Drought in Hawaii, June 11 to 30, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
815 PM HST Mon Jun 10 2019

.SYNOPSIS...
Expect a slight increase to the easterly trade winds on Tuesday
with modified sea breezes lingering over sheltered western slopes
of all islands. Stable conditions will keep shower activity to
a minimum through much of the week. Increasing moisture levels on
Friday and Saturday may bring a brief period of elevated clouds
and showers to the state.

&&

.DISCUSSION...
Satellite imagery this evening shows a few bands of mostly stable
low clouds drifting through the region with the light easterly
trade wind flow. Light winds will continue tonight with a slight
increase in easterly trade wind flow on Tuesday.

No changes to the large scale pressure pattern. A high pressure
system anchored off the west coast of the U.S. will interact with
a long wave trough over the Central Pacific, keeping the Hawaiian
Islands along the southwestern edge of the subtropical ridge.
Surface pressure gradients will increase a bit on Tuesday allowing
easterly winds to increase into the moderate to locally breezy
range. Sea breezes will be pushed back into the more sheltered
western slopes of each island. These moderate trade winds will
continue across all islands through next weekend.

In the upper levels, a high pressure ridge aloft will keep shower
activity to a minimum on Tuesday. This upper ridge weakens a bit
on Wednesday and Thursday, as a short wave trough passes north of
the state, possibly elevating some windward and mauka showers in
the overnight and early morning time periods.

The latest long range model guidance is changing. Both the
American (GFS) model and the European (ECMWF) model are showing
an unstable moisture plume moving up from the deep tropics.
This additional moisture will then drift into the islands from
the southeast direction on Friday and Saturday. Precipitable water
levels will range from 1.0 to 2.0 inches in a north to south
gradient. Deep easterly wind flow up through 25,000 feet will also
favor higher shower trends across the state. Chances for
precipitation were increased this afternoon for the Friday night
to Saturday afternoon time periods. While both models are showing
increasing moisture trends, the ECMWF model brings the moisture
further north than the GFS, which if the European model is right
will bring a wetter solution to the northwestern islands. Expect
continued changes to the precipitation forecast for Friday and
Saturday as this weather pattern evolves over time.

&&

.AVIATION...
A strengthening ridge of high pressure far north of the islands
will bring a small boost in the trades to locally strong on
Tuesday. This might warrant AIRMET Tango for low level turbulence
over and lee of mountain ranges of all islands. But for now, the
trades are relatively light, and turbulence is not an issue.

There are some widely scattered showers embedded in this trade
wind flow. These showers will bring brief MVFR ceilings and vis
to the windward and mountain areas of all islands, but especially
windward areas of Maui and the Big Island. Thus far, these cloud
and showers are not a threat to lead to an AIRMET Sierra for
mountain obscuration. A few late night showers may pop up along
and over the adjacent waters of the Big Island's leeward coast.
Otherwise, VFR conditions prevails.

&&

.MARINE...
A stalled front about 350 miles NW of Kauai continues to keep the
trade wind supporting surface ridge suppressed southward from its
climatological position. Forecast models indicate little overall
change to this pattern over the next several days, with moderate
to locally fresh trade winds over Maui county and Big Island
waters, and gentle to moderate trade winds over Kauai and Oahu
waters. Whether or not the flow is accelerated to the point that
a Small Craft Advisory is required for the windier zones remains
uncertain, and observations will be monitored.

While surf is expected to remain below advisory levels along all
shores for most of the upcoming week, it won't be flat. Surf will
be dropping along N facing shores Tuesday and Wednesday, but small
NW swells arriving from Thursday into the weekend will once again
support small surf along N and W facing shores. A small SSW will
linger for the next couple of days, providing small waves to
exposed S and W facing shores. The fetch of trade winds near and
upstream of the islands contains lighter than normal winds, with
relatively small wind waves supporting small surf along E facing
shores. A significant long-period S swell is expected toward the
end of the week and into the weekend, and may produce advisory
level surf to S facing shores as it peaks Friday/Saturday.

&&

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

&&

DISCUSSION...Bohlin
AVIATION...Lau
MARINE...Birchard