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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 070138
Area Forecast Discussion
National Weather Service Honolulu HI
338 PM HST Fri Dec 6 2019
An upper trough will move east of the area tonight with a drier
weather pattern filling in. Winds will be light over the weekend
as high pressure moves off to a position far northeast of the
area. A weak front will stall near Kauai early next week and high
pressure will pass by far north of the area. Light to moderate
trades can be expected early next week. Another front will
approach the area around Thursday with winds becoming light once
again. Trade winds may return next Friday as high pressure builds
in to our north.
Water vapor imagery shows a shortwave trough over the eastern
half of the state. The airmass has become more stable over the
western end of the state on the backside of the trough axis as
indicated by the 00Z Lihue sounding. Some deep layered moisture
lingers over portions of the Big Island but most of the rain has
moved off to the east. Snow is tapering off over the Big Island
summits so the Winter Storm Warning has been cancelled. Also winds
have diminished over the summits so the Winds Advisory has been
cancelled as well.
The shortwave trough will be east of the area by Saturday morning
with a more stable and drier airmass moving in across the area.
Surface high pressure will be centered far northeast of the area
with a ridge extending southwest from the center to a position
just north of Kauai. This will cause winds to become lighter and
favor a southeast direction. The winds will be light enough to
allow for and and sea breeze circulations to set up. Showers will
tend to favor interior and mountain areas especially mainly during
the afternoon hours. The surface ridge will settle down over the
state on Sunday resulting in generally dry conditions and light
Sunday night and Monday, the tail end of a weakening front will
be near Kauai. An uptick in showers is expected especially over
Kauai. An area of high pressure will be passing by to our north.
This result in a return of light to locally moderate trade winds
early next week. Moisture embedded in the easterly flow will
primarily cause showers to fall over windward and mauka areas.
Winds will become light again Tuesday and Wednesday as the high
moves off to the northeast of the area.
Another front is forecast to approach the area on Thursday and
Friday with increasing shower activity expected, especially over
the west end of the state. High pressure building north of the
area will result in moderate trade winds.
An area of enhanced moisture that affected the state this morning
with widespread precipitation will continue to move east of the
Big Island this afternoon. In its wake, light to moderate easterly
trades exist. This flow will concentrate scattered showers along
windward coasts and slopes through this evening and into
tonight. Some MVFR conditions could exist, associated with these
showers, but not expecting anything widespread.
AIRMET ZULU remains in effect for areas east of Maui between
13000 feet and 26000 feet due to mod rime in precipitation.
High pressure far north of the islands will maintain moderate trade
winds into this evening, but expect a downward trend starting tonight.
Also expect the widespread showers and thunderstorm chances to end
tonight as the upper-level trough exits the area to the east.
Overlapping long-period swells from the north, and then the north-
northeast, will result in large surf for north and east facing shores
of most islands. The north swell will continue High Surf Advisory
(HSA) level surf for east facing shores today, but should remain
below the north shore advisory level until Saturday morning. As the
swell shifts around to the north-northeast tonight, swell and surf
heights will increase further, peaking Saturday through Saturday
night, with advisory level surf along north facing shores, and
possibly nearing warning levels for east facing shores. An HSA has
been issued for north facing shores, which goes into effect Saturday
morning. This swell will slowly decline through Sunday. Headed into
next week, advisory level surf is likely along north and west facing
shores with a couple of swells beginning Sunday night into Monday,
the latter of which could reach warning levels around mid-week.
High Surf Advisory until 6 PM HST Sunday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.
High Surf Advisory from 6 AM Saturday to 6 AM HST Sunday for
Oahu North Shore-Molokai Leeward-Maui Central Valley.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office