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Hawaiian Islands Synoptic Discussion and Guidance

986
FXHW60 PHFO 050646
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
846 PM HST Sat Jul 4 2020

.SYNOPSIS...
Light to moderate east-southeasterly trades will continue through
Sunday. Showers will favor windward and mauka areas, although
scattered showers will also affect leeward and interior areas at
Sunday afternoon. A more typical trade wind pattern will resume
on Monday, with showers favoring windward and mauka areas along
with the stray leeward spillover. This trade wind pattern will
hold through late next week, with breezy conditions expected
Tuesday into next weekend.

&&

.DISCUSSION...
Currently at the surface, a 1031 mb high is centered around 1600
miles north of Honolulu, while a weak trough of low pressure is
located several hundred miles northeast of the state. The
resulting gradient is producing light to moderate east-southeasterly
trades across the island chain this evening. An area of enhanced
tropical moisture moving in with the wind flow will continue to
impact the island chain through Sunday night before drier air
moves in. Radar and infrared satellite show scattered clouds and
showers across Kauai, Oahu and the Big Island with mostly dry
conditions over Maui County.

The gradient will remain disrupted from the high far north of the
islands through Sunday night as trough moves westward and dampens
out, allowing the high to become the more dominant feature. The wind
speed will maintain though Sunday night with localized sea and
land breezes developing in the more sheltered leeward areas.
Expect showers to focus over windward areas through tonight and
Sunday morning, shifting to leeward interior areas Sunday
afternoon and evening. Some showers will be of moderate
intensity. Trade winds will strengthen Monday ushering in drier
air and more stable weather. Winds will strengthen further on
Tuesday and maintain through late in the week.


&&

.AVIATION...
A light easterly trade wind flow will persist through Sunday,
as a ridge of high pressure stays far north of the islands. A
passing low level trough brought a pool of warm and unstable air
on to the islands last night and today. Now, we anticipate the
islands to be drying out the rest of tonight through Sunday. Any
ongoing showers now over leeward areas of the smaller islands will
be ending shortly, as a land breeze takes over. The background
easterly trades will, however, continue to carry a few showers in,
favoring the windward and mountain areas. Expect some brief MVFR
ceilings and vis with these showers, which we expect to be less
than earlier today. Windward Big Island, which has improved in
the past couple of hours, may get another round of scattered
showers after midnight, and potential AIRMET Sierra for mountain
obscuration. This weather is in association with an area of low
level moisture embedded in the trade flow, and should clear up by
mid morning Sunday. With light trades on tap for Sunday, local sea
breeze, combined with ample leftover moisture and instability will
result in some spotty afternoon showers over the interior and lee
areas of the smaller islands once more, although not as pronounced
as today over some islands. Scattered showers is on the menu for
the lee and interior sections of the Big Island Sunday afternoon.
AIRMET Sierra is still in place for the mountains of Oahu and the
Big Island, but will likely be taken down by 1000z as these
showers gradually clears out.


&&

.MARINE...
Light to moderate east-southeast winds will hold into Sunday as a
weak trough near Kauai continues westward and away from the state.
Winds will likely remain light enough to allow overnight land
breezes and afternoon sea breezes for some leeward areas through
Sunday. A return of a more typical trade wind pattern is anticipated
Monday with winds hitting the moderate to fresh range, then the
fresh to strong category by Tuesday. As a result, a Small Craft
Advisory for winds will be possible as early as Tuesday for the
typical windier waters from Maui County to the Big Island. For the
extended, the advisory may need to be expanded to other marine areas
as the trades continue to ramp up. Seas will approach, if not reach,
the advisory level (10 ft) over the Alenuihaha Channel and waters
south of the Big Island by the end of the week.

Surf along south facing shores will continue to trend down into
Sunday with mainly a mix of small south and south-southeast energy
holding. Guidance does introduce a small background south-southwest
swell arriving tonight into Sunday, which will support the small
surf continuing into Monday. Another south-southwest pulse will be
possible Wednesday through the second half of the upcoming week. For
the extended, guidance depicts a a solid area gales setting up in
the Tasman Sea through the first half of the upcoming week, which
could result in an uptick in surf locally by mid July.

Surf along east facing shores will remain small through Tuesday,
then gradually trend up through the rest of the week as the trades
increase locally and upstream of the islands across the eastern
Pacific.

Surf along north facing shores will remain near the summertime
average through the upcoming week. A background, medium period,
northwest swell may be enough for small surf at select spots Sunday.
If it arrives, it will be short-lived and out by Monday. Some spots
exposed to trade wind wrap may notch up through the second half of
the upcoming week.


&&

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

&&

$$


DISCUSSION...Foster
AVIATION...H Lau
MARINE...Gibbs

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