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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 141346

Area Forecast Discussion
National Weather Service Honolulu HI
346 AM HST Sat Dec 14 2019

High pressure passing north of the islands will keep breezy to
locally windy trades blowing today. The trades will ease some
later this weekend as the high moves away. Rainfall will favor
windward and mauka locales, with a few showers briefly reaching
leeward spots. The jet stream will bring increasing high clouds
today. A dry, stable airmass will take control of our weather
through the first half of next week, with few showers and
considerable sunshine. The next high passing far to the north will
return locally windy trades Monday and Tuesday.


High pressure passing to our north is driving locally windy
conditions to the islands this morning. This high will continue
moving to the east over the next couple of days, so trade winds
will trend down just a bit later this weekend. An upper trough to
the west of the islands has weakened, leading to fewer and less
intense trade showers. Upper level moisture riding in on the
subtropical jet will continue to bring high clouds at times, and
these will increase through today before pushing away tonight as
the jet shifts to the southeast of the islands.

Trade wind showers will decrease further early next week as stable
conditions and drier air move in. A strong upper high centered
just to our north will result in lots of sunshine and relatively
few showers. Rainfall will be light and should favor windward and
mauka sections during the nights and mornings. Showers will likely
increase again starting Thursday as mid-level heights fall near
the islands and cooler temperatures aloft start to make the
airmass a little more unstable again. The surface high to the
north will continue eastward through the weekend, so trade wind
speeds should decrease this evening into Sunday. The next surface
high will pass well north of the islands on Monday, returning
breezy to locally windy trade wind speeds for Monday and Tuesday.
The winds should ease Wednesday, but may increase again on
Thursday as the next in the series of highs passing to the north
approaches our longitude.


The island chain is experiencing periods of mountain obscuration
but nothing consistent as of now. Expect a moderate northeast
tradewind pattern with a majority of the rain showers affecting
the windward slopes. Winds may be strong enough in some areas to
push a few showers into leeward sections.

Winds will continue to be moderate. AIRMET Tango is currently in
effect for low level turbulence below 9,000ft. This AIRMET will
stay in effect through this forecast period.


The current large northwest swell will continue to subside, and
surf will lower to moderate levels today. A short period north-
northeast swell will keep surf elevated along exposed east facing
shores, mainly on Kauai and Oahu, through the day but should stay
below advisory levels.

A reinforcing large northwest swell is forecast to build late
Sunday into Monday and peak Monday night, possibly near warning
levels. This swell should slowly decline Tuesday into Wednesday,
but will likely be reinforced by another large northwest swell
Wednesday night into Thursday.

High pressure north of the state will keep moderate to breezy
trade winds over the area through today. With the trades remaining
relatively strong over the area, the Small Craft Advisory has been
extended for all zones until later this afternoon. Winds will then
begin to trend down slightly, likely resulting in small craft
winds being confined to the typically windier zones around Maui
County and the Big Island tonight. Seas will also lower as the
northwest swell subsides.

Trade winds should return to moderate to locally strong speeds by
late in the weekend and seas will build again with the reinforcing
northwest swell.


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

Small Craft Advisory until 6 PM HST this evening 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.




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
Send comments to: Ryan Lyman