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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 150702
Area Forecast Discussion
National Weather Service Honolulu HI
902 PM HST Sun Oct 14 2018
A cloud band over Kauai will move southeast across Oahu and Maui
County tonight through Monday, then stall and dissipate over the
Big Island Tuesday. A high will build north of the area tonight
and persist through the week.
Satellite loops show a 90 mile wide band of showery low clouds running
east northeast to west southwest over Kauai. This band is associated
with the remnant of a front. Clouds associated with this band cover
Kauai and Niihau and the coastal waters around Kauai County. Clouds
are scattered over most areas from Oahu to the leeward side of the
Big Island of Hawaii with patchy broken low clouds over windward Oahu.
A trough extends northeast from over the Big Island. Broken to overcast
low clouds associated with the trough cover the coast and lower slopes
of the Big Island from Upolu Point to South Point and the coastal waters
east of the Big Island.
A surface ridge will build eastward north of the islands and moderate
northeast trade winds will spread over the islands. The cloud band
over Kauai will shift southeast slowly and weaken tomorrow, then
stall and dissipate near the Big Island. Clouds and showers in the
band will spread over Oahu and Maui tonight and tomorrow and reach
the Big Island Monday night. The cloud band is rather shallow, so
the showers in the band will affect mainly windward areas of the
smaller islands, with only isolated showers spreading to leeward
areas. A trough aloft is making the atmosphere less stable over
the Big Island with deeper moisture there. Showers will be more
active on the Big Island through tomorrow with some showers building
over interior and leeward slopes tomorrow afternoon. As the trough
aloft lifts north and weakens on Tuesday, the atmosphere over the
Big Island will become more stable.
From Wednesday through next weekend a surface ridge will persist
north of the main Hawaiian Islands and maintain moderate to
locally fresh northeast to east trade winds over the area. Ridging
aloft will keep the atmosphere rather dry and stable, so showers
will be focused over mainly windward areas with no heavy rainfall
expected. Leeward areas will remain mostly dry.
A diffuse frontal band continues to sag down across the central
islands this evening. The northerly low-level flow behind this
feature continues to produce overcast low clouds and frequent
showers along north facing sections of Kauai. As a result, AIRMET
Sierra remains in effect for mountain obscuration on that island.
This AIRMET may persist through daybreak Monday morning.
Elsewhere, broken to overcast low clouds and scattered showers
associated with this band will likely produce brief periods of
MVFR conditions over north and northeast facing slopes of most of
the smaller islands from Oahu to Maui through early Monday
morning. Otherwise, expect mainly VFR conditions to prevail over
the smaller islands.
Abundant moisture and a weak surface trough in the vicinity of
the eastern end of the state continue to generate low clouds and
showers over the southern and southeastern Big Island early this
evening. AIRMET Sierra also remains in effect for mountain
obscuration on that island from near Hilo to South Point. The low
clouds and showers associated with the frontal band may begin to
filter into the extreme northern end of the Big Island Monday
morning. This may cause brief periods of MVFR to develop.
AIRMET Tango for upper-level turbulence remains in effect over
Hawaii between FL260 and FL420. This AIRMET will likely remain in
effect through early Monday morning.
Looking ahead to daytime Monday, the front will likely stall near
Maui County before dawn Monday. The low-level flow is expected to
become northeasterly during the day on Monday. Drier air moving
into Kauai and Oahu may limit showers there after mid-morning
Monday. However, low clouds and showers will likely continue to
move into northeastern sections of the central Hawaiian islands,
which may result in brief periods of MVFR conditions through late
Monday afternoon. The surface trough near the Big Island is
expected to weaken by Monday, so conditions will likely improve
over the southeastern Big Island on Monday.
A weak front will stall across Maui County late tonight and
gradually dissipate on Monday, while a trough near the Big Island
falls apart. A surface ridge building north of the state will
drive gentle to moderate north to northeast winds tonight, with
moderate to locally fresh northeasterly trade winds settling over
the island chain on Monday. Winds will peak just below Small Craft
Advisory strength across Maui County waters Monday night and
Tuesday, followed by a slight decrease on Wednesday and Thursday.
An active surf pattern from the north and south is due this week.
A pulse of shorter period north-northwest swell will push north
shore surf to near October average tonight and early Monday. A
larger north-northwest swell will arrive on Tuesday. Resulting
surf will likely be well above the High Surf Advisory level for
north facing shores on Tuesday and Wednesday, and combined seas
over exposed waters may meet the 10 ft threshold for a Small
Craft Advisory a that time. This swell will gradually lower
Thursday and Friday and may be reinforced to around October
average for next weekend.
The run of late season south-southwest swells will continue
through the week. Another pulse is expected to fill in tonight
and hold through Monday, which will support moderate surf slightly
above the October average. A gradual downward trend from this
source is anticipated midweek. A larger south-southwest swell is
expected to fill in on Friday and produce High Surf Advisory level
surf through next weekend.
Surf along east facing shores will remain below October average
through the week, though a slight increase is due as winds pick up
during the next couple of days.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office