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Temp-0.5 C
RH34 %
WindNNE 29 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

448
FXHW60 PHFO 260622
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
822 PM HST Sat May 25 2019

.SYNOPSIS...
A moderate and stable easterly trade wind flow will focus clouds
and showers across windward slopes through Sunday, with mainly
dry conditions prevailing over leeward areas. Trades will ease
slightly Memorial Day through Wednesday, leading to increased
chances for afternoon sea breezes and a few showers across
leeward areas. Trades are expected to strengthen Thursday into
next weekend, bringing a return of more typical trade wind weather
featuring windward and mauka showers and the occasional leeward
spillover.

&&

.DISCUSSION...
Currently at the surface, a 1027 mb high is centered around 1400
miles northeast of Honolulu, while a weak front remains nearly
stationary around 250 miles northwest of Kauai. The resulting
gradient is driving moderate trade winds across the state this
evening. The airmass remains rather dry and stable, with
precipitable water (PW) values between 1.1 and 1.3 inches, and
inversion heights between 5.5 and 7.5 kft. Infrared satellite
imagery shows a mix of low and high cloud across the island chain,
resulting in partly to mostly cloudy conditions. Radar imagery
shows a few showers moving into windward areas, with some
lingering daytime convective showers over leeward sections of
the Big Island. Main short term concern continues to revolve
around rain chances the next few days.

Model solutions are in good agreement showing high pressure
holding in place to the northeast of the state through the middle
of next week, while the stationary front lingers a couple hundred
miles northwest of the island chain. Moderate trade winds will
hold in place through Sunday, then ease slightly with boundary
layer winds shifting around to the east-southeast Memorial Day
through Wednesday. This will keep light to moderate east to east-
southeast winds in place across windward areas, while sea and land
breezes become common in many leeward areas. The stationary front
will dissipate by the middle of the week, with high pressure then
strengthening and shifting closer towards the state through the
end of the work week. This is expected to bring a return of trade
winds Wednesday night, with the trades then steadily strengthening
to moderate and locally breezy levels Friday into next weekend.

A fairly typical trade wind weather pattern will hold in place
through Sunday night, with showers favoring windward and mauka
areas and a stray shower reaching leeward communities from time to
time. The pattern will change slightly Memorial Day through
Wednesday, as sea breeze development in the more sheltered areas
will result in a few more showers developing each afternoon across
leeward and interior sections. There could be a few heavier
showers as well due to the increased moisture provided under the
east-southeasterly boundary layer flow. A transition back to more
typical trade wind weather is expected Wednesday night into next
weekend, with showers favoring windward and mauka areas.

&&

.AVIATION...
A high pressure center far northeast of the Hawaiian Islands will
produce a surface ridge north of the state. This surface ridge
will keep moderate easterly trade winds in the forecast for most
airfields over the next 24 hours. Wind speeds will likely remain
just below the threshold for moderate turbulence downstream from
mountain ranges.

A stable high pressure ridge aloft will keep lower trade wind
inversion heights around 7000 to 8000 feet, limiting shower
activity to the isolated to scattered range. Any showers that
develop will favor the windward and mountain areas. Mostly VFR
flight conditions are expected.

No AIRMETs are in effect and none are currently forecast.

&&

.MARINE...
A ridge just north of the area associated with a high far to the
northeast continues to bring in fresh to locally strong trade
winds. A Small Craft Advisory continues for the windier areas near
Maui County and the Big Island overnight. The ridge is expected to
weaken early next week, easing winds to light to moderate levels
Sunday, with lighter winds likely Monday into Wednesday. The
second half of the week should see the ridge building north of the
islands which will allow winds to return to fresh to strong
levels.

Surf along south facing shores is on the increase due to low
pressure systems in the southern hemisphere. Surf is expected to
approach advisory levels Sunday, but will continue to monitor buoy
reports overnight before making the final decision on the need for
a High Surf Advisory. This swell is expected to peak Sunday and
Monday, before declining Tuesday. A new long-period, although
slightly smaller, south swell is expected to arrive Tuesday and
hold into the middle of the week. Additional small south swells
are expected during the second half of the week.

A small northwest swell associated with a gale that crossed the
dateline a few days ago is expected to hold into Sunday before
slowly easing Monday through Tuesday. Another north-northwest
swell is possible Thursday. Surf along east facing shores will
remain up through the weekend due to the recent fresh to strong
trades upstream of the islands. Expect a downward trend early next
week as the trades weaken.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...M Ballard

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