Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 250626
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
826 PM HST Thu May 24 2018

.SYNOPSIS...
Breezy trade winds are expected to persist through Friday night,
which will focus clouds and showers over windward areas. The lee
areas of the smaller islands can expect a few passing showers.
The trades are expected to ease somewhat over the weekend through
early next week. An uptick in trade showers may happen on Friday
night and Saturday, with additional showers on tap for Monday or
Tuesday of next week.

&&

.DISCUSSION...

A high pressure system is now 1000 miles NNE of Oahu this evening,
and continues on its eastward trek. By Friday evening, the high
will be 1200 miles NE of the islands, far away enough where the
breezy trade starts to weaken. We anticipate the rather widespread
moderate to strong trades to retreat to the typical windy areas
of Maui County and the Big Island by Saturday. A new high pressure
system will set up further north of the islands Monday, and move
to the east during the first half of the new week. This will
continue to keep trade winds on the lighter side.

An uptick in trade showers is expected Friday night and Saturday
morning as the remnants of an old front passes through the
islands. We anticipate a somewhat of a dry Saturday afternoon.

An upper level trough about 1000 miles west of Kauai this evening
is expected to move to the east through the weekend, stalling
west of Kauai during the first part of the new week. The ECMWF and
GFS are in good agreement with this upper level feature, but
differ on some of the effects on the islands. The proximity of
the upper trough, though, will be close enough to the islands to
destabilize the air mass, particularly the western islands, which
at the very least means some enhancements to the showers over the
islands during the first part of the week. We are awaiting the
latest ECMWF solution, to see how well it compares to the GFS.
The GFS shows the upper trough about 360 miles W of Kauai Monday
morning, with the 500 mb temperature at around minus 11 C over
Kauai. This is just enough to support a slight chance of a
thunderstorm for Kauai. It also safe to say we expect showers,
and rainfall totals to increase compared to what we have seen
over the last couple of days.

&&

.AVIATION...
Mainly VFR conditions are expected for all TAF sites through
Friday, though passing low clouds and showers may bring brief
MVFR ceiling and VIS conditions along the windward areas. There
may be enough low cloud coverage at times to warrant AIRMET MTN
OBSC along the windward slopes, but none is needed so far.

Brisk trade winds will persist across the area through Friday but
ease slightly as a strong high pressure far north-northeast of the
islands continues to advance east. AIRMET TANGO series remains
posted for low level turbulence over and immediately south and
west of mountains below 8000 feet on all islands. These conditions
are expected through Friday.

Periodic explosive eruptions at Kilauea/Halemaumau crater continue
to produce billows of volcanic ash at times, with the plume of
emissions predominately rising to slightly above the inversion
level and spreading to the southwest over Kau district on the Big
Island. MVFR VIS can be expected in this area and SIGMET TANGO
series for volcanic ash remains in effect.


&&

.MARINE...
High pressure north-northeast of the state will keep breezy trade
winds in place across the marine area through Friday night. The
trades will trend down over the Memorial Day weekend as an
approaching front shifts the high further eastward and away from
the islands. The trades will begin to strengthen on Tuesday as a
new high builds north of the state, with breezy conditions
returning for the middle and latter part of next week. A Small
Craft Advisory (SCA) remains in effect for all marine zones east
of the Kauai Channel with the exception of the windward Big Island
waters through 6 AM Friday. SCA conditions are expected to
continue for the typically windy waters around Maui and the Big
Island through Friday night, and this SCA may eventually need to
be extended through the day on Saturday.

Surf will remain below advisory levels along all shores through
at least the middle of next week. A series of south-southwest
swells will keeping surf along south facing shores near the
summertime average. Rough surf along east facing shores will
subside over the Memorial Day weekend as trade winds weaken

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay,
Pailolo and Alenuihaha channels, and waters south of the Big
Island.

Small Craft Advisory until 6 AM HST Friday for the windward and
leeward waters of Oahu and Maui County, and the Kaiwi Channel.

&&

$$


Lau/Hui/Jelsema


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