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RH100 %
WindNE 26 mph
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Hawaiian Islands Synoptic Discussion and Guidance

797
FXHW60 PHFO 240141
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
341 PM HST Wed Sep 23 2020

.SYNOPSIS...
Trade winds can be expected for the next few days as high
pressure passes by far to our north. An area of enhanced moisture
will provide for a period of passing showers through tonight
primarily for windward and mauka areas. Winds will be lighter over
the weekend and on into early next week as a frontal system moves
closer to the area from the northwest. The airmass will be fairly
dry and stable so just a few showers are expected.

&&

.DISCUSSION...
Surface high pressure centered far to the north northwest of the
area is providing for moderate trade winds across the state. An
area of enhanced moisture is seen on satellite imagery moving into
Maui County and the Big Island. Radar shows numerous showers fall
over eastern and interior sections of the Big Island as well as
over the windward slopes on Molokai and Maui. A few light passing
showers are seen elsewhere primarily over windward slopes and
summits. The area of moisture is expected to spread up over Oahu
and Kauai this evening and overnight. Shower activity is expected
to increase especially over windward and mauka areas with the
trade winds sufficiently strong enough to blow over showers over
to select leeward areas at times.

The surface high will move slowly eastward over the next few days
with an uptick in trade winds expected. Passing light showers will
continue to favor windward and mauka areas with most leeward
locations remaining dry.

As we head into the weekend, the high will have moved to a
position far to the northeast of the state while a frontal
boundary far to the northwest nudges the highs associated ridge
axis a bit south. This will cause the trade winds to become light
to moderate allowing daytime sea breezes and nighttime land breezes
to become widespread. The sea breezes will produce afternoon clouds
and spotty showers, but a ridge aloft will keep the atmosphere stable,
so rainfall will be light.

By early next week, the front will be located a few hundred miles
to the north northwest of the state. Winds will become rather
light with land and sea breezes dominating. The airmass will
remain rather dry and stable so shower activity will be rather
limited.

&&

.AVIATION...
With high pressure entrenched north of the islands, trade winds
will be moderate to locally breezy through Thursday.

An area of showers, and accompanying MVFR conditions, is moving
from the east and will mainly affect windward and mauka sections
across the state, with the Big Island, Maui, and Molokai still
seeing the most activity this afternoon. Otherwise, VFR will
prevail.

An AIRMET for mountain obscuration is currently in effect for
windward parts of the Big Island, Maui, and Molokai.

&&

.MARINE...
A secondary area of high pressure building in behind an eastern
Pacific cold front will maintain this ongoing north-south pressure
gradient across the state. This will result in moderate to fresh
trades with a slight strengthening through late Thursday. These
anticipated higher trades will occasionally become locally strong
within the channels surrounding Maui County, Maalaea Bay and those
waters south of the Big Island. Thus, a Small Craft Advisory
(SCA) remains in effect for these waters through at least Friday
morning. Expect winds to weaken below SCA criteria Friday with
weakening winds to a light breeze Sunday.

Buoy 51001 began reporting the passage of high period forerunner
northerly swells early this afternoon. While the bulk of this
earlier week Gulf of Alaska energy will ride east of the islands,
the state will still get clipped by this energy. There will be a
significant jump in surf along all north-facing shores over the
next 36 to 48 hours. Wave heights will peak out tomorrow while
staying below advisory levels with a gradually downtrend Friday
and Saturday. A nice bump in the long period southwest swell
moving up from a generation area south of New Zealand a couple of
days ago should pick southern-facing shore surf up another foot or
so through Thursday. Another day or three of moderate to fresh
trades will result in the maintenance of seasonal east-facing surf
into the weekend. After a weekend of weaker trades and lowering
surf, eastern swell front runners may arrive from (what will be
left of) Tropical Cyclone Lowell's East Pacific easterly fetch.

&&

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

&&

$$

DISCUSSION...Burke
AVIATION...Kinel
MARINE...Blood

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office