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Forecast Discussion for Honolulu, HI

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FXHW60 PHFO 100128

Area Forecast Discussion
National Weather Service Honolulu HI
328 PM HST Thu Apr 9 2020

Light and variable winds will persist through Friday, with clouds
and showers over the islands most likely in the afternoon and
evening. An increase in west to southwest winds is expected
Friday into Saturday as a front approaches from the northwest. The
front will bring a wind shift to the north, and a few showers, as
it moves down the island chain Saturday night and Sunday. Light
to moderate trade winds will begin to return late Sunday and
continue through much of next week.


Currently at the surface, high pressure systems are located far
to the west and northeast of the islands, with an area of low
pressure well to the north of the state. Closer to home, the
remnant moisture associated with a dissipated frontal boundary
resides over the eastern islands. The resulting pressure gradient
remains quite weak, with sea breezes in place state wide. Visible
satellite imagery shows partly to mostly cloudy conditions, with
cloud cover most prevalent over windward areas. Radar imagery
shows scattered showers over windward areas, with mainly rain
free conditions over leeward locales at the moment. Main short
term concern revolves around rain chances the next few days.

A light wind regime is expected to remain in place tonight,
with daytime sea breezes giving way to overnight land breezes. A
cold front will approach from the northwest Friday through
Saturday, bringing an increase in west to southwest winds. The
front will slide southeastward across the island chain late
Saturday through Sunday, with moderate north winds filling in
behind the front Saturday night and shifting around to
northeasterly trades on Sunday. High pressure will slide by to the
north of the islands Sunday night and Monday, with light to
moderate trades prevailing. The trades are expected to ease again
Monday night through Tuesday night as surface troughing develops
over the islands. Moderate trades are then expected to return
Wednesday and continue through late next week.

As for weather details, a sea/land breeze pattern is expected to
continue through Friday, with showers favoring interior mauka
areas during the afternoon/evening hours and locations near the
coast at night and during the morning hours. An approaching
shortwave trough may de-stabilize things enough for a thunderstorm
to pop over the Big Island Friday afternoon, so will mention a
slight chance of thunderstorms here. Shower coverage should
increase a bit Friday night and Saturday in the low level
convergent flow ahead of the approaching front, with assistance
from shortwave energy moving overhead. Showers will favor south
and southwest facing slopes at night and during the morning hours
and interior/mauka locations during the afternoon. A few showers
will accompany the front as it slides southeastward through the
islands Saturday night and Sunday, but no significant rainfall is
expected. We should begin to see an increase in trade wind showers
Sunday night and Monday, favoring the typical windward areas.
Shower coverage and intensity may then increase Monday night
through Tuesday night as surface troughing develops over the
islands and some shortwave energy moves overhead. A more typical
trade wind pattern should then return by the middle and latter
part of next week.


Sea breezes did not disappoint and have delivered an uptick in
cloud cover and showers over the Aloha State this afternoon. The
Big Island is seeing the majority of the shower activity, with
tops between 10,000-15,000 feet. MVFR conditions are likely with
any of this shower activity statewide through the evening, though
VFR will prevail.

Land breezes will take hold after sunset, allowing for clearing
over interior sections of the islands. Friday looks to be similar
to today with the sea and land breeze pattern continuing,
although an approaching upper level trough may fuel some heavier
showers by Friday night.

No AIRMETs are in effect or anticipated at this time.


A remnant frontal boundary lies near Maui while the west end of a
ridge of high pressure lies just southeast of the Big Island. The
overall wind flow is light with slightly stronger south and
southwest winds east of the boundary, mainly over the waters
around the Big Island. Sea breezes nearshore will transition to
land breezes overnight.

Winds will remain light Friday and Friday night, favoring a south
to southwest direction, as another weak front approaches the
area from the northwest. Low level winds will become more
westerly on Saturday as the front nears the state. Guidance
indicates a weak frontal boundary will move across the area
Saturday night and Sunday with north to northeast winds filling in
behind it. An area of high pressure will be passing by north of
the area Sunday night through Monday night with moderate trade
winds returning.

A small, short period northwest swell will continue to fill in
tonight, peak on Friday, then lower gradually Saturday and
Sunday. A series of very small, short period north swells will
move through the area Saturday through Tuesday. A larger northwest
swell is expected to arrive Tuesday night, peak Wednesday and
Wednesday night, then lower gradually on Thursday. Surf heights
may reach advisory levels during the peak of this swell. A series
of small south swells will be moving through the area through the
weekend and on through the middle of next week. Peak surf heights
will likely be on Saturday when the largest of these swells
arrive. Due to the lack of trade winds, surf will remain small
along east facing shores on into early next week. With the
expected uptick in trades around Tuesday and Wednesday, surf
heights are expected to gradually pick up at that time.






Previous Forecast Discussions may be found at
NWS Honolulu, HI (HFO) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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