Drought in Hawaii, December 1 to 31, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
901 PM HST Sat Nov 30 2019

.SYNOPSIS...
Gusty trade winds and high clouds will remain through the
weekend. A cloud band riding in on the trade winds will bring
cooler, wet weather tonight into Sunday, especially for windward
and mountain areas. More typical trade wind weather will return
Sunday night and continue through much of the upcoming work week,
with mainly windward and mauka showers and the occasional leeward
spillover. Trade winds will ease to moderate levels Monday and
Tuesday, then pick back up into the moderate and locally breezy
range late Wednesday through the end of the work week.

&&

.DISCUSSION...
Currently at the surface, a 1034 mb high centered around 1050
miles north-northwest of Honolulu, is driving breezy to windy
trades across the island chain this evening. Infrared satellite
imagery shows mostly cloudy skies across the state, with a 100 to
150 mile wide cloud band associated with an old front, evident
beneath a high cloud deck over and just north of the islands. The
cloud band has moved into Kauai this evening, where radar imagery
shows scattered to numerous showers streaming into windward
areas. The main cloud band and more numerous showers remains just
to the north of Oahu and Maui County, and still a ways north of
the Big Island. Main short term concerns revolve around trade
wind and rainfall trends with the band of low clouds and showers
moving through the state.

Tonight through Sunday night,
The band of low clouds and showers will sink steadily southward
through the islands tonight and Sunday, bringing windy and wet
weather to the entire island chain. Showers will be most frequent
over windward and mauka areas, but quite a bit of shower activity
will affect leeward locales as well. The brunt of the shower
activity should occur before noon Sunday across the smaller
islands, with drier air and less shower activity working in for
the afternoon. The drier air will likely take until Sunday
evening to work into the Big Island however. Fairly typical trade
wind weather should then prevail behind the cloud band, with
mainly windward and mauka showers and the occasional leeward
spillover. A Wind Advisory remains in effect for the typically
windier areas across the Big Island and Maui County. The trades
are expected to peak tonight into Sunday, so we will likely need
to extend the Wind Advisory through Sunday, and may also need to
expand the advisory to include other areas. Will monitor
observations closely through the night and make a decision on the
Wind Advisory with the morning forecast package. The trades are
expected to ease a bit Sunday night, but breezy conditions will
likely continue.

Monday through next Saturday,
High pressure north of the state will get reinforced by a new
and stronger high building to the northwest of the islands Monday
through Wednesday. This new high will then gradually weaken as it
shifts southeastward, well to the north and northeast of the
islands through the rest of the week. Moderate to breezy trades
should prevail through the period, although a brief easing into
the moderate range is expected Monday night into Wednesday and
again next Saturday.

As for weather details, a fairly typical trade wind pattern
should prevail through the work week and into next weekend,
featuring windward and mauka showers and the occasional leeward
spillover. There could be a bit of an increase in shower coverage
and intensity Monday night and Tuesday, and again Thursday night
through Friday night as upper level disturbances move overhead and
give a boost to the inversion heights.

&&

.AVIATION...
A band of clouds and showers associated with an old frontal
boundary will move through from north to south overnight into
Sunday morning. Windy and showery conditions are expected through
this time. Expect periodic MVFR conditions in low clouds/showers,
especially along the windward slopes. AIRMET SIERRA is now in
effect for north thru east sections of Kauai above 1000 feet due
to mountain obscuration from low clouds and showers. This will
likely need to be expanded down the island chain overnight into
Sunday as this band of clouds and showers moves in.

AIRMET TANGO remains in effect over and immediately south thru
west of mountains on all islands below 9000 feet due to tempo
moderate turbulence.

Although conditions should gradually improve through the day
Sunday (especially over the western end of the state) as this band
of clouds and showers continues southward, strong trades will
hold as high pressure builds to the north in its wake.

&&

.MARINE...
Strong surface high pressure is centered far north-northwest of
the state, while a gale low pressure system is located far
northeast of the islands. The strong northerly flow between these
features will push a remnant frontal boundary down over the
coastal waters through early Sunday morning. As a result, expect
strengthening northeast to east trade winds, and building, rough
seas. The winds may approach gale force in some of the typical
windier waters, such as the Alenuihaha and Pailolo Channels later
tonight and Sunday. Therefore, a Small Craft Advisory (SCA)
remains in effect through Sunday night for all Hawaiian waters.
The latest guidance suggests winds holding in the strong near
gale speeds through Sunday, and slowly weakening Sunday night.
Winds should continue to gradually weaken from Monday through
Tuesday as the high weakens north of the area due to a passing
front.

The captured fetch associated with the low pressure system,
combined with a broad area of strong northerly flow between the
high and the low is sending a large, long-period north swell into
the state. This swell is already being observed at NDBC buoy
51000 located north of the islands. The significant wave height
at the PacIOOS Waimea Bay buoy has recently spiked to 12 feet. A
combination of the long-period north swell, increasing trade wind
waves, and a short-period northeast swell will produce elevated,
rough surf along north and east facing shores into Monday. The
large north swell is expected to steadily fill in late tonight,
and peak Sunday or Sunday night. Surf may approach the High Surf
Warning criteria along some north facing shores. Strong trades
locally and upstream of the state will also bring rising surf
along east facing shores tonight, and will hold steady through
Sunday night. Surf will be locally higher for east facing shore
lines with a north exposure due to the large north swell. As a
result, a High Surf Advisory (HSA) remains in effect through
early Monday morning for north and east facing shores of Niihau,
Kauai, Oahu, Molokai, Maui, and Big Island. The HSA will likely
need to be extended through the day on Monday.

The large north and northeast swells will likely produce harbor
surges and large breaking waves near the entrances at Hilo and
Kahului Harbors into Monday. The surges may also cause overwash
at Bayfront Highway in Hilo. A Marine Weather Statement has been
issued to alert mariners in these north facing harbors about
these impacts. In addition, the swells may also result in
overwash and beach erosion along some vulnerable shore lines.

South facing shores will continue to receive small, mainly
background south swells into Sunday, with a slightly larger,
long-period south swell expected from Sunday night through
Tuesday. Some exposed south facing shores may receive wrap from
the large trade wind generated waves into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Olomana-
Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 6 AM HST Sunday for Lanai-Kahoolawe-Maui
Central Valley-Big Island North and East-Kohala.

Small Craft Advisory until 6 AM HST Monday for all Hawaiian
waters-

&&

DISCUSSION...Jelsema
AVIATION...Gibbs
MARINE...Houston