Drought in Hawaii, December 1 to 15, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
836 PM HST Mon Nov 30 2020

.SYNOPSIS...
Light and variable winds remain in the forecast through Thursday
with brief periods of showers possible over island interior
sections each afternoon with cloud clearing each night. More
stable atmospheric conditions are expected through Wednesday with
higher shower trends on Thursday and Friday as a weakening front
will combine with additional moisture moving in from the east to
bring a period of increased shower coverage. Moderate to breezy
trade winds return by Friday, with lighter winds returning from
Saturday afternoon into Sunday.

&&

.DISCUSSION...
Satellite imagery this evening shows an upper level low roughly
300 miles east of the Big Island producing thunderstorms with
significant lighting activity far east of the state. A cold front
moving into the Central Pacific basin roughly 600 miles NW of
Kauai is slowly approaching the Hawaiian Islands with the arrival
of any shower impacts with this system likely delayed until the
Thursday. There is minimal cloud coverage near the islands tonight
due to an upper level ridge creating a more stable environment
along with light and variable winds. Local radar shows only
isolated showers mainly over the coastal waters near Kauai.

A cold front moving slowly through the Central Pacific north of
the state will keep the high pressure ridge near the islands in a
weakened state. This means that trade winds will diminish leading
to a light and variable wind regime. Local scale land and sea
breezes will continue in the absence of large scale winds. Onshore
daytime sea breezes, produced by solar heating of the land during
the day, will cause clouds to converge over island interior
sections with only brief period of showers mainly in the
afternoon hours. Offshore land breezes, driven by radiational
cooling of the land at night, will clear out clouds and showers
in the evening hours.

Bundle up. Drier air over the region will lead to cooler morning
low temperatures reaching the low to mid 60's through Wednesday
morning. Humidity levels will trend higher as additional moisture
moves in on Thursday and Friday from a shallow front moving in
from the north and a band of moisture drifting in from the east.
Morning low temperature will increase by a few degrees due to
these rising moisture levels. Shower activity will also increase
from Thursday onward due to the cloud band from the weakening
front and the return of moderate to breezy trades by Friday. Wind
speeds weaken once again from Saturday afternoon into Sunday as
yet another cold front moves in far north of the island chain.

&&

.AVIATION...
Land breezes will clear out remaining clouds over the islands
tonight leading to prevailing VFR areawide. Light winds will
continue through the forecast period allowing sea breezes and
subsequent inland cloud/shower development to take shape again on
Tuesday.

&&

.MARINE...
The first large northwest swell of the season is expected to
arrive Tuesday morning, with the first long period energy expected
to reach the buoys to the northwest shortly after daybreak. This
swell is expected to bring warning level surf by the
afternoon/evening hours, and persist into Thursday. Guidance
depicts a peak Tuesday night into Wednesday with surf likely
reaching the giant category (>40 ft) along exposed shores. Impacts
may include significant beach erosion with water sweeping across
beach areas that typically remain dry. The highest probability for
water reaching coastal roadways and property will be early
morning Wednesday as the swell and high tide coincide.

This large northwest swell will drive seas well above the 10 ft
Small Craft Advisory (SCA) threshold for waters exposed to
northwest swells. Expect the SCA to be posted with the morning
package for most waters, and expect seas to remain elevated into
Thursday.

Weakening trade winds will allow land and sea breeze regime
statewide through midweek as a series of fronts pass north of the
islands. Surf along east facing shores will drop through the first
half of the week as trade winds diminish. Fresh trades could
briefly return late in the week as a ridge noses eastward behind
one of the fronts.

Looking ahead, another significant swell event appears possible
early next week with models depicting a hurricane force low
developing far northwest of the islands Friday, and moving into
the central North Pacific Saturday. WAVEWATCH III and ensemble
wave data depict this storm producing a large swell arriving in
the islands Sunday night. Forecast confidence this far out remains
low and changes are likely in the coming days.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning from noon Tuesday to 6 PM HST Thursday for
north and west facing shores of Kauai Niihau Oahu Molokai and
Maui.

&&

DISCUSSION...Bohlin
AVIATION...JVC
MARINE...M Ballard