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Temp7.8 C
RH20 %
WindNE 16 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 201947

Area Forecast Discussion
National Weather Service Honolulu HI
947 AM HST Fri Jul 20 2018

A trade wind weather pattern can be expected over the next several
days thanks to high pressure far north northeast of the area.
Clouds and passing showers will tend to favor windward and mauka
areas. Some increase in shower activity is expected late Sunday
through Tuesday as an area of enhanced moisture embedded in the
trades moves westward across the area.


High pressure is centered far to the north northeast of the state
with a weak area of low pressure moving westward several hundred
miles south of the state. The pressure gradient between the two is
producing moderate to locally breezy trade winds across the area.
Moisture embedded in the trades is providing for a few light
passing showers over windward and mauka areas while most leeward
locations remaining dry. Southwesterly flow in the upper levels
of the atmosphere are drawing up some high cirrus clouds across
the area which may dim the sunshine at times today.

The low to the south of the state is forecast to continue moving
west and weaken over the next couple of days. This will cause a
slight drop off in trade wind speed's from current levels. A
stable airmass over the area will continue to keep shower activity
at a minimum through early Sunday.

An area of enhanced moisture is seen on satellite imagery centered near
20N140W. Models are in general agreement on this area of moisture
arriving over the east end of the island chain Sunday afternoon or
Sunday night. This area will pass eastward across the state Sunday
night through Tuesday. Shower activity will increase with is
passage primarily over windward and mauka areas. Showers chances
may also increase during the afternoon hours over the Kona slopes
with a few passing showers also possible over some other leeward
areas. The airmass is expected to remain on the stable side so
heavy showers are not expected.

A trade wind weather pattern is then expected to continue through
the remainder of the week. Trade wind speeds will generally blow
at moderate levels with clouds and passing showers favoring
windward and mauka areas.


High pressure north of the state will keep a moderate to locally
breezy trade wind flow in place through Saturday. Clouds and
showers will favor windward and mauka areas, primarily during the
overnight and early morning hours. Some brief MVFR cigs/vsbys will
be possible in these passing showers, but predominantly VFR
conditions are expected over the next 24 hours.

No AIRMETs are currently in effect.


Moderate to locally strong trade winds continue. A disturbance
located about 500 miles southwest of Hawaii will continue to track
west and away from the islands today. The Small Craft Advisory
(SCA) remains in effect through this afternoon for the typically
windier waters around the Big Island and Maui County. The passing
of this disturbance has helped to tighten the local pressure
gradient over the state, but this will begin to weaken as the
disturbance tracks farther from the state. Winds are then expected
to decline a notch by tonight, likely below SCA thresholds.
Another weak disturbance is then forecast to pass south the of
state early next week, once again tightening the pressure gradient
over the state, leading to an increase in winds and seas.

A series of reinforcing south-southwest swells will keep surf
along the south facing shores slightly above the summer average
through tonight. A larger and longer period south-southwest swell
is expected to begin filling in Saturday and peak later Sunday.
This swell may cause surf to approach the High Surf Advisory (8
ft) threshold along south facing shores from Saturday into Monday.

See the latest Oahu Surf Discussion (SRDHFO) for additional details
on surf and swell.


Small Craft Advisory until 6 PM HST this evening 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