Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 221309

Area Forecast Discussion
National Weather Service Honolulu HI
309 AM HST Thu Feb 22 2024

Moderate to locally breezy east to east-southeast trades will
prevail during the next couple days. Rainfall chances will remain
highest over windward and mauka locations, particularly during
the overnight and early morning hours, with afternoon showers
possible over leeward areas each day. Increasing moisture and a
return of breezy easterly trades will support greater windward
shower coverage over the weekend through the middle of next week.


Currently at the surface, a 1034 mb high is centered around 1250
miles north of Honolulu, while a 1002 mb low is positioned around
1050 miles west-northwest of Kauai. Moderate easterly trade winds
prevail in unsheltered sections of the island chain early this
morning. Infrared satellite imagery shows mostly cloudy
conditions across much of the state. Radar imagery shows scattered
to numerous showers moving into windward slopes and coasts, with
quite a few decaying showers spilling into leeward communities.
Main short term focus revolves around trade wind trends and rain
chances during the next few days.

High pressure will strengthen as it remains nearly anchored well
north of the islands today through Friday, while a low west-
northwest of the state shifts northeastward to a location between
800 and 1000 miles northwest of Kauai. A slight strengthening of
the trade winds is expected during this time, although they will
generally hold at moderate to locally breezy levels. Due to the
east-southeast boundary layer flow, some localized leeward sea
breezes will be possible in the more sheltered leeward areas each
afternoon as well. The low will weaken and eventually dampen into
a trough over the weekend, while the strong high to the distant
north settles southward and closer to the island chain. This will
ramp the trades up to breezy levels statewide and shift the
direction around to a more typical east-northeasterly direction.
The strong high will hold north of the state early next week,
before being reinforced by a new strong high to the distant north
around the middle of next week. Breezy trades are expected to
continue early next week, with windy conditions possible at times.

As for the remaining weather details, little change in the
overall weather pattern is expected through Friday. Showers will
favor windward slopes and coasts. Decaying showers will reach
leeward communities at times, and a few leeward showers also
developing each afternoon with the assistance of localized sea

There remains some uncertainty on how far east a front will make
it late in the week, with the GFS remaining less progressive and
further west than the ECMWF. This difference is impacting timing
details on a shallow moisture boundary associated with an old
front moving through the state Friday night and Saturday. Given
the timing uncertainty, we will continue to advertise a typical
trade wind weather pattern, with the expectation that a 6-12 hour
period could be rather wet when this boundary moves through.
Beyond that, fairly typical trade wind weather can be expected
Saturday night through the middle of next week, with showers
favoring windward and mauka areas and a few showers spilling
leeward from time to time.


Moderate trades will continue, with clouds and light showers
favoring windward and mauka locations. MVFR CIGs/VSBYs will
persist this morning for some windward areas, mainly in showers.
Some of these showers are managing to spread into leeward sections
of the smaller islands.

AIRMET Sierra is now in effect for mountain obscuration over
north through southeast facing slopes of Kauai, and will likely
continue through the morning hours today. Other windward locations
may need to be included later this morning.


Fresh easterly trades develop tonight into Friday as high
pressure builds over the islands in tandem with deepening low
pressure northwest of the area. The Small Craft Advisory remains
posted for the typical windier waters and will likely require
expansion as winds continue strengthening into the weekend. Fresh
trades continue well into next week.

The current moderate, long period NW swell peaked yesterday
evening into last night and will now steadily subside through the
remainder of the week. Another moderate, long period NW (330)
swell is modeled to arrive early this weekend bringing similar
surf to exposed shorelines. Surf may approach the advisory
threshold during its peak late Saturday into Saturday night.

East-facing shores remain dominated by short period wind wave
through the near term. However, deep low pressure descending from
the Gulf of Alaska down the West Coast of the mainland US will
generate a moderate, medium period NNE (060) swell that will fill
in late this weekend and peak early next week.


Small Craft Advisory until 6 PM HST Friday for Maui County
Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.



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