High Surf in Hawaii, March 22 to 23, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
354 AM HST Fri Mar 22 2019

.SYNOPSIS...
A ridge of high pressure will continue to generate moderate to
locally strong trade winds through the early part of next week.
A lingering front north of Kauai will finally drift south and
provide a boost in trade showers Monday through Tuesday of next
week.

&&

.DISCUSSION...
Satellite imagery shows widely scattered clouds and showers,
moving rather quickly through the islands with the trades. The
showers are pretty much on the light side with rainfall totals
mostly under a tenth of an inch. Wettest spot is West Maui
Mountains with 4 tenths of an inch in the past 6 hours ending at
2 am HST. The morning soundings shows a strong inversion sloping
from 65 hundred feet over Lihue to 8k feet over Hilo. Models
suggest little change to this inversion through the weekend. No
real influx of low level moisture as well, with precipitable
water (PW) values under an inch to until Sunday/Sunday night where
it goes to slightly above an inch. With this said, we expect more
of the same tune as it has been for the past couple of days, that
is plenty of sunshine. Frequency of the showers should be picking
up as the evening progresses, becoming scattered to likely after
midnight. Once the sun rises, the frequency of these trade showers
should be trending down to isolated by mid or late morning. Light
rainfall amounts are anticipated under this stable air mass.

As for the winds, the strengthening trades has resulted in a Small
Craft Advisory for the windier near-shore marine zones, mainly for
waters around Maui County and south of the Big Island. See the
marine section for more details. The current surface high, 680
miles northwest of Kauai, will be reinforced by another high
tonight. The new high of 1030 mb, will then move east, passing
north of the islands on Sunday and Sunday night. This will
maintain the locally strong trades into Monday.

Changes in the weather are forth coming. The models are in good
agreement in finally dragging down the remnants of a boundary
between Monday and Tuesday morning. This boundary is currently 65
miles off Kauai's north shore. The GFS solution is indicating the
moisture with the boundary is capped at 10k feet, which is pretty
shallow, and is no higher than the Haleakala summit. The windward
and mountain areas will be the primary recipient to these remnants
when they move through, although some lee areas of the smaller
islands can expect more than isolated. At this time, the bulk of
the showers would have cleared the islands by noon Tuesday. It
looks dry for the rest of Tuesday, continuing through Wednesday,
while the trades become light. This will lead to a seabreeze and
convective regime on Wednesday. This change in the weather is due
to a front approaching the islands from the northwest.

&&

.AVIATION...
High pressure north of the state will keep moderate trade winds in
place through Friday, with clouds and showers favoring windward
slopes and coasts. Some MVFR cigs/vsbys will be possible in
showers across windward areas during the overnight and early
morning hours. Otherwise, predominantly VFR conditions are
expected through 12Z Saturday.

AIRMET Sierra is in effect for mountain obscuration across
windward sections of Molokai and Maui. Conditions should improve
here later this morning. Elsewhere, no AIRMETs are in effect.

&&

.MARINE...
High pressure north of the area will bring fresh to locally
strong trade winds today through early next week. A slight
decrease of trade winds is possible briefly early Saturday
morning, but winds will ramp back up to fresh to strong levels on
Saturday afternoon and hold through early next week. A Small Craft
Advisory (SCA) is now in effect for the typical windy waters
around Maui County and the Big Island at least through Sunday. In
addition, seas may reach border line SCA levels of 10 ft for
additional waters as a new north-northwest swell builds tonight.
Trades will ease towards the middle of next week as the surface
high weakens and is pushed to the southeast by an advancing front.
This front could reach the islands next Thursday.

Surf along north and west facing shores will be near advisory
levels today and will likely rise just above advisory thresholds
tonight, as a new north-northwest swell builds. The reinforcing
north-northwest swell is expected to peak late Friday in Saturday
and decline Saturday evening into Sunday. Several reinforcing
northwest and north swells should continue to produce small to
moderate surf for the first half of next week. By the middle of
next week, a moderate long-period northwest swell will be
possible.

As trade winds strengthen, rough surf along east facing shores
will gradually increase, with wind swell reaching around the March
average of 6 to 7 ft at 7 seconds late Saturday into Monday. Only
trace background southerly swell will occur.
&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

DISCUSSION...H Lau
AVIATION...Jelsema
MARINE...Kino