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Hawaiian Islands Synoptic Discussion and Guidance

519
FXHW60 PHFO 051625 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
625 AM HST Sun Jul 5 2020

.SYNOPSIS...
Light to moderate east southeast winds will continue through
tonight. Scattered showers will affect leeward and interior areas
at this afternoon as sea breezes develop, but clouds and showers will
favor windward areas otherwise. A more typical trade wind pattern
will resume on Monday with winds strengthening Tuesday and
maintaining through the end of the week.

&&

.DISCUSSION...
A 1031 mb high is centered around 1500 miles north of Honolulu
this morning driving light to moderate east southeast winds across
the state. The winds are lighter than usual due to a surface
trough between 500 and 800 miles north of Honolulu and a deep low
northwest of the state. An area of enhanced tropical moisture
moving in with the wind flow will continue to impact the island
chain through tonight. Radar and infrared satellite show low cloud
cover with scattered showers across Kauai and the Big Island,
particularly across the southeast sections of both islands, while
mostly dry conditions persist over Maui County and Oahu this
morning. Rainfall amounts overnight were generally light to
moderate.

The next area of clouds to the east and northeast of Hawaii will
move in later today and tonight. By afternoon, clouds and showers
are expected to build along island interiors and leeward sections
of most islands due to incoming sea breeze. Expect light to
moderate showers in these areas, shifting to windward areas
tonight, with the main area of clouds and showers finally passing
west of the island chain on Monday. Winds will maintain through
tonight, then begin to strengthen Monday as the trough weakens
and the high becomes the more dominant force. The incoming airmass
is expected to be a bit drier and more stable, however, clouds
and showers will focus over windward slopes as trades become
breezy by Tuesday through the end of the week. Showers will occur
mostly during the nighttime with the exception of the Kona slopes
on the Big Island (afternoon showers).

&&

.AVIATION...
A light easterly trade wind flow will persist through today as a
ridge of high pressure stays far north of the islands. The pool of
warm and unstable air continues on its way out. In doing so, heavy
showers moved into Kauai shortly before midnight. These showers
are currently dissipating over interior Kauai. Showery weather is
still happening over the Hilo and Puna districts of the Big Island
this early Sunday morning. Scattered showers are also detected
moving down the adjacent Kau coastal waters, briefly touching the
shoreline at times. There is no AIRMET Sierra for this area, but
will be monitored closely. As part of a drier and more stable air
mass spreading in, these showers affecting windward Big Island are
expected become isolated by mid morning.

Lingering moisture and instability, coupled with local sea breeze
and daytime heating, will lead to some isolated, spotty, showers
over the lee and interior sections of the remaining islands this
afternoon. Scattered showers are on tap for leeward Big Island
this afternoon. Also, the trade winds, although weak, will be
able to bring in a few showers onto the windward areas of all the
islands. So do expect brief MVFR ceilings and vis with these
showers. The amount of showers is expected to be less compared to
Saturday. A more regular trade wind pattern should be in place by
this evening.

&&

.MARINE...
Light to moderate east-southeast winds will hold today as a weak
trough west of Kauai continues westward and away from the state.
Winds will remain light enough for afternoon sea breezes to
develop for some leeward coastal areas today. 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 remain small with mainly a
mix of small south and south-southeast energy holding. Guidance
does introduce a small background south-southwest swell arriving
today, 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 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
today. This 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

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Wind		NE 18 mph
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