Heavy Rain in Hawaii, July 2 to 3, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
923 AM HST Mon Jul 2 2018

.SYNOPSIS...
Trade winds will gradually increase today as high pressure builds
north of the state. Showers will remain focused over windward
slopes, with spotty heavy showers possible over leeward and interior
sections of the Big Island. A breezy trade wind regime will develop
and persist from Tuesday through the weekend. An increase in
rainfall is expected late Thursday possibly through the weekend.

&&

.DISCUSSION...
The forecast was recently updated to reflect thunderstorms on the
Big Island south of Pahoa, including Leilani Estates and other
areas near the coastline. Have received a couple reports of
thunder, and the lightning network is reporting several strikes.
Satellite and radar data shows cloud tops in the region reaching
near 36,000 feet. Anticipate thunderstorm activity to die off
later this afternoon, so have only added thunderstorms in for
today.

High pressure to the far north-northeast of the state will allow
trades to continue to build back in today. A dissipating upper
level low about 370 miles north of Hilo this morning continues to
drag a few high clouds over the eastern side of the Big Island,
but should dissipate and/or move to the east as the day wears on.
The associated upper level trough is closet to the Big Island,
delaying the trade wind return a bit.

The trough will continue to bring some shower activity to
additional areas of the Big Island, along with the possibility of
some heavy showers. As the trades become more established
statewide, expect the shower activity to become focused over the
typical windward and mountain locations.

Trades are expected to become locally breezy by Tuesday, and then
persist at similar levels into the weekend with a strong high
pressure far north of the islands with stable conditions over the
islands. Expect a breezy trade wind weather regime to reign, with
clouds and showers focusing along windward slopes into the
upcoming weekend. Winds may become strong enough to carry low
clouds and showers to lee areas of the smaller islands at times.
An increase in low level moisture and associated shower activity
is still expected from late Thursday possibly through the weekend.

&&

.AVIATION...
VFR will prevail over most areas through the day. Areas of denser
cloudiness and precipitation (brief MVFR) will occur over
windward and mauka sections at times as trade winds gradually
strengthen.

Specifically for the Big Island, an area of moisture that has
moved up from the southeast and south, coupled with an upper
level trough over the eastern part of the state, may bring more
widespread precipitation (and MVFR conditions) today, especially
over interior sections and leeward slopes this afternoon. Isolated
thunderstorms are also possible over the Big Island today,
including a nearly stationary cell currently over the Kapoho
area. Some of this moisture may eventually affect Maui as well.

An area of clouds and showers is moving out of Kauai, so AIRMET
Sierra for mountain obscuration is cancelled. An additional
AIRMET for mountain obscuration may be needed this afternoon if
shower/thunderstorm activity on the Big Island becomes extensive
enough.

&&

.MARINE...
High pressure far NNE of the state will move slowly westward and
strengthen during the next few days. This will cause trade winds
to gradually increase across the area. A Small Craft Advisory is
posted for the typically windy waters around Maui County and the
Big Island. Trade winds are expected to increase a bit more later
in the week as the pressure gradient tightens across the area.
This may cause the the advisory to be expanded to other parts of
the coastal waters.

A series of small, to briefly moderate size southerly swells, can
be expected through the week and into the weekend. Strengthening
trade winds will cause a gradual increase in short period choppy
surf along east facing shores. This combined with a longer period
east swell from distant Tropical Cyclone Fabio in the Eastern
Pacific may cause surf to reach High Surf Advisory levels on east
facing shores later this week and into the weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

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