Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 241406

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Sun Sep 24 2017

Trade winds will gradually ease during the next couple of days as a
surface ridge to the north weakens. Mainly windward clouds with
passing showers will prevail through Tuesday. A possible boost
in shower activity is expected around Wednesday as moisture from a
dissipated surface trough is forecast to reach the state from the
east. Gentle trade winds will likely persist for the later part of
the week.


Gentle to moderate trade winds continue across the islands early
this morning as a surface high and its associated ridge stay far
northeast and north of the area respectively. A little more low
clouds have reached the islands from the east, bringing some showers
affecting mainly windward areas. Early morning Lihue sounding
revealed a rather dry but slightly unstable airmass, while Hilo
sounding is a little more stable but with more low level moisture.
Expect trade wind weather to prevail today, with passing low clouds
and showers affecting windward areas. Lee areas of the Big Island
will see afternoon and evening clouds and showers.

Slow changes to the ongoing weather pattern are in store for the
islands though the next few days. High far northeast as well as its
associated ridge will slowly weaken as a cold front from the far
northwest advances east. This will lead to a gradual decrease in the
trades across the islands. With the lighter trade winds, sea breezes
over the lee areas will become more prominent, with more afternoon
clouds possible over the lee areas. Meanwhile, passing low clouds
embedded in the weakened trade wind flow will continue to reach the
area, bringing some showers to the windward areas at times. There
will be enough pressure gradient across the state for the gentle
trade winds to persist through the later part of the work week.

Moisture associated with a weak surface trough far east of the state
is expected to reach the area by Wednesday. This will probably lead
to an increase in shower activity for the islands, but then latest
forecast solutions still indicate a weak upper level ridge may move
to the north of the state, with airmass in the island vicinity
staying slightly stable. This may put a slight damper on the shower


High pressure northeast of the State will keep a light to moderate
trade wind flow in place through tonight, with clouds and showers
favoring windward and mauka areas. Brief MVFR cigs/vsbys will be
possible in passing showers across windward areas, but predominantly
VFR conditions are expected through 12Z Monday.

No AIRMETs are in effect and none are anticipated today.


Trade wind speeds will remain below the Small Craft Advisory
threshold through the forecast period.

Surf along south facing shores will remain small through early this
week, with mainly background southeast and southwest swell energy
expected. Although a small, long-period pulse out of the southwest
from the Tasman Sea is expected today, it will only result in a
slight increase in south shore surf. For the extended forecast,
strong to gale-force southwest winds associated with another low in
the Tasman Sea may lead to a reinforcing, small southwest swell by
Tuesday and extending through midweek.

A small northwest swell will subside through today, before another
small reinforcement from that direction fills in beginning tonight,
lasting through the middle of the week.





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