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Hawaiian Islands Synoptic Discussion and Guidance

891
FXHW60 PHFO 091311
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
311 AM HST Tue Aug 9 2022

.SYNOPSIS...
The trades will strengthen today, with breezy to locally windy
conditions then expected through Thursday as a weak low or surface
trough slides by to the south of the state. The trades will ease
back to moderate and locally breezy levels Friday through early
next week. Fairly dry trade wind weather will prevail during the
next 7 days, with showers favoring windward and mauka areas mainly
at night and during the early morning hours. A stray shower may
reach leeward areas at times, but most areas should remain dry.

&&

.DISCUSSION...
Currently at the surface, a 1030 mb high is centered around 1800
miles north-northeast of Honolulu, while a broad trough of low
pressure is located around 700 miles south-southeast of the Big
Island. The resulting gradient is producing moderate to locally
breezy trade winds across the island chain early this morning.
Radar imagery shows scattered showers moving into windward
areas, with very little if any rain reaching leeward locales.
Main short term focus revolves around trade winds trends and rain
chances.

High pressure to the distant north-northeast will shift southward
and closer to the islands during the next few days, while a weak
area of low pressure, or surface trough, slides by around 300-400
miles south of the state. This should lead to a strengthening of
the trades today, with breezy to locally windy conditions
then continuing through Thursday, with a peak in trade wind
speeds on Wednesday. The trades should ease to moderate and
locally breezy levels Friday through early next week, as the high
northeast of the state weakens, and the low/trough shifts further
west and away from the island chain.

As for the remaining weather details, a fairly dry trade wind
pattern should prevail through the forecast period. Showers
will focus primarily over windward and mauka areas during the
overnight and early morning hours. A stray shower may occasionally
drift into leeward areas, although most areas will remain dry.
There remains the potential for an increase in showers over the
Big Island Wednesday night and Thursday as the weak low or surface
trough slides by to the south, but the latest trends suggest the
deepest moisture associated with this feature should remain to
the south of the state.

&&

.AVIATION...
High pressure far northeast of the islands will maintain breezy to
locally windy trade winds across the state. AIRMET Tango remains
in effect for low-level mechanical turbulence leeward of mountains
from Oahu to the Big Island. An upper level disturbance west of
Kauai and Niihau could bring some tempo moderate turbulence above
FL360 as it moves north, but conditions at the moment look to stay
below AIRMET criteria.

Satellite imagery continues to show an area of enhanced moisture
drifting west across the state. This has resulted in occasional
MVFR cigs along windward areas from Oahu to the Big Island. AIRMET
Sierra for tempo mountain obscuration will remain in effect for
these areas through at least the morning hours. Otherwise, expect
mainly VFR conditions at most locations as trades focus clouds
and showers along windward and mauka areas.

&&

.MARINE...
The typical pressure gradient caused by high pressure over the
northeast Pacific is being enhanced by a broad area of low
pressure well southeast of the islands. This is now driving
locally strong trades in the rest of the waters around Maui County
and leeward Oahu waters, in addition to the typical windier
locations around Maui and the Big Island. Therefore, the Small
Craft Advisory has been expanded to include those additional areas.
The SCA has also been extended in time for the typical windy
areas. A further expansion of the SCA may be required by late
tonight or early Wednesday, especially if wind speeds increase
further in response to any strengthening within this trough.

No significant swells are expected through the forecast period.
However, strengthening trades will build short-period wind waves
over east-facing shores through mid-week, peaking near or slightly
above the seasonal average Wednesday into Thursday. A very small,
long-period south swell arrives today, fading by Thursday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Thursday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters-Maui County
Leeward Waters-Big Island Windward Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Ahue
MARINE...TS

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



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