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Hawaiian Islands Synoptic Discussion and Guidance

503
FXHW60 PHFO 121959
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
959 AM HST Fri Aug 12 2022

.SYNOPSIS...
Trades will steadily weaken and trend drier through the weekend
with limited rainfall focused over windward slopes. A land and sea
breeze pattern is likely early next week as background trades
become increasingly light.

&&

.DISCUSSION...
A steady weakening of trades will take place between now and early
next week due to the concurrent departure of the tropical disturbance
southwest of Hawaii and weakening of the subtropical high over
the northeast Pacific. The latter will occur in response to an
upper low in the Gulf of Alaska anchoring an expanding corridor of
height falls for the next several days. The high will
subsequently weaken and be forced southward as a result, which
will cause the pressure gradient to weaken and veer to east
southeasterly supporting a daytime sea breeze/nighttime land
breeze pattern by the beginning of next week.

CIMSS PWAT imagery reveals a much drier and more stable upstream
airmass crossing 150W and extending as far south as 15N at the
present time. This airmass, formed beneath persistent mid-level
ridging east of the islands, will be ushered into the area through
Monday by moderate trades as mid-level ridging builds aloft. The
result will be a steady increase in stability, an increasing dry
character to the trades, and warmer apparent temperatures as
trades trend lighter. Shallow pockets of moisture trapped beneath
the inversion will bring limited rainfall to windward slopes,
mainly at night, but otherwise the vast majority of locations will
stay quite dry.

A weak trough will pass just south of the Big Island on Tuesday
and may bring increasing showers to windward and southeast
portions of the island, as well as the leeward side Tuesday and
Wednesday afternoon. The rest of the state will continue the dry
and light wind regime into the middle of next week.

&&

.AVIATION...
Moderate to locally strong easterly trades will continue into
Saturday, with clouds and light showers favoring windward and
mountain areas. Although VFR conditions will prevail, brief
periods of MVFR CIGS/VIS are possible passing showers. No AIRMETS
are currently in effect and none are anticipated.

&&

.MARINE...
High pressure far northeast of the islands and a tropical
disturbance passing well southwest of the state, will maintain
moderate to strong trade winds across the marine area through
today. A Small Craft Advisory (SCA) remains in effect for the
windier zones around Maui and the Big Island through 6 AM
Saturday. As The disturbance moves steadily west or west-northwest
and further away from the area, and the high northeast of the
islands weakens, we should see a gradual decline in trade wind
speeds through early next week. Winds should ease below SCA
speeds in all zones over the weekend, with gentle to moderate
trade winds prevailing statewide early next week.

The combination of small, long-period south swells and short-
period southeast swells will keep south shore surf near to below
the seasonal average during the next 7 days. Choppy surf along
east facing shores will gradually diminish as the trade winds ease
during the next couple of days, with surf remaining below normal
through late next week. North shore surf will remain nearly flat
through the next 7 days.

&&

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


&&

$$


DISCUSSION...Foster
AVIATION...TS
MARINE...Almanza

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



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