Heavy Rain in Hawaii, August 2, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
1220 AM HST Fri Aug 2 2019

.UPDATE...
No significant forecast changes in the 11 PM HST advisory for
Erick and Flossie. For the rest of the night, the threat for
heavy rain will continue over the southeast slopes and windward
areas of the Big Island where a Flash Flood Watch remains in
effect through the day Friday.

&&

.SYNOPSIS...
Gusty easterly winds will continue through Saturday as Tropical
Storm Erick passes south of the state. Deep tropical moisture
expected to move over the islands north of Erick will keep the rain
chances up, initially over the eastern portion of the state tonight,
then across the smaller islands Friday through Saturday. The best
chance for heavy rainfall and flash flooding will remain over Big
Island windward areas. 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.

&&

.PREV DISCUSSION.../ISSUED 825 PM HST Thu Aug 1 2019/
The subtropical ridge remains well north of the state, supporting
breezy trades over the region. 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
remain in place over the eastern end of the state tonight 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
through Saturday for the Big Island.

In addition to the tropical moisture and rainfall chances, gusty
easterly winds will continue through Saturday as Erick passes to the
south in response to the tight pressure gradient between Erick and
the subtropical ridge to the north. As a result, a Wind Advisory
remains in effect for Maui County and the Big Island through Friday.

Later this weekend through early next week, the focus will shift to
Tropical Storm Flossie, which is about 1350 miles east 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 combination, of high pressure ridging north of the islands
and low pressure in the form of ERICK to the south, is producing
breezy to strong trade winds across the area. Brief to TEMPO MVFR
conditions in passing showers will mainly affect windward and
mauka locales, with the Big Island and Maui likely seeing the
most precipitation through tonight into Friday.

AIRMET Tango remains 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 also in effect 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 to more isles later tonight
or Friday.

&&

.MARINE...
The Central Pacific Hurricane Center located here in Honolulu,
Hawaii is issuing advisories on Tropical Storm Erick, which is
centered about 155 nm south of South Point on the Big Island of
Hawaii early this evening. The latest forecast issued at 5 PM HST
indicates this system is expected to continue moving west-
northwestward south of the islands through Friday evening. The
radius of 34 kt or greater winds extend out up to 90 nm north of
the center. Therefore, a Tropical Storm Warning remains effect for
the coastal waters south of the Big Island. A Small Craft
Advisory (SCA) continues for the remaining coastal waters due to a
combination of strong winds and elevated, rough seas.

A High Surf Warning remains in effect through Friday afternoon
for east facing shores of the Big Island due to the large east-
southeast swell produced by Erick while it was hurricane.
Elsewhere, a High Surf Advisory also remains in effect through
Friday afternoon along east and south facing shores of Kauai and
Oahu, and for east facing shores of Maui.

The National Hurricane Center in Miami Florida is issuing
advisories on East Pacific Tropical Cyclone Flossie, which is
expected to cross longitude 140W into the central Pacific Friday
afternoon. The latest Wave Watch III model guidance indicates the
large swell produced by the captured fetch of Flossie may reach
east facing shores of the Big Island and Maui late Saturday night
or early Sunday. The latest forecast track has Flossie tracking
further north than Erick, which will likely allow less shadowing
of this swell along east facing shores of the smaller islands west
of Maui. This elevated surf is expected to persist from Sunday
through Monday night.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Friday for Kauai Windward-
Kauai Leeward-Oahu South Shore-Oahu Koolau-Olomana-Windward
Haleakala.

Flash Flood Watch through Saturday morning for Big Island.

Wind Advisory until 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 Friday 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...Gibbs
AVIATION...Kinel
MARINE...Houston