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Temp3.9 C
RH56 %
WindNE 18 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

102
FXHW60 PHFO 030657
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
857 PM HST Tue Jun 2 2020

.SYNOPSIS...
Trade winds are expected to strengthen tonight and Wednesday,
then remain locally breezy through the weekend. Frequency of the
showers riding in with the trades will increase during the nights
and mornings, favoring the windward areas, although a showers will
drift downwind into the lee areas of the smaller islands. The
Kona side of the Big Island will cycle through morning sun,
followed by afternoon and evening clouds with isolated to
scattered showers each day.

&&

.DISCUSSION...
The strength of the trade winds is in the light to moderate range
this evening. Models are suggesting that it will be trending stronger
in the next 18 hours, reaching locally strong, and holding into
the upcoming weekend. There could be a delay to this onset as a low
level trough, noted by a low level swirl 800 miles east- northeast
of Maui, undercut the trades as it passing north of the islands
tomorrow. So, we will monitoring the winds closely. Otherwise, the
trades are being supported by a east to west oriented ridge of
high pressure located 750 miles north of Kauai. The ridge extends
to the parent high, stationed 1500 miles northeast of Kauai. this
high is forecast to edge closer to the islands during the second
half of the week, lending to the boost in the trades that will
persist into the upcoming weekend. With this boost in the trades,
it may bring on a slight uptick in trade showers.

Satellite infrared imagery shows a loose area of cumulus based
clouds with embedded showers, stretched out across the windward
waters of all the islands. There isn't much low clouds directly
east of the Big Island as well. With this said, the forecast
package was updated to lower the POPs for especially this
evening. The frequency of these showers should be increasing
in the coming hours to showers likely over the windward and
mountain areas of most islands. But we see about this as well.
It could be drier than predicted. Satellite imagery do show a
band of broken low clouds 150 miles northeast of Maui. Models have
the bulk of this band staying north of the islands, but clipping
Kauai starting at sunrise tomorrow and persisting through most of
Wednesday.

&&

.AVIATION...
Moderate trade winds will continue overnight into Wednesday, then
increase into the moderate to breezy category by Wednesday
afternoon. Clouds and showers will favor windward and mountain
areas each day, especially through the overnight and early morning
periods as pockets of moisture move through. MVFR CIGS and VSBYS
in and around these passing clouds and showers will be possible.
Although mostly dry conditions will prevail over leeward
locations, a few showers spilling over from windward areas can't
be ruled out.

No AIRMETs are currently in effect, though AIRMET Sierra may be
needed for some windward areas later tonight into early Wednesday
if cloud and shower coverage increase.

&&

.MARINE...
A High Surf Advisory (HSA) is posted for S facing shores of all
islands through Wednesday, as a significant long-period S swell
continues to build this evening. Overnight buoy trends will be
monitored to fine-tune the surf height forecast, and may also lead
to an extension in time of the HSA. Surf will likely remain below
advisory levels along all shores into early next week once the S
swell diminishes below advisory levels Thursday/Friday. However,
surf will not be flat as a smaller long-period S swell is expected
over the weekend, with another maybe early next week. A small
relatively short-period NW swell is also expected Wednesday and
Thursday. Minimal E shore surf is expected as trades deliver
short-period slop.

Trade winds are expected to trend stronger over the next day or
so, but confidence is somewhat diminished in this occurring during
the day Wednesday as a weak trade wind feature passes between the
islands and the trade-wind-supporting high centered far NE of the
area. A Small Craft Advisory (SCA) for the windier areas around
Maui and the Big Island does not appear to be verifying currently,
but with an uptick in wind speeds potentially occurring on Wednesday,
it will remain posted.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Wednesday for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai-
Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central Valley-
Windward Haleakala-Leeward Haleakala-Kona-South Big Island-Big
Island North and East.

Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


H Lau/Gibbs/Birchard

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