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RH16 %
WindWSW 13 mph
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 242004

Area Forecast Discussion
National Weather Service Honolulu HI
1004 AM HST Fri Jan 24 2020

Light background winds ahead of an approaching cold front will
allow sea breezes to set up today. The front will stall and
dissipate near Kauai tonight as trade winds fill in. Winds will
shift southeasterly by Monday as a front passes by to the north
with land and sea breezes prevailing Tuesday into Thursday.
Another cold front may bring wet weather next weekend.


Visible satellite and radar show mostly sunny skies over most of
the state this morning with the exception of some low clouds and
showers anchored across windward and southeast slopes of the Big
Island. This area of clouds is associated with a pre-frontal
convergence band ahead of the approaching front just northwest of
Kauai. Zonal flow aloft will keeping the the atmosphere stable
through the next week. 12Z soundings show a strong inversion 7-8
kft high with perceptible water values from 0.78 inches at Lihue
to 1.16 inches at Hilo.

The approaching front is keeping the subtropical ridge over the
state resulting in light background flow, which will allow sea
breezes to set up this afternoon. Expect increasing cloud cover
with just a few light showers setting up across all island
interiors, but the relatively dry and stable atmosphere keep any
precipitation light. Cloud cover and showers will increase a bit
more this afternoon over Kauai as the front moves in and stalls,
but again, no significant rainfall is expected. Trade winds will
fill in over all islands tonight as a fast moving bubble high
behind the front pushes these winds ahead of the boundary. The
trades will focus clouds and light showers over windward areas by
Saturday, mainly for Kauai as the front dissipates.

The trade winds will taper off by and veer southeasterly Sunday
night and Monday as another cold front approaches from the
northwest. This front will not directly impact the islands as it
will pass well to the north on Monday. Yet another front will
follow this front and will keep the land and sea breeze pattern
flow going through much of next week. Expect clouds to build up
during the daytime and clear out at night, with no significant

Long range guidance shows the cold front moving into the western
islands next Friday, but there are differences between the GFS and
ECMWF. The GFS model brings the front into Kauai and Oahu on
Friday, while the European model keeps the entire frontal boundary
north of the island chain. Expect these differences in frontal
placement to diminish as the forecast time period grows shorter.


A dissipating cold front approaching the state from the northwest,
combined with surface high pressure over the islands, will again
allow for light and variable winds today with sea breezes developing
along most coasts. Expect dry and VFR conditions with most cloud
bases above 3000 feet, though a weak moisture push from the southeast
could bring a few showers to eastern portions of the Big Island. As
the front approaches this evening, weak tradewind flow and increasing
cloud cover are expected to return to Kauai and Oahu. No AIRMETS are
anticipated through this afternoon, but may be needed for mountain
obscuration on Kauai later tonight as clouds and showers increase
ahead of the front.


A front is currently on the verge of entering the Kauai coastal
waters and will bring a shift in winds this afternoon. North to
northeast winds are expected to begin increasing over the Kauai
waters over the next several hours and spread towards the rest of
the state late this afternoon into the evening. By tonight, winds
are expected to veer to the northeast and strengthen to moderate
to fresh speeds across the Hawaiian waters. Locally strong
easterly trade winds will then prevail through the weekend. A new
front will approach and stall out to the west of the islands early
next week, diminishing the winds over the western islands while
moderate to locally strong east-southeasterly winds hang on in
the unsheltered areas around Maui and the Big Island. Another
front approaching from the northwest during the middle and latter
part of next week, will diminish winds further, with light and
variable winds prevailing across most of the island chain.

Seas are expected to rise to SCA levels across a large chunk of
the marine area again tonight and Saturday as a new large
northwest swell arrives. Trade winds will also strengthen to SCA
levels across portions of the marine area this weekend. SCAs will
likely be required for most marine zones through the weekend due
to a combination of winds and seas, with some areas holding onto
SCA level winds and/or seas into early next week.

Surf will keep pumping along north and west facing shores as a
progressive weather pattern across the northern Pacific keeps a
series of large northwest swells moving through the islands. The
next northwest swell will fill in late tonight into Saturday with
surf peaking at warning levels on Saturday. This swell will be on
a downward trend Sunday, but may still hold at warning levels
during the day before dropping to advisory levels Sunday night. As
this swell eases early next week, advisory level surf may hold
through Monday before dropping below HSA threshold Monday night
and Tuesday. Over the Big Island, this swell will likely bring
advisory level surf to exposed west facing shores over the
weekend. Another large northwest swell will be possible during the
middle to latter part of next week.

Surf along exposed east facing shores will remain small through the
period due to the lack of persistent trades locally and upstream
across the eastern Pacific.

Surf along south facing shores will remain small through next week.
A couple background south swells expected over the weekend and
again on Tuesday should be enough to keep things from going flat.






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