Drought in Hawaii, August 29 to 31, 2017

Area Forecast Discussion...Corrected
National Weather Service Honolulu HI
830 PM HST Mon Aug 28 2017

.SYNOPSIS...
Trade winds will continue in the light to locally moderate range for
the next few days as a weak ridge of high pressure lies a few
hundred miles north of the state. Clouds and passing showers will
favor windward and mauka areas with some afternoon clouds and
showers possible over interior areas. Winds will become lighter by
the weekend as a front approaches the area from the northwest.
Showers will tend to favor interior and lee areas during the
afternoon hours with still some passing showers possible along
windward areas.

&&

.DISCUSSION...
Localized heavy rain has developed over windward Oahu this evening,
with radar indicating rain rate of a quarter to slightly over half
an inch per hour in the last hour. This is a result of a line of
clouds embedded in trade winds reaching Oahu while the airmass is
slightly unstable airmass due to the present of an upper level
trough just northeast of the islands. Latest satellite imagery
indicated there are still more low clouds just east of Oahu at this
time, therefore expect more rain to affect windward Oahu through
rest of the evening. This line of low clouds is now aligned more
toward Kauai at this time. Thus windward Kauai will probably see an
increase in rainfall as the night progresses. Meanwhile, there are
patches of low clouds reaching windward Big Island. These clouds
will bring measurable precipitation for the windward Big Island
through the rest of the evening into early Tuesday. Maui county
is experiencing mainly fair weather so far this evening, though
shall not be surprised if some moisture will reach windward
Maui and Molokai overnight.

A pair of high pressure centers continued to center to the far
northeast and northwest of the state with an east to west oriented
ridge between them. As the ridge being only a few hundred miles
to our north, pressure gradient is not strong across the area,
resulting trade winds staying in the light to locally moderate
range across the islands. It will be uneventful trade wind weather
if not for the moisture moving across the islands as well as the
present of the aforementioned upper level feature just northeast of
the state. With dew points in the upper 60s to low 70s, rather muggy
conditions will prevail through Tuesday. Moreover, locally heavier
rainfall is possible as the airmass will remain slightly unstable in
the mean time. Expect the weather conditions to improve slightly by
Wednesday as the moisture exits east. Meanwhile, the upper level
feature will lift north late Wednesday into Thursday, allowing the
airmass in the island vicinity to become more stable.

As we head into the weekend onto early next week, a front from the
northwest is forecast to advance toward the islands, nudging the
surface ridge north of the area a bit closer to the state. The
result will be winds becoming light across the area with daytime sea
breezes and nighttime land breezes becoming more prominent. Forecast
guidance also indicated a drier airmass may move in from the east,
leading to possible less muggy sensible weather. Clouds and showers
will tend to form due to daytime heating with the highest chances
for showers being over interior areas. Instability will be limited
so hydrologic concern from the showers will be low.

&&

.AVIATION...
Enhanced moisture will continue to move through the central
islands tonight, aiding in producing showers with MVFR conditions.
AIRMET SIERRA for mountain obscuration is posted for the north
through east facing slopes Oahu this evening. This will be updated
as needed through rest of the evening into early Tuesday morning.
Otherwise, VFR conditions should prevail. Light to locally moderate
trade winds will continue across the state with localized land
breezes forming across select leeward areas overnight.

&&

.MARINE...
Weak ridging north of the islands will maintain mainly moderate
trades through the rest of the week. The trades may turn even
lighter on Friday and over the weekend as an out-of-season front
nudges a surface ridge down close to the islands.

A series of small swell from the southeast and southwest will
dominate the surf along the south facing shores the first half of
the work week. Then, a long period south swell of up to 4 feet 15 to
17 seconds arrive late Wednesday, peak on Thursday, and continue
through Saturday before lowering to 3 feet Sunday. This swell may
warrant a High Surf Advisory for the south facing shores.

Due to the soft trades, surf along the east facing shores will be
relatively small that may become even smaller over the latter part of
the week as the trades weaken further.

&&

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

&&

Hui/Lau