Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 221949

Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Thu Mar 22 2018

Cloudy conditions with breezy trades will continue through Friday.
Showers will focus over windward areas with highest chances of
rainfall across the western portion of the state over the next
couple of days. An upper trough will approach from the west and
bring another wet period along with a few thunderstorms across the
state late Friday through Saturday night. Improving conditions
are expected Sunday into early next week.


Cloudy and breezy conditions continue across the state this
morning due to strong high pressure to the north and an upper
trough located far west of Kauai. Although most of the shower
coverage will continue to focus over the typical windward and
mountain locations today, heavier showers over Kauai and Niihau
are expected as a weak pulse of energy aloft moves through the
mid-level ridge. Radar shows a shield of moderate to heavy showers
moving in from the southwest over Niihau and Kauai. Expect this
trend to continue through today.

Models remain in decent agreement through Friday, supporting
breezy trades as strong high pressure far north of the area
shifts southeastward across the northeast Pacific. The upper
trough positioned to the west is forecast to begin shifting
eastward toward the region today. Highest rainfall chances will
remain over the western end of the state where the best source of
deeper moisture and upper support exists. Elsewhere, showers will
remain focused mostly over windward and mountain areas with a few
passing showers leeward periodically.

Models show a shortwave upper trough digging southeastward into
the area this weekend, bringing a threat for heavy rainfall and
even a few thunderstorms statewide. In spite of small
inconsistencies, GFS and ECMWF continue to depict low pressure
developing along an approaching trough in the vicinity of the
islands late Friday into Saturday, with an abundance of deep
moisture being drawn northward. This moisture, mixed with
increasing instability, will lead to a wet weekend and the
possibility of thunderstorms, especially late Friday through
Saturday. The highest probability for the heavy rainfall and
thunderstorms will be over the western end of the state late
Friday into Friday night before shifting eastward to Maui County
and the Big Island Saturday and Saturday night.

Improving conditions are expected Sunday through early next week
as drier air fills in and the upper trough and surface low lift
northeastward and away from the area. Models show light winds,
potentially giving way to overnight land breezes and afternoon sea
breezes by early next week.


The surface high to the north will slowly drift SSE into the
weekend, weakening the E winds. However, winds are still strong
enough to keep AIRMET TANGO for low-level turbulence to the lee
of the higher terrain through this morning.

Clouds and a few light showers continue to create MVFR conditions
over N and E sections of the Big Island Maui Molokai and Oahu
with more widespread rain showers around Kauai. AIRMET SIERRA
remains in effect for mountain obscuration for N through E
sections of all islands, but may be expanded later today to
include all of Oahu. In addition, AIRMET SIERRA for IFR conditions
is now in effect for all of Kauai. Light icing is also possible
around Kauai due to thick layered clouds.


The large NE swell has peaked, but is slow to diminish. According
to the buoy reports, warning level surf continues along the north
and east facing shores and a high surf warning remains in effect
until 6 pm HST this afternoon. Will likely require a high surf
advisory tonight and tomorrow as the swell slowly declines.

No other significant swells are expected through the rest of the
forecast period. The fading NE swell will be reinforced by a
small to medium pulse of 3 feet from the NNE between Saturday
night and Monday. This swell will be followed by a small to medium
NW swell between Sunday night and Tuesday. South-facing shores
can expect a slight rise in the surf on Friday when a small
southwesterly swell arrives.

The breezy trades will linger across our waters into Friday. The
Small Craft Advisory (SCA) has been extended to until 6 am HST
Friday morning. With the diminishing trades across our coastal
waters, and the dying NE swell, conditions will be generally
improving, however, there will still be a threat of inclement
weather over the weekend as an area of low pressure moves by to
the north. Westerly winds are expected to move in early next week
behind this area of low pressure.


High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Oahu North Shore-Oahu Koolau-Olomana-Molokai-Lanai
Makai-Maui Windward West-Maui Central Valley-Windward Haleakala-
Big Island North and East.

Small Craft Advisory until 6 AM HST Friday for all Hawaiian



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