Current Conditions
Temp-2.0 C
RH8 %
WindWSW 24 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

090
FXHW60 PHFO 041326
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
326 AM HST Thu Mar 4 2021

.SYNOPSIS...
Fairly typical trade wind weather will persist today, with
showers favoring windward and mauka areas. A surface trough will
develop in the vicinity of the islands tonight and Friday, then
slowly shift westward Friday night. This will bring wet trade wind
conditions particularly to windward sections of the smaller
islands. As the trough shifts westward over the weekend, a wet
trade wind pattern will continue as the trades rebound back to
breezy levels. The trades will strengthen further Monday through
the middle of next week, with windy and potentially very wet
conditions developing.

&&

.DISCUSSION...
Currently at the surface, a 1035 mb high is centered around 1300
miles northwest of Honolulu, and is driving moderate to locally
breezy trade winds across the island chain early this morning.
Infrared satellite imagery shows partly to mostly cloudy skies in
most windward areas, and clear to partly cloudy conditions in most
leeward locales. Radar imagery shows only a few showers moving
into windward areas of the smaller islands, with shower coverage
a bit greater over windward Big Island. Meanwhile, very little if
any shower activity is affecting leeward locales. Main short term
concern revolves rain chances during the next couple days.

High pressure northwest of the islands will weaken slightly as it
settles slowly southeastward during the next couple days.
Meanwhile, a weak surface trough will develop along the tail end
of an old front near or just north of the islands tonight and
Friday. This trough will keep the tightest gradient north of the
state, and maintain trade winds generally at moderate levels
through Friday. As the trough shifts westward Friday night and
Saturday, a new strong 1040 mb high will build north of the state.
This high will then slowly settle southeastward while maintaining
its strength of around 1040 mb through the middle of next week.
As a result, we should see winds increase over the weekend, with
windy conditions (possibly advisory level winds) in place late
Sunday through the middle of next week.

As for the remaining weather details, fairly dry trade wind
weather is expected today, although windward sections of Kauai
will likely see more shower coverage than the remainder of the
state. Quite a bit of high cloud cover will be overspreading the
islands as well due to an upper level trough digging to the
northwest of the island chain, but the degree of opacity appears
thin enough to allow for partly sunny conditions or filtered
sunshine.

Moisture will begin to pool along a weak surface trough developing
over or just north of the islands tonight and Friday, with this
trough then sliding slowly westward Friday night. This moisture
combined with added instability from a trough aloft, will lead to
an increase in shower coverage and intensity, particularly over
windward sections of the smaller islands. Considerable cloudiness
will prevail through the period due to a combination of high and
low clouds.

Once the surface trough shifts west of the state, we should see a
wet trade wind pattern take hold. Showers will favor windward and
mauka areas, particularly at night and during the early morning
hours, with a few showers spreading into leeward communities from
time to time. Models suggest that deeper moisture may arrive from
the east and southeast Monday through the middle of next week,
resulting in potentially very wet trade wind conditions across
the island chain. Additionally, moisture may extend high enough to
allow for a thunderstorm or two to develop over the Big Island
each afternoon Saturday through Wednesday. Will hold off on
mentioning thunder for now, as the most unstable conditions could
slide by just to the south of the state.

&&

.AVIATION...
The band of showers that passed over the state overnight has
diminished early this morning. Meanwhile, high clouds have begun
to stream across the northern islands from the west. High pressure
northwest of the state will allow for moderate northeast trade
winds to continue to flow over the main Hawaiian Islands today but
speeds are forecast to weaken a bit compared to the previous few
days. Isolated to scattered showers will ride in on the trade wind
flow today and impact mainly north through east sections of the
islands, though most showers should remain light with only brief
periods of MVFR ceilings/visibility. Models indicate that moisture
will increase as a weak surface trough approaches the islands
late this evening and overnight tonight. This will increase
chances for showers and MVFR cigs, especially for north through
east sections of the smaller islands.

AIRMET Tango remains in effect for tempo moderate turbulence
between FL220 and FL300 across the state as a jet aloft continues
to weaken early this morning. It is likely that this upper level
turbulence threat will diminish over the next couple of hours.
Additionally, AIRMET Tango also accounts for moderate low level
turbulence on the leeward side of mountains of all islands due to
the breezy easterly trade winds, but will also wane this morning.

&&

.MARINE...
The Small Craft Advisory (SCA) has been scaled back to include
only waters around Kauai, the Kauai Channel and windward Oahu
waters for hazardous combined seas near 10 feet. SCA conditions
may return for most waters Friday due to building seas, and extend
over the weekend as the high to our north is reinforced and
trades strengthen and become more widespread.

Surf heights remain below High Surf Advisory (HSA) thresholds
across all shores this morning. A bump in east shoreline surf will
occur late Friday night into the weekend as trade wind swell
increases and an arriving north swell wrap fills in. A northwest
swell will continue to fill today, peaking at or just below HSA
thresholds along north and west-facing shores late today into
Friday. A secondary, reinforcing north swell will arrive Friday
night and, in addition to the returning trade wind swell wrap, may
boost north facing shore surf heights to, or slightly above, HSA
heights Friday into Saturday and slowly diminish Sunday. A small,
long-period southwest swell will fill in tomorrow, providing a
small bump in south shore surf, and slowly decline through the
weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Friday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Vaughan/JVC
MARINE...Powell

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