly winds will strengthen in response to a tightening
pressure gradient between Erick passing to the south and the
subtropical ridge to the north. As a result, a Wind Advisory
remains in effect for Maui County and the Big Island from this
afternoon through Friday.

Later this weekend through early next week, the focus will shift
to Tropical Storm Flossie, which is about 1500 miles east-
southeast of Hilo, Hawaii. The National Hurricane Center in Miami,
Florida, is issuing advisories on Flossie and shows the system
approaching the eastern end of the state late Sunday through
Tuesday on a weakening trend. Although forecast confidence is
steadily rising, it remains too early to determine or pin down any
impacts at this point.

&&

.AVIATION...
The pressure gradient between high pressure north of the state
and Tropical Cyclone Erick, will continue to produce rather strong
trade winds across the area. AIRMET Tango is posted for low level
turbulence below 8000 feet over and just downwind of terrain as
well as for localized strong surface winds.

AIRMET Sierra is posted for mountain obscuration along north
through east sections of the Big Island due to moisture associated
with Tropical Cyclone Erick interacting with island terrain. This
may need to be expanded elsewhere later today and tonight.

&&

.MARINE...
Hurricane Erick is about about 250 nm south-southeast of the Big
Island of Hawaii this morning and is expected to continue to move
to the west through the southern offshore waters through Friday
evening. A Hurricane Warning is in effect for the offshore waters
and a Tropical Storm Warning is in effect for the coastal waters
south of the Big Island. A Small Craft Advisory (SCA) continues
for the remaining coastal waters for a combination of SCA level
winds and seas.

A High Surf Warning is in effect for east facing shores of the Big
Island for large surf generated by Erick. An Isaac Hale morning
surf report was 18 feet, in line with what was expected. The Big
Island will block much of the swell generated by Erick from
reaching the smaller islands, but the strong trade winds will
maintain rough surf along east facing shores. As Erick passes
south of the Big Island, southeast swells from the system may
affect the smaller islands for a short time.

Have updated the surf values for the east and south facing shores
of Oahu due to the reports and buoy readings. The trade wind
swell is producing surf a little above what was originally
expected, and its expected to remain steady just below advisory
levels through Friday. The southeast swell generated by Erick is
reaching the Makapu Buoy near Oahu, so have boosted the surf along
south facing shores, but still expect a bump tomorrow as mentioned
above.

Tropical Cyclone Flossie is expected to cross from the East
Pacific into the Central Pacific basin as a hurricane late Friday
or Friday night. The current forecast track has Flossie tracking
further north than Erick. This will allow less shadowing for the
smaller islands and may bring higher surf later this weekend into
early next week along east facing shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from noon HST today through Saturday morning
for Big Island.

Wind Advisory from noon today to 6 PM HST Friday for Molokai
Windward-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-South
Big Island-Big Island North and East-Kohala-Big Island Interior.

High Surf Warning until 6 PM HST this evening for South Big
Island-Big Island North and East.

Tropical Storm Warning for Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM 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-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters.

&&

DISCUSSION...Powell
AVIATION...Burke
MARINE...M Ballard