Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 251947
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
947 AM HST WED MAY 25 2016

.SYNOPSIS...
A trough aloft will make the atmosphere unstable today...producing
heavy showers and a slight chance of thunderstorms through this
evening. The trough will also keep the winds lighter than normal
through next week. Gentle trade winds will continue most of the
time...but daytime sea breezes and nighttime land breezes will
prevail this weekend.

&&

.DISCUSSION...
Surface analyses show a 1031 MB surface high about 1900 miles
northeast of the islands and a 1028 MB high about 1350 miles to
the northwest. A front has moved south between the two highs to
about 500 miles north of the islands. A deep long-wave trough
runs from a low aloft near 44N 155W over the main Hawaiian
Islands. Trade winds persist over the main Hawaiian Islands but
the winds are lighter than normal since the front has made a large
dent in the subtropical ridge between the two highs. A short-wave
trough moving eastward through the bottom of the long-wave trough
has made the atmosphere over the islands unstable. Instability
from the trough and moisture from a low-cloud band moving over the
islands will combine to produce heavy showers and a slight chance
of thunderstorms over the islands through this evening. There is
also a possibility of snow showers over the summits of Mauna Kea
and Mauna Loa . The atmosphere will become more stable starting
tonight as the short- wave moves off to the northeast.

The winds will become even lighter through the weekend as a
surface trough forms over the islands. Daytime sea breezes will
produce clouds and showers over interior and leeward areas while
nighttime land breezes will bring partial clearing at night. The
light winds will allow emissions from Kilauea to spread over the
smaller islands.

Trade winds will return starting on Memorial Day as the surface
ridge rebuilds north of the islands. The trades may remain lighter
than normal through next week since the trough aloft will keep the
subtropical ridge weak.

&&

.AVIATION...
Frequent MVFR conditions and isolated IFR conditions are expected
today due to potentially slow moving and locally heavy showers.
These showers are the result of an area of low-level moisture over
the state and an upper level trough approaching from the
northwest. Many of the islands have been primarily VFR to start
the day, but clouds and showers will develop across interior
sections by afternoon. The exception is across eastern Maui, where
persistent showers and low ceilings have led to continued mountain
obscurations. The current AIRMET for mountain obscuration on Maui
may need to be expanded during the afternoon to cover additional
islands. Due to the instability associated with the approaching
upper level trough, there is also a slight chance of thunderstorms
during the afternoon.

Wind shear associated with the upper level trough may lead to
some high level clear air turbulence today. Model guidance
indicates that the potential for turbulence will diminish through
the afternoon and evening.

&&


.MARINE...
Gentle winds and moderate swells are expected through next week,
so no small-craft-advisory conditions are expected.

A moderate southwest swell from the Tasman sea is expected to
arrive late today, peak late Thursday and Friday, then decline
during the weekend. Since there are so many islands along the path
of the swell, surf is likely to be inconsistent. See the the
Collaborative Nearshore Swell and Wind Forecast (SRDHFO) for
details on this swell. Otherwise rather small surf is expected.

&&

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

&&

$$
Donaldson



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