Small Craft Advisory 18, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
953 AM HST Fri Apr 27 2018

.SYNOPSIS...
A developing front will move down the island chain today through
Saturday, then stall near the Big Island Saturday night and Sunday.
Clouds and passing showers can be expected along and ahead of the
front as it moves across the area. A cooler and drier airmass
will fill in behind the front. Moisture associated with the front
may linger over The Big Island into early next week.

&&

.DISCUSSION...
Radar shows an area of showers moving up over Molokai, Lanai and
eastern Oahu. Also a few showers can be seen just west of Kauai.
The rest of the state is generally dry at the present time.
A rather strong area of low pressure both at the surface and
aloft can be seen spinning several hundred miles north of the
state. A cold front is developing from the low and extends south
to a position just west of Kauai. The front will move across Kauai
today accompanied by some light to moderate rainfall. The front
is forecast to reach Oahu later this afternoon and evening
accompanied by passing showers. The front will then move across
Maui County tonight and early Saturday then reach The Big Island
sometime on Saturday. Most of the showers will be light to
moderate in intensity but a few heavy showers are possible with
ahead and along with the frontal passage over Oahu and Maui
County. Thunderstorms are not expected as the best upper level
dynamics remain north of the state.

Behind the front, drier northerly flow will develop with a cooler
airmass filling in. However moisture associated with the front may
linger over The Big Island keeping things rather wet there into
early next week. Some snow is possible over the summits as well.

The low will remain north of the area into early next week.
Another weak front is forecast to move into Kauai Sunday night and
Monday with some light showers expected with its passage
especially along north facing slopes. This front is forecast to
weaken significantly and dissipate by the time it reaches Oahu.
Northerly flow will continue through Monday night with light trade
winds expected to return on Tuesday.

As we head into the second half of next week, a strong upper level
short wave trough is forecast to dig down northwest of the state.
Models indicate a wetter weather pattern setting up as moisture
gets drawn up from the south as well as moisture from the old
front moving in from the east. Details on timing, location and
rainfall intensities will need to be fine tuned as we get closer
to the event.

&&

.AVIATION...
Most of the instability seems to be focused on the middle islands
of Molokai and Lanai this morning. This is where we are observing
lower ceilings and the best chance for rain this morning. This
will continue into the afternoon and evening hours. AIRMET Sierra
is in effect for mountain obscurations for Molokai and Lanai. This
AIRMET may need to be extended to portions of Maui and possibly
Oahu later in the day if shower development is significant enough,
but with the lack of sunshine, this may not be necessary.

&&

.MARINE...
A developing low north of the islands will bring a front through
the island chain over the next couple of days. Heavier showers
will occur near Oahu and Maui County today through tonight. The
front is expected to stall near the Big Island Saturday night and
Sunday, with moisture lingering there during the first part of
next week. Northerly winds behind the front will approach SCA
criteria as winds accelerate around the terrain. The low will send
a mix of swells toward the islands this weekend into next week,
with associated seas rising above 10 feet in most zones late
Sunday and into Monday.

A moderate, long-period NNW swell will peak today with surf
heights remaining below advisory levels. The aforementioned low
developing north of the islands will remain in place until early
next week, but its evolution will dictate the amount of
swell/surf that arrives in the islands and remains somewhat
uncertain. Current indications are that a fairly significant, but
poorly organized, swell will produce advisory-level surf along
exposed north and west facing shores, with the peak of the swell
around Sunday.

Several pulses of small south swells are expected over the next
week or so, with a peak in swell energy Sunday. Rough and choppy
surf along east facing shores will diminish as the trades weaken.

See the latest Oahu Surf Discussion (SRDHFO) for additional details
on surf and swell.

&&

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

&&

Synopsis/Discussion...Burke
Aviation...Chevalier
Marine...TS