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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 250651
Area Forecast Discussion
National Weather Service Honolulu HI
850 PM HST Sun May 24 2020
Lighter winds and mostly dry weather are expected through Tuesday,
with a few showers possible, mainly during the afternoon and
evenings. Trade winds are expected to strengthen Wednesday, and
remain in place into next weekend, delivering a few brief showers to
Currently, light to moderate E-SE winds prevail on the large scale,
lighter near Kauai as compared to the Big Island, due to a surface
ridge located a couple hundred miles N of Kauai. The low-level flow
is mostly dry, except upstream of the Big Island, where a few
showers are riding in on the trades, although high clouds are
somewhat hiding them from being seen in latest infrared satellite
images. The island atmosphere is stable, with a nearby mid- and
upper-level ridge supporting a strong subsidence inversion.
Clear and mostly dry conditions will prevail through tomorrow
morning, except for some showers near Kona this evening, and a few
brief showers over windward Big Island later tonight.
While little overall change to the weather pattern is expected over
the next couple of days, a subtle decrease in wind speed is
anticipated as the ridge is pushed a little closer to Kauai by a
rapidly strengthening low passing far N of the area. So while the
trade wind flow may have been a little stronger than expected today,
thereby preventing significant leeward sea breezes/clouds, we may
see a few more afternoon leeward clouds Monday and Tuesday as winds
diminish. Leeward clouds or not, significant rainfall is not
expected as the island atmosphere will remain stable and mostly dry.
Nights and mornings will be mostly dry.
A new high building N of the area will bring increasing trade winds
Wednesday/Thursday that will persist into next weekend, delivering
what is expected to be only brief windward showers. Leeward Big
Island will see afternoon clouds and showers, that will linger
through the evening hours, and sometimes into the early morning.
Worth noting that while most of the state is entering the dry
season, it is the wet season for leeward Big Island. Interestingly
1.68" of rain has been recorded at PHKO in the last 24 hours,
mostly due to a soaking heavy shower around 3 am last night.
High clouds near the Big Island are expected to spread over the
other islands beginning Monday night, potentially persisting for
several days. If guidance continues this trend, sky cover will be
increased in the forecast.
A strong ridge of high pressure to the north of the islands will
maintain light easterly flow across the state. Light sea breezes
will predominate most areas in the afternoon and early evening hours
while weak land breezes will be the rule in the late night and
The air mass over the state remains mostly dry and mostly stable.
Shower activity will be limited and will occur mainly over island
interiors during the afternoon and evening hours. Isolated MVFR CIG
and VIS are possible in brief showers. Otherwise, VFR conditions
will prevail all areas.
No AIRMETs are in effect or anticipated at this time.
A surface ridge about 270 nm north of Kauai will continue to
drift slowly toward the south during the next couple of days. This
will maintain moderate easterly trade winds around the Big Island
and Maui, with weaker east-southeast background flow from Molokai
to Kauai. Stronger high pressure is forecast to develop far north
of the state Wednesday, which will cause the easterly trade winds
to strengthen from mid-week through Friday. There are no Small
Craft Advisory conditions in the current forecast this week.
South facing shores will see periods of surf around the May
average through much of the week. A longer period south-southwest
swell will likely combine with a small south-southeast swell to
produce moderate sized surf near or just below the May average
through the Memorial Day Holiday, followed by a slight drop on
Tuesday and Wednesday. Another pulse of south-southwest swell
energy is expected from late Thursday through Saturday.
Small north-northwest swells are expected to produce surf near
the May average along most north facing shores of the smaller
islands through mid-week. The small northwest swell will
eventually shift out of the north from Thursday night through
Surf along east facing shores will likely remain below the May
average this week due to the weaker than normal trade winds in
the vicinity of, as well as upstream of the state.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office