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Hawaiian Islands Synoptic Discussion and Guidance

697
FXHW60 PHFO 280624
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
824 PM HST Wed Jan 27 2021

.SYNOPSIS...
High pressure north of the state will keep breezy trades in
place through Saturday, with a slight easing in the trade wind
speeds expected on Sunday. Showers will favor windward and mauka
areas with a few showers reaching leeward areas from time to time.
An old front will likely bring an increase in showers to the
islands on Friday however. The trades will diminish and shift
southerly early next week in advance of a cold front. The cold
front is expected to bring a more widespread rainfall event
Tuesday through Wednesday of next week, with cooler and breezy
conditions behind the front.

&&

.DISCUSSION...
Currently at the surface, a 1030 mb high is centered around 1050
miles north-northeast of Honolulu, and is driving breezy trades
across the island chain this evening. Infrared satellite imagery
shows partly to mostly cloudy conditions across the state, with
cloud cover most prevalent in windward areas. Meanwhile, radar
imagery shows scattered showers over windward slopes and coasts,
with a few showers making the trip over the mountains into leeward
locales from time to time. Main short term focus revolves around
trade wind trends and an increase in showers associated with old
frontal remnants moving through on Friday.

High pressure will build slowly southward and closer to the
islands tonight through Thursday night, before becoming absorbed
into a new re-enforcing high building southward far to the north
of the state Friday through the weekend. The gradient will remain
rather tight across the islands through the period. Breezy
conditions are expected through Saturday, before the trades
slowly ease to the moderate levels by Sunday. The trades are
forecast to diminish further Monday, then become disrupted and
shift southerly next Tuesday in advance of a cold front. Breezy
northerly winds are then expected following the cold frontal
passage Tuesday night and Wednesday, ushering in some cooler air.

As for the remaining details, typical trade wind weather is
expected tonight through the weekend. Showers will favor windward
and mauka areas and a few showers will reach leeward areas from
time to time. We expect an increase in shower coverage on Friday
however, particularly over windward areas, as both the GFS and
ECMWF show some old frontal remnants sliding southward through the
islands. This would likely send a few more showers into leeward
communities as well. Drier trade wind weather is expected for
Monday, with fewer windward and mauka showers. The lighter winds
will also allow for some leeward shower development in the
afternoon hours as a result of localized sea breeze development.
A cold front will likely bring more widespread rainfall to the
islands Tuesday through Wednesday of next week, with the potential
for some locally heavy rainfall and thunderstorms.

&&

.AVIATION...
Breezy trade winds will carry in clouds and showers into tonight
bringing tempo MVFR/isolated IFR conditions along windward slopes.
In the very near term, AIRMET Sierra for tempo mountain
obscuration is in effect for windward areas, but is expected to
expire on schedule at 07z/9pm HST. Fewer clouds and showers are
expected by Thursday.

AIRMET Tango remains in effect for low-level mechanical turbulence
leeward of all islands due to strong low level winds.

&&

.MARINE...
A strong high far north of the state will keep breezy to locally
strong easterly trade winds in place through Friday. A slight
decrease in trade winds into the moderate to breezy range will
develop by this weekend, as a weaker high passes by far north of
the island chain.

Large surf along east facing shores will continue through Friday
morning. The easterly trade wind swell will gradually decrease
from Friday afternoon through the weekend as the high pressure
system north of the area weakens. A Small Craft Advisory (SCA) for
all Hawaiian waters is in effect through early Friday morning. A
High Surf Advisory (HSA) for exposed east facing shores is in
effect through Thursday afternoon. This HSA may need to be
extended into Friday with continued strong trade winds.

The current small northwest swell will continue to hold through
Thursday with a slight reinforcing bump Thursday night. A new
moderate, long-period northwest swell will spread across the area
late Friday, and continue through Saturday night. Northwest swell
heights will slowly lower from Sunday into early next week.
Forerunners of a small, long-period north-northeast swell will
likely arrive Thursday and continue through the weekend.

The current small out-of-season southwest swell will slowly drop
tonight through Friday morning. Otherwise, expect small background
south swells Friday afternoon into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Thursday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

Small Craft Advisory until 6 AM HST Friday for all Hawaiian
waters-

&&

$$

DISCUSSION...Jelsema
AVIATION...JVC
MARINE...Kinel

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

Current Conditions
Temp		-4.3 C
RH		27 %
Wind		NE 34 mph
Road		Closed