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RH5 %
WindNE 27 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 200636

Area Forecast Discussion
National Weather Service Honolulu HI
836 PM HST Wed Feb 19 2020

Gusty easterly trade winds will continue through Thursday, then
gradually decrease Friday and Saturday as a front approaches from
the northwest. Although rainfall will focus over windward and
mauka locations, strong winds will push showers into leeward areas
at times as well. Winds will become light and variable by Sunday
as the front nears the islands, with sea and land breezes
expected statewide. Showers will favor interior and mountain
areas during the day and locations near the coast at night. Trade
winds are expected to return early next week, with rather wet
conditions possible over the western islands as the front stalls
out in this vicinity.


Currently at the surface, a 1034 mb high centered around 900 miles
north of Honolulu is driving strong and gusty trade winds across
the island chain this evening. Infrared satellite imagery shows a
large swath of low clouds over and upstream of the islands, with
cloud cover thickest in windward locales. Radar imagery shows
frequent showers pushing into windward areas, with coverage the
highest across Maui County and Oahu at the moment. Considerable
leeward spillover is also occurring due to the strength of the
trades. Main short term concerns revolve around trade wind trends
and rain chances through the remainder of the week and into the

Strong high pressure will slide eastward and weaken slightly over
the next few days as a cold front approaches from the northwest.
Strong and gusty trades will continue across the island chain
through Thursday, then trend lower Friday, before shifting around
to the east-southeast on Saturday as the front moves closer. Light
and variable winds will likely develop by late Saturday across the
western islands while moderate trades hold on across the eastern
end of the state. The gradient will slacken further Saturday
night, allowing a land breeze pattern to develop statewide, with
this sea/land breeze pattern holding in place through at least
Sunday night. Model solutions are in fairly good agreement showing
the front or its remnant band of moisture pushing into the
western islands Monday, then stalling out in this area through the
first half of next week before dissipating. As the front stalls, a
new high will slide by well to the north of the island chain.
Trade winds may begin to return on Monday, particularly across the
western islands, with the trades then taking hold Monday night and
continuing at moderate to breezy levels through the middle of next

As for weather details, despite precipitable water values around
1 inch, strong trades and the resultant orographic lift will be
very effective in wringing out a band of moisture as it passes
through the island chain overnight. Rather wet weather will be the
result, with windward areas seeing the showers most frequently
although quite a bit of leeward spillover can be expected, at
least across the smaller islands. A more typical trade wind shower
pattern should resume Thursday through Friday night, with showers
continuing to favor windward and mauka areas. A few showers will
continue to spread leeward, although there will likely be a
reduction in leeward shower coverage during this time.

Over the weekend, a transition over to a sea breeze/land breeze
pattern will keep showers favoring areas near the coast in an
east-southeast to southeast boundary layer flow at night, and
interior and mauka areas during the afternoon/early evening. A
transition over to a trade wind pattern will bring a return of
more windward/mauka showers and the occasional leeward spillover
early next week. Rather wet conditions could develop over the
western islands during the first half of next week however, as the
front or its remnants stall out in this vicinity.


Gusty easterly trades and showery conditions due to a band of
moisture/clouds in the area will continue into Thursday. Although
most of the shower coverage has been focusing over windward
sections of Maui County and Oahu, the tail-end of this cloud band
is beginning to move into windward areas of the Big Island this
evening. Some showers are spilling over into leeward areas of the
smaller islands, which will continue into Thursday with the strong
winds in place.

AIRMET Sierra for tempo mountain obscuration is in effect for
windward sides of Kauai, Oahu, Molokai, Maui and the Big Island.

AIRMET Tango remains in effect for tempo moderate low level
turbulence over and downwind of the terrain, as well as for strong
surface winds across the entire state.


A strong surface high pressure system is moving steadily east far
north of the area. The very tight pressure gradient south of this
feature is producing strong to near-gale force easterly trade
winds over Hawaiian waters, with winds reaching gale force in
areas where the wind accelerates around the islands. A Gale
Warning remains in effect through Thursday afternoon for the
typically windier waters adjacent to the islands of Maui County
and the Big Island. A Small Craft Advisory (SCA) also remains in
effect for all other Hawaiian Waters. The SCA will likely need to
be extended for most waters through Thursday night. After that,
it may be scaled back as winds and seas slowly diminish from
Friday through Friday night.

By this weekend, the surface high will move farther away to the
east, as a front approaches the state from the northwest. This
will allow the trade winds to weaken, and start to shift out of
the east-southeast over most areas by Saturday. The front is
expected to move into the far northwest Hawaiian offshore waters
Sunday, with strong northeast trade winds returning behind the

The strong trade winds will maintain surf above the High Surf
Advisory threshold of 8 feet along east facing shores through
Friday. This surf will subside over the weekend as the trade
winds weaken.

A new small northwest swell is expected to peak later tonight or
early Thursday morning, then gradually lower from Thursday night
through Friday. A slightly larger, long-period northwest swell
arriving late Friday will likely peak on Saturday, then gradually
lower from Sunday through Monday. A new large northwest swell is
possible early next week. Elsewhere, a series of small south and
south-southwest swells will maintain small background surf along
south facing shores through this weekend.


Wind Advisory until 6 AM HST Thursday for Kauai-Oahu.

High Surf Advisory until 6 PM HST Friday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 6 PM HST Thursday for Molokai-Lanai-
Kahoolawe-Maui Windward West-Maui Leeward West-Maui Central
Valley-Windward Haleakala-Leeward Haleakala-South Big Island-Big
Island North and East-Kohala.

Gale Warning until 6 PM HST Thursday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters.




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