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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 200629
Area Forecast Discussion
National Weather Service Honolulu HI
829 PM HST Sun Jan 19 2020
Dry and pleasant conditions in place are expected to continue
this week. Breezy trade winds will hold through Monday, then
shift out of the southeast and diminish Tuesday through Friday. A
mostly dry land and sea breeze pattern will result, with the best
chance for a few clouds and showers setting up over interior areas
through the afternoon periods. A front will stall and weaken near
Kauai Friday with trades briefly returning Saturday.
A broad surface high is centered just north of Hawaii and will
provide stable conditions and breezy trades over the next day.
Dew points are in the low 60s across the state this evening, while
afternoon soundings at Hilo and Lihue showed strong, low inversions
and precipitable water between 0.75 and 1 inch. While conditions
are mostly dry, a small pocket of incoming clouds is observed on
infrared satellite just upstream of the smaller islands. This
pocket of moisture will bring a chance for a few light showers
over windward slopes through the night. Elsewhere, mostly dry and
pleasant conditions will prevail across the islands through Monday.
A progressive pattern setting up over the northern Pacific is
expected through the week as the jet becomes highly zonal. Two back-
to-back fronts passing to the north Tuesday and Friday will be
the result. The first front will shift the high towards the
southeast and bring the associated ridge over the islands. The
winds will respond by veering southeast and diminishing Tuesday
and continuing through Friday, allowing a land and sea breeze
regime to setup. Rain chances will remain limited due to the dry
air and strong subsidence expected through this time period. The
best chance for a few clouds and light showers will shift over
interior areas through the afternoon hours each day.
Long range GFS and ECMWF stall and weaken the front near Kauai on
Friday, with possible an uptick in showers for the northern end of
the state. Trade winds may briefly return Saturday as a bubble high
quickly passes north of the state before the next passing front
to the north causes the wind to veer out of the southeast Sunday.
This evening, the majority of the clouds and a few showers are
over the windward areas of Maui and the Big Island, as well as the
adjacent windward coastal waters. Expect windward areas of all
islands will likely see an uptick in shower activity during the
overnight hours before partial clearing by late morning Monday.
Brief periods of MVFR conditions are possible with these isolated
showers, but expect VFR to prevail overall.
Breezy trade winds warrant the continuation of AIRMET Tango for
tempo low level turbulence below 7,000 feet.
A surface high passing far N of the islands is supporting strong
NE trade winds, and a Small Craft Advisory (SCA) remains posted
for all waters through Monday. As the high moves steadily E and a
front approaches from the NW the next couple of days, winds will
veer and gradually weaken as the associated ridge moves closer to
the islands. Winds will become E Monday, light SE Tuesday, and
light and variable Wednesday and Thursday as the ridge moves over
the islands. A new high passing N of the islands around Friday
will push a second front toward the islands, while supporting
moderate trade winds heading into next weekend, with the front
currently expected to stall near Kauai and Oahu.
A new long-period NNW swell will build overnight, and surf is
expected to peak at advisory levels, thus a High Surf Advisory
has been issued for exposed N and W shores. This swell will
diminish late Monday and Tuesday, but will be followed on
Wednesday by a significantly larger NW swell that will likely
peak near High Surf Warning heights, with an even larger swell
potentially arriving next Saturday. Choppy surf along E facing
shores will gradually diminish as winds weaken the next couple of
days. Winds and seas warrant an extension of the existing SCA
through Monday, but diminishing winds and seas will allow its
cancellation by Tuesday at the latest. Seas associated with the
two large NW swells will warrant an SCA for most areas.
High Surf Advisory until 6 PM HST Monday for North and west
facing shores of Kauai, Oahu, Molokai and Niihau, and north
facing shores of Maui.
Small Craft Advisory until 6 PM HST Monday for all Hawaiian
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office