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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 191325
Area Forecast Discussion
National Weather Service Honolulu HI
325 AM HST Fri Apr 19 2019
A ridge of high pressure north of the state will keep moderate to
locally breezy trade winds in place through the weekend and much
of next week. Fairly dry trade wind weather will prevail through
the period, with clouds and showers limited primarily to windward
and mauka areas.
Currently at the surface, a 1029 mb high is centered around 1500
miles north-northeast of Honolulu, with ridging extending
southwestward from the high to a location around 350 miles north
of Kauai. The resulting pressure gradient is driving moderate
trade winds across the island chain early this morning. Infrared
satellite imagery shows clear to partly cloudy skies in most
areas, with patches of more extensive cloud cover in some windward
locales. Radar imagery shows a few showers moving into windward
areas, with mainly dry conditions in leeward sections. Main short
term focus revolves around rain chances.
A ridge of high pressure will prevail to the north of the state
through the weekend and much of next week, keeping the trade
winds blowing across the island chain. There could be a slight
increase in trades over the weekend as the surface ridge axis
lifts a bit further northward, but generally moderate to locally
breezy trades should prevail. Upper level ridging will keep the
airmass stable and rather dry with precipitable water values
remaining at or below seasonal levels. As a result, expect fairly
dry trade wind weather to prevail through the period, with showers
confined primarily to windward and mauka areas. Leeward sections
should remain dry most of the time, with isolated showers confined
mainly to the overnight and early morning hours.
A high pressure ridge north of the state will keep the islands in
a moderate to breezy trade wind weather pattern into the weekend.
Near surface wind speeds are strong enough to support moderate
low level turbulence over and south through west of mountain ranges
of all islands. Scattered shower activity will favor windward and
mountain sections with brief periods of MVFR conditions mainly
during the overnight hours.
AIRMET Tango remains in effect for tempo moderate turbulence below
080. This AIRMET will likely remain in effect through the
No significant changes to the forecast this morning. Fresh to
strong trades will continue into early next week as a ridge
remains north of the islands. The Small Craft Advisory (SCA)
remains posted for the typical windier areas near Maui County and
the Big Island through Sunday afternoon. Some of the models show
an uptick in the winds tomorrow which could mean some additional
areas near Maui County and the Big Island may need to be added to
the SCA. At this time going to see how things pan out today and
tonight before adding them in. Its possible that the SCA for the
existing areas will be extended into next week.
The current north-northwest swell is expected to peak today below
advisory levels, and then slowly decline through the weekend. A
small, west-northwest swell will be possible early next week,
again expected below advisory levels.
Background south-southwest swells will keep small surf along south
facing shores through the weekend. An upward trend is expected early
next week, as early as Sunday night, due to activity south to
southeast of New Zealand over the past few days. Guidance depicts
this source peaking at Pago Pago Saturday, which should correlate
to above average south shore surf continuing into midweek.
Surf along east facing shores could see a bump over the weekend
with an uptick in the trades.
See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office