154 
FXHW60 PHFO 202008
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1008 AM HST Fri Dec 20 2019

.SYNOPSIS...
Strong high pressure passing north of the islands will produce 
very windy conditions through Saturday, and possibly into Sunday.
An old front will also move through the state through early 
Saturday, bringing some wet weather to the islands. An area of low
pressure west of the state will cause mostly cloudy conditions 
across the area through the middle of next week. A wet weather 
pattern could develop around the Christmas holiday, but confidence
in the details remains low at this time. 

&&

.DISCUSSION...
A 1033 mb surface high is centered around 1200 miles north 
northwest of Kauai, while an old front is located around 50 miles
north of Kauai. Water vapor imagery shows an upper level low 
developing area of low pressure is located around 1200 miles west 
of the state. Infrarred and visible imagery shows a combination 
of low clouds and numerous showers moving onto Kauai from the old
front (ushered in by the trades) and convective debris cirrus 
streaming overhead along the eastern edge of the system west of 
the area. Partly cloudy skies persist across the eastern half of 
the state. 

The high will shift eastward well to the north of the islands 
during the next few days while the old frontal band pushes through
the island chain through Saturday. The upper low will lift northward
well to the west of the state. Winds are expected to really ramp 
up along and behind the old remnant front as it pushes through the
islands. Very windy conditions are expected to overspread the 
state tonight through Saturday and possibly linger into Sunday. As
a result, a Wind Advisory is now in effect through 6 PM this 
evening, and a High Wind Warning is in effect from 6 PM this 
evening through 6 PM Saturday.

More uncertainty in the wind forecast begins next week. The GFS 
drags a front into the island chain during the middle to latter 
part of the week, while the ECMWF keeps the front west of the
state. Given the continued uncertainty in the forecast, will 
follow a middle of the road solution which results in breezy to
windy trades through early next week, with winds shifting around 
to the southeast and easing during the middle and latter part of 
the week.

As for weather details, trade wind weather will continue through
early next week, with an increase in shower coverage and 
intensity as the old front passes by northwest to southeast today
through Saturday. Behind the frontal remnants, it appears that 
conditions will dry out a bit, with a decrease in shower coverage 
expected Saturday night. We should see the airmass gradually moisten
up by Sunday, with a more typical trade wind shower pattern then 
expected through the first half of next week. Much uncertainty 
continues in long range portion of the forecast, with the GFS 
indicating some heavy rainfall and thunderstorms could be in store
for the area Christmas Day through Thursday, while the ECMWF 
keeps the heaviest rain and thunderstorms west of the state.

A considerable amount of mid and high cloud cover is expected
today through much of next week. As a result, mostly cloudy 
conditions will be common statewide. Some thinning in the clouds 
can be expected at times, but timing the days with more sunshine
filtering through will be difficult to pin down until the models 
come into better agreement.


&&

.AVIATION...
A strengthening surface high to the north northwest of the state,
combined with a strengthening surface low west of the state, will
lead to breezy to windy east northeast trades today. Moderate 
turbulence is likely today along the leeward side of the mountains
with moderate to isolated severe turbulence expected late this 
evening and into tonight as very windy conditions develop. 

A dissipating front north of Hawaii will move southward today.
This feature will bring thicker cloud cover and more widespread 
precipitation to Kauai this afternoon, then Oahu this evening 
into tonight. MVFR conditions and mountain obscuration are likely 
as shower or squall activity moves through.

AIRMET Tango remains in effect for areas over and immediately
south thru west of mountains for all islands below 8000 feet due
to tempo moderate turbulence.  


&&

.MARINE...
Strong high pressure is building in north of the area. This will 
result in rather strong trade winds and rough seas resulting in 
rather hazardous boating conditions across most of the Hawaiian 
Coastal Waters. A Gale Warning is currently posted for waters 
north and west of Kauai and Oahu. This is expected to be expanded
to the remaining coastal waters by tonight. Winds are expected to
gradually diminish beginning Sunday. However, winds and seas will
likely remain elevated enough requiring a Small Craft Advisory 
for most areas on into early next week. 

The strong trade winds will produce rather large and rough surf 
along east facing shores through Sunday. Thus a High Surf Advisory
is currently in effect. With the expected drop off in trade winds
early next week, surf heights will gradually diminish as a result
but are still expected to remain rather elevated. There will be a
series of small north and northwest swells through the weekend 
and on into the middle of next week. Wave Watch III model guidance
indicates that none of these swells will be capable of producing 
advisory level surf. No other significant swells are expected. 


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 6 PM this evening to 6 PM HST Saturday 
for Niihau-Kauai-Oahu-Molokai-Lanai-Kahoolawe-Maui Windward West-
Maui Leeward West-Maui Central Valley-Windward Haleakala-Leeward 
Haleakala-Kona-South Big Island-Big Island North and East-Kohala-
Big Island Interior.

Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-Kona-
South Big Island-Big Island North and East-Kohala-Big Island 
Interior.

High Surf Advisory until 6 PM HST Sunday for Kauai Windward-Oahu 
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward 
Haleakala-South Big Island-Big Island North and East.

Wind Advisory until 6 PM HST Saturday for Haleakala Summit.

Gale Warning until 6 PM HST Saturday for Kauai Northwest Waters-
Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-Oahu 
Windward Waters.

Small Craft Advisory until 6 PM HST this evening for Oahu 
Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui 
County Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha 
Channel-Big Island Windward Waters-Big Island Leeward Waters-Big 
Island Southeast Waters.

Gale Warning from 6 PM this evening to 6 PM HST Saturday for 
Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-
Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward 
Waters-Big Island Southeast Waters.




&&

$$


DISCUSSION...Foster
AVIATION...Thomas
MARINE...Burke