598
FXHW60 PHFO 241400
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Sun Aug 24 2025

.SYNOPSIS...
Hawaii will remain under the influence of high pressure ridging
to the north and east as a trough lingers north of the state.
This will result in light to locally breezy trade winds today.
There will be a slight drop off in wind speeds tomorrow in response
to the trough sagging south and weakening the downstream pressure
gradient. Generally a dry, stable and very warm summer weather
pattern will prevail with only occasional light windward mauka
trade showers. The lone exception will be scattered afternoon and
evening showers over the Kona slopes of Big Island the next couple
of days.


&&

.DISCUSSION...
Mid to upper level ridging centered north and east of the islands
will be the main control to persistent warm and dry conditions. A
500 mb 589 dam high pressure ridge, with the 1023 mb surface high
centered 1,200 miles from Hilo, is resulting in a stable late
August dry trade wind weather. Early morning satellite trends
verify these stable conditions with widely-scattered warm low
topped clouds moving in on generally moderate to fresh easterly
trade flow. 12Z local soundings depict a strong 5-7k ft trade
inversion height and below normal near one inch precipitable
waters (pwats) in Hilo (falling into the lower quartile for this
time of year). A higher ribbon of moisture expanding up from the
south-southwest into the far western end of the state this morning
has Lihue at near normal 1.41 inch pwats. A northern trough axis
will settle south and weaken the pressure gradient over the region
enough to allow trades to fall back to more light to moderate
speeds the next couple of days. Rainfall has been nearly non-
existent across most windward areas and, other than a few showers
developing along the Kona slopes of Big Island and within the
smaller island windward mauka regions, leeward areas will remain
dry this week. There will be little variance in the Central
Pacific synoptic pattern the next several days so these summertime
conditions will be the general theme through the remainder of
August.

The southern approach of a northern trough axis will reach the
state`s northern offshore waters tomorrow and Tuesday. This will
weaken the northeast-to-east ridge enough to cause a brief
interruption to recent moderate to locally strong (oceanic) trade
flow. Monday through Wednesday`s weakened winds will veer a bit
more to the east southeast. Shortwave energy diving down around
the base of the trough later in the week will assist in keeping
stronger trades at bay through the last few days of the month.
Weaker trade flow will allow local breezes to become more dominant.
Thus, early sun will likely lead to mid to late afternoon into
early evening cloud build up and scattered showers over Big Island
Kona and upslope leeward mauka over Oahu and Kauai. Models are
forecasting a minor increase in moisture moving up from the
southeast and passing across Big Island tomorrow through Tuesday.
This higher surge of moisture through a deeper boundary layer may
enhance afternoon Kona slope showers early this week. The mid
layers remain very dry across the remainder of the chain so, other
than localized afternoon breeze activity, the only other rain
producer would have to be from brief terrain-enhanced windward
upslope mauka showers.


&&

.AVIATION...
Stable, moderate to breezy trades deliver clouds and showers
windward and mauka through the period particularly overnight and
during the early morning hours. Isolated MVFR within showers.
Otherwise, VFR prevails.

No AIRMETs are in effect.


&&

.MARINE...
A ridge of high pressure north of the Hawaiian Islands will
continue to produce fresh to locally strong trades today. A Small
Craft Advisory (SCA) remains in effect for the windier waters of
Maui County and the Big Island through 6 PM.

Small overlapping south swells and surf heights will continue to
slowly decline into Monday. A series of small long period south
swells will arrive by Tuesday, boosting south shore surf heights
through Friday.

Surf along north and west facing shores will remain nearly flat
while surf along east facing shores will continue to have trade
wind driven chop for the next few days.


&&

.FIRE WEATHER...
The lack of rain and lower humidity will maintain elevated fire
weather concerns this weekend. Other than the typical high terrain
channeled winds, many locations will experience light to low end
moderate trades or afternoon sea breezes/overnight land breezes.
While many will experience afternoon humidities falling under 50
percent, lighter winds should hold Red Flag Warning (RFW)
conditions at bay. These dry conditions have placed the majority
of the state in a moderate to severe drought. Thus, regional scale
winds will need to be the parameter that is most closely
monitored in a potential RFW situation. Inversion heights will
undergo little change so the main driver of wind will be supported
in the large scale. Wind speeds are expected to fall off early
next week in response to a northern trough weakening the gradient
produced by eastern high pressure. As this trough pulls back
further north at mid week, trades may slightly increase to more
typical moderate speeds Wednesday.

&&

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


&&

$$


DISCUSSION...Blood
AVIATION...Blood
MARINE...Walsh
FIRE WEATHER...Blood