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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 150635
Area Forecast Discussion
National Weather Service Honolulu HI
835 PM HST Sun Aug 14 2022
Expect light to moderate trade winds as a long wave trough far
north of the state breaks down the ridge and decreases the trade
winds across the region. A hybrid wind pattern will develop on
Monday and Tuesday with leeward sea breezes and lighter easterly
trade winds lingering over windward areas. The high pressure ridge
builds back in north of the islands on Wednesday with
strengthening trade winds from Wednesday onward.
Satellite imagery this evening shows a few bands of clouds
drifting into each island on the trade winds. A low level trough
remains roughly 300 miles southeast of the Big Island, drifting
slowly westward on the trade winds. This trough may bring a slight
increase in showers over the eastern islands on Tuesday as it
passes south of the state. A few high cirrus clouds are drifting
over the islands associated with a weak subtropical jet stream.
A long wave trough far north of the state is breaking down the
subtropical ridge north of the islands and decreasing the trade
wind flow over the next three days. As these large scale winds
weaken, local scale land and sea breezes will strengthen from
Monday into Wednesday. This trough will weaken and drift further
eastward by Wednesday, allowing the ridge north of the islands to
build back in and cause the trade winds to strengthen across the
region. This translates to a hybrid wind pattern for the next
three days with land and sea breezes over leeward areas and light
trade winds over the windward zones. Clouds and a few showers will
tend to favor afternoons along convergence areas between the trade
winds and sea breezes over leeward areas and island interior
sections. Brief showers are also possible in this hybrid wind
pattern over windward zones in the overnight to early morning
hours. A minor wrinkle to this forecast is a passing low level
trough drifting south of the state on Tuesday and Wednesday.
Moisture around the eastern side of this trough may slightly
increase clouds and shower activity over the Big Island and Maui.
Chances for thunderstorms pick up over the higher elevations of
the Big Island from Wednesday afternoon to evening as surface
heating may trigger deeper convection or thunderstorms in the
unstable layer above the trade wind inversion height.
We transition back to a trade wind pattern on Wednesday as the
high pressure ridge begins to build back in north of the region.
Expect moderate to locally breezy trade winds from Thursday
through Sunday with diminishing land and sea breezes. Clouds and
brief passing showers will trend back towards the windward and
mountain sections of each island.
.AVIATION...Light to locally moderate trade winds will persist
through twenty-four hours and beyond. Ragged bands of
stratocumulus and light showers will favor east and northeast
facing slopes and coasts. A small eddy just west of the Big Island
may keep leeward Big Island shrouded overnight in VFR cloudiness
and promote afternoon sea breezes along the Kona Coast.
A trade wind inversion around 08 kft will inhibit daytime shower
development over island interiors, but brief moderate to heavy
showers will still be possible over interior Big Island in the
late afternoon and early evening.
Localized MVFR CIG or VIS possible in showers, otherwise VFR
conditions will prevail all areas. No AIRMETS are currently in
effect and none are expected through the forecast period.
Moderate to fresh easterly trades will hold tonight, then ease
into the gentle to moderate category Monday through Wednesday, as
the ridge north of the state weakens. This pattern will translate
to localized overnight land breezes and daytime sea breezes near
the coasts beginning by Monday afternoon. As typically observed
with these patterns, pockets of fresh breezes near some coasts can
lead to choppy conditions due to a combination of daytime heating
and terrain-induced accelerations. A return of fresh to strong
easterly trades is expected through the second half of the week as
the ridge builds to the north, which may lead to Small Craft
Advisory conditions for the windier waters and channels over the
eastern end of the state.
After a quiet spell through the first half of August, a more
active pattern unfolding within Hawaii's swell window around New
Zealand will lead to an upward trend along south facing shores
beginning next weekend. Until then, expect small conditions to
persist with mainly a combination of background south and
southeasterly energy moving through.
Surf along east facing shores will remain small through the first
half of the week as the aforementioned trades ease. A return of
choppy/short-period surf is expected by the end of the week as
the trades fill back in from east to west.
Surf along north facing shores will trend up slightly late
tonight into Monday at spots that favor northerly swells due to a
recent batch of northerly winds associated with low pressure
near/over the Aleutians aimed at us. This will be short-lived,
but may return to similar levels Wednesday night through Thursday
as a similar scenario unfolds tonight through Monday far north of
the area. Otherwise, the flat summertime conditions will prevail.
Large daily tide cycles associated with our typically observed
King Tides for this time of year will continue into Monday, then
steadily lower through the week.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office