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Hawaiian Islands Synoptic Discussion and Guidance

637
FXHW60 PHFO 192006
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1006 AM HST Mon Oct 19 2020

.SYNOPSIS...
A stalled front near Kauai will focus clouds and passing showers
over the western portion of the state for the next couple of
days, with light to moderate south to southeast winds continuing.
Maui County and the Big Island will have fewer showers and light
east to southeast winds. The front will dissipate by Wednesday,
with light winds and mostly dry conditions prevailing statewide
from midweek through Friday. Another weak front may be near Kauai
over the weekend.

&&

.DISCUSSION...
A stalled frontal boundary lies near Kauai. Moisture associated
with the front is providing for passing showers over Kauai and
Oahu as well as over the adjacent coastal waters. Showers are
generally moving from south to north. Most showers are generally
on the light to moderate with a few embedded heavy showers seen on
radar. Daytime heating may allow for some increased shower
development over interior areas this afternoon and evening. Winds
are southerly over the west end of the island chain with light
east to southeast flow around the Big Island.

The frontal boundary will remain near Kauai over the next couple
of days and gradually dissipate over time. Showers will continue
to favor Kauai and possibly Oahu during this period with much less
in the way of shower activity over the rest of the the state. Winds
will continue to remain light across the area.

As the front dissipates Wednesday, the surface ridge will move just
N of Kauai, allowing light E-SE winds to form with a mostly dry
pattern expected for the remainder of the week. In this regime,
showers would be more favorable over windward areas during nights
and mornings, while afternoon sea breezes may bring clouds and a
few showers to interior and leeward areas. Dew points lowering
into the upper 60's should bring some relief to the recent mugginess,
but stronger, cooling trade winds are not anticipated.

As we head into the weekend, another weak frontal boundary may
move to a position near Kauai. Some increase in showers is likely
over and around Kauai if this was to occur. Winds will continue to
remain on the light side favoring an east southeast direction with
daytime sea breezes and nighttime land breezes occurring in
sheltered locations.

&&

.AVIATION...
A north to south front remains hung up around Kauai and Niihau
this morning, though the thick cirrus clouds from the past few
days have mostly thinned out. The front is forecast to dissipate
today through Tuesday. However, with some lingering upper-level
support, expect periods of showers to continue developing and
extend from Kauai County to as far east as Maui County this
afternoon. Cloud tops with these showers are mostly around
10-20kft, with some higher tops to 300kft possible in the
stronger ones.

The sharpening of a surface ridge over Maui County will lead to
a slight shift in surface winds today across the central islands.
The light southeast wind covering Oahu this morning will become
light to moderate south this afternoon. The winds across Maui
County will be mainly light southeast this morning, turning light
south and southeast this afternoon. Kauai will remain light to
moderate south, with the Big Island remaining light to moderate
east to southeast.

There is currently no AIRMET in effect, though one may be needed
for mountain obscuration this afternoon if shower activity
increases over Kauai and Oahu.

&&

.MARINE...
Light to moderate southerly winds and showery conditions will
continue over the Oahu and Kauai waters as a stalled frontal
boundary slowly diminishes through midweek. For Maui County and
the Big Island, drier conditions along with light to moderate
east to southeast winds will prevail with pockets of fresh breezes
possible in the channels and windier areas with this direction.
Although wind directions should shift back out of the east through
the second half of the week, wind speeds should remain light
enough for land and sea breeze conditions to continue near the
coasts as low pressure remains northwest of the islands.

Nuisance coastal flooding due to a combination of peak monthly tides
and water levels running near a foot above predicted will continue
through Tuesday. Impacts will occur around daybreak when the peak
daily tides occur through this time. See the latest Special Weather
Statement for more details regarding impacts. Daily tidal ranges
will lower through the second half of the week.

Surf along north and west facing shores will continue to lower into
Tuesday as the northwest swell that peaked over the weekend eases.
Outside of a small east-northeast swell that will impact exposed
north facing shores Tuesday through midweek, very little is
expected. Guidance shows a gale developing over the far northwest
Pacific near the western Aleutians Tuesday night into Wednesday,
then tracking eastward toward the Date Line through the second half
of the week. A large area of strong- to gale-force winds on the
backside of this feature focused at the islands within the 315 to
340 degree directional bands are shown with seas responding and
climbing to around 25 ft in this area. If this materializes,
expect a long-period, northwest swell locally to fill in Saturday
night into Sunday. More details will follow as the scenario
evolves.

Surf along east facing shores will trend up Tuesday through midweek
as an east-northeast swell arrives from a recent batch of strong
breezes that were focused at the islands near the west coast over
the weekend. Otherwise, small surf will continue due to the lack
of trades.

Surf along south facing shores will remain small through the week
with mainly a combination of background south-southwest and south-
southeast swell energy moving through.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Burke
AVIATION...TS
MARINE...Gibbs

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



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