Waianae, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

969
FXHW60 PHFO 211340
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
340 AM HST Thu Nov 21 2024

.SYNOPSIS...
Gradually diminishing trade winds will deliver just a few light
showers to windward areas of the smaller islands today, while
windward Big Island will continue to receive passing showers.
Light and variable winds and mostly dry weather are expected
statewide from tonight into Sunday. A weak front may move over the
islands from the northwest late this weekend. This front is
expected to bring little in the way of rainfall, however, and
winds will remain light through much of next week.

&&

.DISCUSSION...
Early this morning, weakening high pressure is located about 300
miles north of Honolulu, which is promoting light to moderate
trade winds over the islands. Dry air and stable conditions are
prevailing over most of the state, with the 12z Lihue sounding
showing stable conditions and a strong inversion near 5,000 feet.
CIMSS MIMIC Layer Precipitable Water (PW) imagery depicts values
between roughly 0.75 and 1 inch nudging over the smaller islands
from the east. Radar imagery also shows minimal shower activity
over much of the state early this morning, with the the exception
of windward Big Island where deeper mixing and lingering moisture
upstream continue to produce scattered to numerous showers.

Gradually diminishing trade winds will deliver little in the way of
rainfall to windward areas of the smaller islands today, while
windward Big Island will continue to receive passing showers.
Shower coverage and frequency over windward Big Island should
taper off by tonight, however, as background trade winds weaken
further and a land and sea breeze pattern develops statewide.
This will occur as the high pressure north of the state moves
south and dissipates, leaving a surface ridge near/over the
islands. Light winds and mostly dry conditions will persist into
at least Sunday, after which forecast details become a bit uncertain.

Late Sunday into Monday, a weak front is expected to approach
from the northwest, and deterministic model guidance continues to
offer inconsistent solutions for the prognosis of this feature
and the evolution of the weather pattern early next week. Ensemble
guidance, however, indicates that we can be confident that winds
remain light and precipitation totals associated with the
potential frontal passage will remain fairly low. A relatively dry
post-frontal weather pattern should persist well into next week
as we head into the Thanksgiving holiday.

&&

.AVIATION...
Trades will decrease gradually through Friday. Expect showery
weather for windward Big Island through today, with periods of
MVFR conditions. Some of the heavier showers may produce brief IFR
conditions. Elsewhere, expect fair trade wind weather with a few
light showers possible over windward and mauka areas.

AIRMET SIERRA is in effect for northeast through southeast slopes
of the Big Island due to mountain obscuration above 2500 feet.
This AIRMET will likely remain in effect through today as a
persistent band of showery low clouds extending east from the Big
Island continues to supply low clouds and showers to that island.
No other AIRMETS are in effect or are expected.

&&

.MARINE...
Weak surface high pressure will settle in over the far north
offshore waters today. This will create and maintain primarily
gentle to locally moderate trades winds through the rest of the
week. The west-to-east orientated ridge axis will reach the
northern coastal waters by Friday. This will result in continued
light to gentle east to variable breezes, with slightly stronger
winds in the Alenuihaha Channel and south of Big Island. Light
winds are favored ahead of the approach of a weak front nearing
Kauai on Sunday. This shallow frontal passage will disrupt trade
flow as early week gentle easterly breezes veer northwest then
northeast.

No significant swells are expected through early Friday as trade
wind waves continue to gradually subside and result in a more
calm sea state. Nearshore windward buoys are observing a 4 to 5
foot trade wind swell that will further decline throughout the
remainder of the week as a result of light trades.

A series of northwest and north-northeast swells are due within a
couple of days. A tiny 1 to 2 foot, 15 second period northwest
(320 degree) swell is being observed at the nearshore CDIP buoys
as it moves around the islands early this morning. This swell
will level out around 2 feet today and then hang in through
Friday. A larger 3 to 6 foot northwest (310-320 degree) medium
period swell developing from a pair of lows far northwest of the
islands is scheduled to travel through this weekend and peak
Sunday. A smaller reinforcing northwest pulse (320 degree) is due
Monday and Tuesday.

A small, short to medium period north (010-020 degree) swell will
slowly build in today and hold at 4 to 5 feet Friday and Saturday.
A very large, powerful storm force low churning off the U.S.
Pacific Northwest coast will send an overlapping north-northeast
(010-030 degree) swell across the islands late tonight or early
Friday, peaking Sunday into Monday and then fading Tuesday.

While none of these swells are expected to produce advisory level
surf, the potential for high surf along north and east-facing
shores will need to be monitored, especially as combining north
northeast swells peak Saturday through Monday.

&&

.FIRE WEATHER...
KBDI values remain high across the state and an overall dry
weather pattern is expected for the next several days. With this
dry air moving overhead, relative humidity values will have the
potential to reach the critical 45% threshold from late morning
through the afternoon each day through Sunday. Fortunately,
however, weak trade winds will mitigate fire weather concerns
through the rest of this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Vaughan
AVIATION...Powell
MARINE...Blood
FIRE WEATHER...Vaughan