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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 152002

Area Forecast Discussion
National Weather Service Honolulu HI
1002 AM HST Sat Jun 15 2019

Trade winds will continue to flow through the islands well into
next week as a ridge of high pressure remains north of the
islands. An area of tropical moisture associated with a low level
trough will scrape the Big Island as it passes of the area this
afternoon and tonight. Otherwise, a drier than normal trade wind
pattern may hold through the early part of next week.


Fairly stable weather conditions persist across most of the main
Hawaiian Islands. The only exception is to windward Big Island
where there are some clouds and passing scattered showers. This
moisture belongs to a low level trough currently passing south of
the Big Island. It is still not so bad across windward Big Island.
The low level inversion may be buckling now, but it is still
pretty stable there. The low level moisture is contained below
11k feet. A somewhat drier regime should return early Sunday morning.

A stubborn surface trough, some 220 miles northwest of Kauai, is
finally moving on. This may have allowed a boost in the trades
overnight to locally strong. The passing disturbance south of the
islands may have some influence to strength of the trades too,
but the locally strong trades is here to stay well into next week.
The only caveat is the surface trough northwest of Kauai which
stalls some 700 miles northwest of Kauai on Monday. The trough
will be close enough to the main Hawaiian Islands to influence the
surface wind flow with a slight south component. The blocking
action of Maui and Big Island, will cause lighter winds to the
islands downwind of them. So, Kauai, Oahu, and Lanai, will
experience daytime sea breezes, which will lead to some spotty
afternoon clouds and showers across the interior and lee areas of
the Kauai, Oahu, Lanai, and Molokai. Locally strong trades, though
remains intact for the surrounding waters of Maui County and
waters south of the Big Island. Monday is the only blip in the
interruption of the trades. A more normal trade wind regimes
resumes the next day, Tuesday.

The forecast models (ECMWF and GFS), points to slightly cooler
mid level temps settling over the islands in the next 12 to 24
hours from east, in association of a mid level trough. In doing
so, it will push out the dome of warm temps now present over the
islands, which has kept most of the islands pretty much high and
dry. This cooler temps aloft may lead to slight rise to the trade
wind showers, especially the nights and mornings. Once this air
mass settles over the islands, it will be here for a while. In
essence, we will likely be trending to the more normal trade wind


Surface high pressure will remain to the northeast of Hawaii, while
a weak trough remains to the northwest. A weak trough will pass to
the south of the Big Island today, bringing enhanced showers to their
east and southeast sections. Otherwise, dry and stable air from an
upper-level ridge to the north of the state will keep moderate,
easterly trades in place with minimal shower activity focused
along the windward coasts and slopes through tonight. No AIRMETS
are expected through tonight, but will monitor the Big Island for
potential AIRMET Sierra for mountain obscuration if showers become
more widespread.


High pressure far northeast of the state will maintain fresh to
locally strong trades through around middle of next week. Winds
may veer east-southeasterly Monday into Tuesday as a weak trough
develops far west of the state. A Small Craft Advisory (SCA) is
in effect for the typically windy waters around the Big Island
and Maui through early Sunday morning. This will likely need to be
extended into the middle of next week.

Elevated surf is expected along south facing shores through the
weekend. The current south-southwest swell peaked early this
morning and will likely hold at advisory levels through the day
today. The south swell is expected to drop tonight into Sunday and
will likely drop below advisory levels by Sunday morning. Several
reinforcing south-southwest swells will continue to produce
average summer surf through middle of next week.

A northwest swell is expected late today into Sunday and will
continue to produce surf in the small to moderate range along
north facing shores through the weekend. Additional pulses of tiny
northwest swell are expected through next week. Surf along east
facing shores will remain small through the weekend, then rise
early next week.


High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai
Leeward-Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central
Valley-Leeward Haleakala-Kona-South Big Island-Big Island North
and East.

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



H Lau/TS/Kino

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