Current Conditions
Temp7.3 C
RH22 %
WindNE 17 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

432
FXHW60 PHFO 151304
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
304 AM HST Mon Jul 15 2019

.SYNOPSIS...
Breezy trade winds will continue each day through the week.
Clouds and showers will favor windward and mountain locations,
especially through the overnight and early morning periods. The
exception will be over the leeward sections of the Big Island,
where afternoon and evening scattered showers associated with the
sea breeze develop. Windward shower coverage may increase through
the second half of the week as moisture levels rise from east to
west.

&&

.DISCUSSION...
The latest analysis showed 1028 mb high pressure centered north
of the state and a decent pressure gradient over the region.
Breezy trades have resulted, especially in the windier locations
due to terrain accelerations. Observations at Kahului support this
where winds have been holding in the 20 to 25 mph range
overnight. In addition to the winds, shower coverage has been
minimal thus far through the overnight period due to the stable
and dry conditions. There were a few brief showers over windward
areas on Oahu with accumulations up to a tenth of an inch in the
past six hours (through 2 AM HST). Otherwise, dry conditions
prevail.

Guidance remains in decent agreement and shows the mostly dry and
stable trade wind conditions holding through the first half of the
week. Gusty trades will continue each day, especially through the
afternoon periods during peak heating/mixing. The best rainfall
chances will favor windward areas, leaving the leeward sections
dry. The exception will be over the leeward portions of the Big
Island, where afternoon and evening scattered showers associated
with the sea breeze will remain possible.

The extended guidance remains in decent agreement and supports
increasing moisture filling in across the eastern end of the state
by the end of the week as a weak trough approaches and passes to the
south. The ECMWF and GFS solutions depict PWs rising into the
1.5 to 1.75 inch range (above normal) Thursday through Friday. A
combination of the rising moisture, a weak upper low passing
through and trades will support increasing windward and mountain
shower coverage. Additionally, trades are forecast to strengthen
through this time as the gradient tightens between this passing
trough to the south and high pressure to the north. Some of the
windier locations may reach advisory criteria Wednesday through
Friday. Drier air will fill in Friday through the upcoming
weekend.

&&

.AVIATION...
High pressure north of the state will keep a moderate to locally
breezy trade wind flow in place through tonight. Relatively dry
conditions will prevail with a few light showers affecting mainly
windward and mauka areas. Brief MVFR cigs/vsbys will be possible
as showers move through, but predominantly VFR conditions are
expected statewide over the next 24 hours.

AIRMET Tango remains in effect for moderate low-level turbulence
over and downwind of the terrain of all islands. These conditions
are expected to hold in place through the day.

&&

.MARINE...
A 1028 mb high about 1000 nm north of Kauai will move east slowly
and strengthen. A trough far northeast of the area will move west
and dissipate. The pressure gradient south of the high will remain
tight enough to maintain locally strong easterly trade winds over
the Hawaii coastal waters through the week. A Small Craft Advisory
is in effect for the windy areas around the Big Island and Maui.
The advisory may need to be expanded around mid-week.

The large south swell affecting the Hawaii coastal waters is now
subsiding. The High Surf Warning has been downgraded to a High
Surf Advisory for all south facing shores through tonight. The
swell is aimed just southeast of the coastal waters so surf will
be highest on the Big Island and lowest on Kauai. This swell will
continue to slowly subside through mid-week. The locally strong
trade winds will produce choppy waves along east facing shores
but the fetch will be short for the next couple of days so wave
heights will remain small. Surf along east facing shores will
increase by mid-week as the fetch becomes longer. Only very small
surf is expected along north facing shores through the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Tuesday for south facing
shores.

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Jelsema
MARINE...Donaldson

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