Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/10/24

Area Forecast Discussion

National Weather Service Honolulu HI

 341 PM HST Sat Mar 9 2024

.SYNOPSIS...
Strong and gusty easterly trade winds will continue through the
weekend, as high clouds continue stream overhead. Rainfall will
favor windward and mauka locations, with a few showers
periodically carrying over leeward areas of the smaller islands.
As trade winds will decline Monday and Tuesday, a passing
disturbance aloft will clear the high clouds and may enhance
rainfall. Winds will likely be disrupted late Tuesday and
Wednesday, followed by a cold front advancing down the island
chain Wednesday night and Thursday. Breezy northerly winds and
drier conditions will follow the front.

&&

.DISCUSSION...
Strong and gusty trade winds will maintain a pattern of mainly
windward rainfall through the weekend, as high clouds continue to
stream overhead. The 1034 mb surface high driving the trade winds
will remain centered roughly 750 miles north-northwest of Kauai
tonight, then drift eastward Sunday. Meanwhile, a mid-level ridge
will produce stable conditions with an inversion based between
6,000 to 8,000 feet. Under this stable and strong trade wind flow,
wind prone areas of the Big Island and Maui County over and
downwind of terrain will continue to experience sustained winds up
to 30 mph with gusts around 50 mph, and a Wind Advisory is in
place through Sunday afternoon. Precipitable water within the
trade wind flow will run around seasonal normal through Sunday,
leading to typical rainfall along windward slopes, and the gusty
trades will periodically carry showers across leeward areas from
west Maui to Kauai. In the upper levels of the atmosphere, a sharp
trough centered just north of Kauai and extending to the
southwest is generating a thin shield of high clouds over most of
the state. As the upper trough sharpens and drifts eastward
tonight and Sunday, expect the high clouds to expand and possibly
thicken.

Trade winds will slowly decline on Monday and gradually veer more
easterly on Tuesday. The upper-level trough currently west of the
islands will pass overhead, leading to a decrease in high clouds
from west to east and increased chances for enhanced showers. The
GFS and ECMWF are not showing significant mid- to upper-level
cooling as the trough moves in on Monday, and though this does
not favor a substantial increase in rainfall, a briefly heavy
shower will be possible. As the 500 mb trough axis passes over the
Big Island on Tuesday, chances of locally heavy rainfall will be
highest across the eastern end of the island chain, and a
thunderstorm could flare over the Big Island interior with some
winter weather on the high summits.

Trade winds are expected to veer southeasterly Tuesday night and
become variable on Wednesday as a front approaches. Under this
scenario, east and southeast slopes of the Big Island should
continue to experience showers, as rainfall in most other areas
diminishes overnight and early Wednesday. On Wednesday afternoon,
expect sea breezes produce spotty showers, mainly over interior
sections of the islands.

While the exact timing is not yet clear, the front will move down
the island chain some time from late Wednesday through late
Thursday, bringing showers to mainly windward and northern
slopes. Behind the front, expect breezy northerly winds to usher
in a cool and rather dry air mass, with dew points possibly
falling into the low to mid 50s.

&&

.AVIATION...
High pressure north of the state will drive strong and gusty
trade winds through Sunday. Afternoon RAOBS and ACARS soundings
show 25-30 knots of wind below a strong inversion and visible
satellite imagery shows low-level wave clouds downstream of island
terrain. The current AIRMET TANGO for moderate low-level
turbulence downwind of the mountains is supported by recent
pilot reports and will likely continue through Sunday as similar
conditions remain in place. Moderate high-level turbulence may
redevelop tonight as the upper level trough sharpens and moves
eastward.

Showers embedded in the strong trade wind flow will bring periods
of MVFR conditions, particularly across windward sections, with
brief IFR conditions possible in heavier downpours. Otherwise, VFR
conditions will prevail at the TAF sites. An AIRMET for mountain
obscuration remains in place across windward Maui/Big Island, and
has been expanded back to windward Oahu due to greater shower
coverage/lower ceilings.

&&

.MARINE...
Strong high pressure north-northwest of the main Hawaiian Islands
will move east through Tuesday. This high will maintain a tight
pressure gradient across the island chain for the rest of the
weekend, keeping strong to gale force winds in the forecast
through Sunday. A Gale Warning remains in effect for the typically
windier channels and waters surrounding Maui County and the Big
Island through Sunday afternoon, and a Small Craft Advisory
remains in effect for all remaining coastal waters.

Early next week, winds will gradually begin to diminish but will
still remain fresh to near gale force in the windier channels
through Tuesday. Wind speeds will then continue to decline and
veer east-southeast by mid-week as the high moves further east
and a front approaches from the northwest. The front will move
across local waters from Wednesday through Thursday, followed by
moderate to fresh north-northeasterly winds filling in across the
region.

Surf along north and west facing shores is peaking this afternoon
and evening as a moderate size, medium period northwest (320-340
degree) swell moves through. Based on surf observations, latest
buoys, and model guidance, surf heights were again trended
slightly down from the previous forecast with this afternoon`s
updates. Otherwise, still expecting surf along north and west
facing shores to gradually decline tonight through Sunday as the
northwest swell fades. Surf along east facing shores will remain
rough and choppy through the rest of the weekend due to the strong
trade winds. A slight increase in surf along south facing shores
may occur on Sunday as a small, long period southwest swell moves
through. Regardless, south shore surf will remain tiny to small
throughout the next several days.

A pair of moderate, medium to long period north-northwest swells
are expected next week. The first, a northwest (320 degree) swell
originating from a compact hurricane-force low east of Japan, will
begin filling in Monday night and peak on Tuesday. After a brief
decline, a second north-northwest (330-360 degree) swell
originating from a broader area of gale force winds southwest of
the Aleutian Islands may arrive on Thursday and peak on Friday.
While the first swell origin`s source is a stronger low pressure
system, it is farther away and the swell size may be compromised
by angular spreading along its long eastern journey. The late week
swell`s fetch area will approach the islands more directly,
however, and is therefore expected to be the larger of the two.
This late week swell could produce advisory to warning-level surf
along exposed shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Sunday for Lanai Mauka-Kohala-Big
Island Interior-Lanai Leeward-Lanai South-Maui Central Valley
South-Kipahulu-South Haleakala-Big Island South-Big Island
Southeast.

Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters.

Gale Warning until 6 PM HST Sunday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

$$

DISCUSSION...Wroe
AVIATION...Bravender
MARINE...Vaughan