Current Conditions
Temp0.5 C
RH95 %
WindNNW 10 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

015
FXHW60 PHFO 260125
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
325 PM HST WED MAY 25 2016

.SYNOPSIS...
A trough aloft will make the atmosphere unstable and produce
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 1033 MB surface high about 1900 miles
northeast of the islands and a 1026 MB high about 1200 miles to
the northwest. A front between the two highs extends 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 near
Molokai 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 later 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 will
continue into at least the early evening. Low level moisture is
greatest from Oahu to the Big Island, and showers and the most
widespread ceiling and visibility restrictions are located through
this area. Occasional MVFR conditions will also occur over Kauai,
but will diminish faster this evening. Water vapor imagery shows a
sharpening upper level trough swinging across the state, which
will continue to enhance convection. An AIRMET for mountain
obscuration is currently in effect from Oahu to the Big Island.
Conditions will begin to improve after sunset, but windward
sections may still hold onto some showers and MVFR conditions
overnight. Due to the existing instability and support from the
upper level trough, there is also a slight chance of thunderstorms
into the evening over the eastern half of the state.

Wind shear associated with the upper level trough may lead to
some high level clear air turbulence. Model guidance indicates
that the CAT potential has diminished and will continue to do so
through the evening. However, recent darkening/drying apparent in
water vapor imagery would indicate a greater turbulence
potential. Therefore we will hold onto the turbulence AIRMET for
now.

&&

.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.

&&

$$

AVIATION - Bravender
REST - Donaldson

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office