High Surf in Hawaii, November 1 to 4, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
324 AM HST Mon Nov 1 2021

.SYNOPSIS...
Mostly dry and stable conditions with light and variable winds
will continue into Tuesday. The best chance for a few light
showers will be driven by sea breezes through the afternoon
periods. A return of a more typical trade wind pattern is
expected by Wednesday, which should continue through the weekend.

&&

.DISCUSSION...
Guidance remains persistent and depicts the weak ridge lingering
over the islands into Tuesday due to broad upper troughing over the
region and a couple of fronts passing to the north. The light
westerly background flow in the islands will continue through
tonight, then shift out of the north to northeast direction
Tuesday. This will allow the land and sea breeze regime to hold
with clearing conditions overnight through the mornings followed
by some cloud build ups that may produce a few light showers
through the afternoon hours over interior areas. The best shot for
these showers will remain over Kauai and Oahu where more moisture
resides near the tail-end of the passing fronts to the north.

A transition period is anticipated Tuesday through Wednesday as the
a ridge noses eastward trailing the front passing to the north. The
flow will shift out of the north-northeast later Tuesday, followed
by a return of moderate easterly trades Wednesday. Clouds and
showers will shift back over windward and mountain locations, with
the best chances being overnight through the early morning hours. A
residual band of moisture associated with the tail-end of the
aforementioned front may sag southward into the smaller islands
through the second half of next week, which could support better
shower coverage.

&&

.AVIATION...
Overall a dry and stable airmass, along with light winds,
remains over the region. Overnight some small bands of clouds
passed over the smaller islands at times, bringing brief MVFR
conditions, but otherwise mostly clear skies prevailed.

The overnight soundings from Lihue and Hilo both had precipitable
water (PW) values around 1.30 inches, however satellite derived
PW continues to show slightly drier conditions over Maui County
and the Big Island, which is in line with several models. As
such, still expecting a few more clouds and showers to be present
over Kauai and Oahu today.

The light winds are expected to once again produce afternoon sea
breezes that will lead to the development of clouds and isolated
showers over interior and leeward areas.VFR conditions are
expected to prevail however some isolated MVFR conditions possible
within some pockets of lower clouds or showers during the
afternoon and evening hours. Any showers that do form should
remain light.

Heading into tonight, Monday night, background winds near Kauai
are expected to become more northerly, with north to northeast
trade winds spreading back across the islands Tuesday.

There are currently no AIRMETs in effect and, at this time, no
AIRMETs are anticipated throughout the forecast period.

&&

.MARINE...
With a high pressure ridge near the islands, winds have been light
across the coastal waters. High pressure will begin strengthening
north of the state by Tuesday night into Wednesday, signaling
the return of trade winds. By Thursday, trades will become
moderate to breezy.

The first in a series of northwest to north swells over the next
week or so has been affecting local waters. A High Surf Advisory
(HSA) is in effect for most north- and west-facing shores from
Niihau to Maui. As this swell lowers later today; another,
larger, long-period swell will begin to move through beginning
tonight into Tuesday. The surf generated by this swell will likely
warrant a High Surf Warning (HSW) for most north- and west-facing
shores beginning early Tuesday, as surf is expected to reach at
least 25 feet along north-facing shores. The HSW will likely be in
effect into Wednesday before being replaced by an HSA. The swell
causing the higher surf will slowly subside through the end of the
work week. And early on, swell heights will likely reach at least
10 feet, so a Small Craft Advisory will be necessary for those
waters exposed to the incoming swell, beginning late Monday night
or early Tuesday morning.

Elsewhere, no significant swells are expected along east- and
south-facing shores through the new week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai
North-Molokai Windward-Molokai North-Molokai West-Maui Central
Valley North-Windward Haleakala.

&&

DISCUSSION...Gibbs
AVIATION...M Ballard
MARINE...Kinel