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Hawaiian Islands Synoptic Discussion and Guidance

140
FXHW60 PHFO 191335
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
335 AM HST Sat Oct 19 2019

.SYNOPSIS...
Trade winds will continue through the weekend and much of next
week, delivering clouds and showers to windward areas, with a
stray shower reaching leeward locales from time to time. High
clouds of varying thicknesses will occasionally move over the
islands through early next week.

&&

.DISCUSSION...
Currently at the surface, a 1027 mb high is centered around 1100
miles northeast of Honolulu, while the northern extent of a weak
trough of low pressure is located around 150 miles south-
southeast of the Big Island. The resulting gradient is producing
moderate trade winds across the island chain early this morning.
Infrared satellite imagery shows low clouds moving into windward
areas with the trades, with high clouds associated with a jet
stream aloft spreading from southwest to northeast across the
state. Radar imagery shows scattered showers moving into windward
areas, with a stray shower drifting leeward from time to time.
Main short term concerns revolve around rainfall chances and
trade wind trends over the next several days.

Trade winds will prevail for the next 7 days, with only some minor
fluctuations in speed expected. Moderate to locally breezy trades
will hold in place today and tonight, then ease slightly Sunday
through Monday as a weakening cold front approaches from the
northwest. The trades are expected to edge up Monday night through
Wednesday as high pressure northeast of the state strengthens,
before trending back down late next week as a new cold front
approaches from the northwest.

Fairly typical trade wind weather is expected to continue during
the next 7 days, with showers favoring windward and mauka areas
along with the occasional leeward spillover. Showers are expected
to be most common between 6 PM and 10 AM each day. Shower coverage
through the weekend and into Monday is expected to be lower than
normal, as the airmass remains fairly dry and stable. Slightly
higher precipitable water values move in late Monday and remain in
place through the end of the work week. This should increase
shower coverage to more typical levels for this time of year.

Periods of high cloud cover associated with a jet stream aloft
will continue to move overhead through the weekend and into early
next week, resulting in partly to mostly cloudy conditions. The
high clouds should thin out Tuesday through late next week.

&&

.AVIATION...
Moderate to breezy easterly trade winds will continue through
this evening, then shift out of a more east-southeast direction
late tonight through Sunday. Clouds and showers will favor
windward and mountain locations, with the best coverage likely
occurring through the overnight and early morning hours.

No AIRMETs are in effect or anticipated at this time. Brief MVFR
ceilings and visibilities are possible in and around passing
showers. Otherwise, VFR conditions will prevail for all areas.

&&

.MARINE...
High pressure northeast of the state will maintain fresh to
strong easterly trade winds through at least tonight, so the
Small Craft Advisory (SCA) has been extended for the typical
windier waters near Maui County and the Big Island.

As a front moves closer to the state from the north late tonight,
winds are expected to shift to the east-southeast. The front is
expected to stay north of the islands, and will likely weaken the
winds over the western half of the coastal waters. Winds are
expected to shift back to a more easterly direction Monday.

Surf is expected to remain below advisory levels through the
forecast period. The current combo north and northwest swell will
continue to gradually decline through the weekend. A small
reinforcement from the north-northwest is possible today. A gale
low is expected to develop near the Kurils tonight into Sunday,
and then track to the east toward the Date Line Sunday into
Monday. This would generate a northwest swell that could reach the
islands late next week.

Last week, a storm force low far southeast of New Zealand tracked
east with a captured fetch aimed east of the state. Buoy 51004
southeast of the state, is showing an increase in energy this
morning. Near-shore buoys are also registering an increase in
long-period energy. We should see a gradual rise in surf along
south facing shores today as the small south swell fills in. Surf
should be around the summer average over the weekend, before
slowly dropping off early next week.

The fresh to locally strong trade winds will maintain rough surf
along east facing shores through most of the weekend and into
early next week. A slight decrease is possible Sunday as winds
briefly decrease, but choppy rough surf will quickly return as
trades restrengthen early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Gibbs
MARINE...Kino

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



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