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Temp4.5 C
RH17 %
WindENE 14 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

076
FXHW60 PHFO 051413 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
413 AM HST Sat Dec 5 2020

.SYNOPSIS...
A cold front moving into the region from the northwest will
continue to weaken the high pressure ridge north of the islands
for the next few days. Trade winds will diminish as the front
approaches the islands with winds becoming more variable land and
sea breezes with a few interior showers each afternoon through
Sunday. Higher pressure will build back in north of the state with
moderate trade winds and passing showers forecast from Monday
afternoon through Tuesday. Light and variable winds return on
Wednesday and Thursday as yet another cold front moves into the
region.

&&

.DISCUSSION...
This mornings satellite imagery shows stable conditions over the
islands with scattered cloud cover in a light background
southeasterly wind regime. The band of clouds associated with the
old cold front has drifted northwest of the state. A cold front
roughly 900 miles northwest of Kauai will approach the state over
the next few days, decreasing wind speeds across the region.

The short range forecast guidance shows the islands on the edge
of the high pressure ridge axis through the weekend. Weaker large
scale pressure gradients under this ridge will weaken wind speeds
transitioning towards a light and variable wind pattern starting
later this afternoon through Sunday. A background large scale
light southeasterly flow will develop. In the absence of strong
large scale winds we expect local scale light and variable land
and sea breezes to form over the islands. Onshore sea breezes on
Sunday will lead to clouds building up over mountains and island
interior sections with a few showers in the afternoon to early
evening hours.

On Monday, the front stalls north of the islands and another
migratory high moves into the Central Pacific basin from the west.
High pressure building north of the islands will lead to a return
to moderate trade winds from Monday afternoon through Tuesday.

In the longer range forecast on Wednesday, light to moderate
southeasterly winds will develop across the region ahead of the
next approaching cold front northwest of the state. By Thursday
we see increasing trends in passing showers due to an upper level
trough moving across the state from west to east in a light to
moderate southeasterly weather pattern. Weather models are in
fair agreement with this changing weather pattern. The timing on
these wind and weather conditions may change a bit as the 5 to 7
day forecast period gets shorter.

&&

.AVIATION...
High pressure northeast of the state will weaken during the next
24 hours as a cold front approaches from the northwest. As a
result, the trades will diminish from east to west across the
state today. Sea breezes are expected to develop in many areas by
late this afternoon, with land breezes common statewide tonight.
Rather dry weather is expected across the island chain, with only
a few isolated showers affecting windward areas this morning, and
interior sections this afternoon.

AIRMET TANGO remains in effect for moderate low-level turbulence
over and downwind of terrain of all islands. Conditions should
improve by late this morning.

&&

.MARINE...
High pressure northeast of the state will maintain moderate to
locally fresh trades through the morning hours. As the East
Pacific high retreats a little further east in tandem with an
approaching northwest front, the pressure gradient back across the
chain should weaken later today and subtly weaken winds. The
Small Craft Advisory (SCA) has been extended through today but
scaled back to just include the Alenuihaha Channel and the waters
surrounding the Big island. Trades will gradually fall off through
early Monday, especially over the western end of the state in
response to the approaching boundary. An SCA for building seas may
be needed Sunday in association with an incoming larger, long
period northwest swell.

A quick-hitting moderate period northwest swell will come across
during the day that will lift western island north and west-facing
shoreline surf to near High Surf Advisory levels. A larger and longer
period northwest swell is anticipated to fill in early Sunday.
This swell is projected to drive surf heights along north and
west-facing shores to above High Surf Warning levels. This swell
will diminish from Monday on into the middle of the week. This
will allow surf to fall below Surf Advisory levels on Wednesday.

Relatively longer duration Surf Advisory to Warning-level surf
along with higher than predicted water levels will only
exacerbate ongoing coastal erosion issues. The best chance for
water to reach vulnerable coastal properties and roadways will be
around daybreak on Monday when the daily high tide could coincide
with the peak of this early week large northwest swell.

Surf along east-facing shores will remain small over the weekend,
then trend up slowly next week as the trades fill in locally and
upstream of the islands. Surf along south-facing shores will
remain small with a mix of small, short period southeast and
background south southwest energy moving up from the Southern
Hemisphere.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for Alenuihaha
Channel-Big Island Windward Waters-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...Jelsema
MARINE...Blood

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