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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 120645

Area Forecast Discussion
National Weather Service Honolulu HI
845 PM HST Thu Aug 11 2022

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.



A steady weakening of trades will take place between now and early
next week due to the concurrent departure of the tropical low south
of Hawaii and weakening of the governing surface 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. High pressure over the northeast
Pacific will subsequently weaken and be forced southward causing the
local gradient to weaken and veer to easterly supporting an emerging
hybrid sea breeze pattern this weekend. As said height falls force a
decaying cold front southward toward the islands early next week,
the gradient will further weaken and veer to ESEly and will most
likely give rise to island scale land and sea breezes by Monday
or Tuesday.

CIMSS PWAT imagery reveals a much drier and more stable upstream
airmass crossing 150W and extending as far south as 15N at press
time. This airmass, formed beneath persistent mid-level ridging east
of the islands, will be ushered into the area 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.



Breezy easterly trades will continue through Friday, with clouds
and light showers favoring windward and mountain areas through the
overnight and early morning hours. Although VFR conditions will
prevail for most areas, MVFR CIGS and VSBYS will be possible in
and around passing showers.

AIRMET Tango remains in effect for low-level mechanical turbulence
leeward of mountains due to the gusty trades, but may be dropped
overnight into Friday as the trades slightly ease.



High pressure far northeast of the islands and a tropical
disturbance passing well southwest of the state is producing
fresh to strong trade winds across the marine area. 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-northwest and further away from the area,
while the high northeast of the islands weakens, we should see a
gradual decline in trade wind speeds through early next week.
Winds should be below SCA speeds in all zones over the weekend,
with gentle to moderate trade winds prevailing statewide early
next week.

Little in the way of surf is expected into next week. A small,
long-period south swell is expected over the next couple of days,
as well as a relatively short-period southeast swell, supporting
surf near or below seasonal averages along south facing shores.
Choppy surf along east facing shores will gradually diminish as
the trade winds ease during the next couple of days.

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




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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