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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 291954

Area Forecast Discussion
National Weather Service Honolulu HI
954 AM HST Fri Sep 29 2023

Moderate to locally breezy trade winds will deliver passing
clouds and showers, mainly to windward and mauka areas, through
the weekend. Elevated dewpoints today will make it feel muggy this
afternoon afternoon. Light winds and mostly dry weather are
expected next week, with limited showers focused over interior
areas during the afternoon.


No change to the forecast this morning, and little change is
expected with the afternoon package. A high pressure system
remains centered far north-northeast of the islands, driving trade
winds over the islands. A pair of lows far to the northwest and
west-northwest will move to the east over the coming days,
disrupting the high and putting an end to the trade winds. As the
high moves to the east, winds are expected to turn to the
southeast and weaken.

Showers being carried in on the trades will continue to be focused
over windward and mauka areas today and tomorrow, however low
clouds are beginning to move in from a slightly south of east

Dewpoints have climbed into the 70s in many locations across the
state, which has contributed to heat indices already reaching into
the low to mid 90s in some locations. Expect temperatures and heat
indices to rise this afternoon during the heat of the day.
Dewpoints are expected to a bit lower tomorrow.

Near normal precipitable water (PW) is expected today and
tomorrow, but looks like a decrease Sunday onwards. Satellite
derived PW shows the near normal PW extending about 500 miles to
the northeast of the islands, with drier air beyond that. As we
head into next week, low pressure will move to the east and
replace the high currently to our north-northeast. As that
happens, the ridge will sink southward near or over the islands,
resulting in weaker winds for much of the week. Expect a land and
sea breeze pattern to set up. With limited moisture available,
clouds are expected during the afternoon hours, but expect limited
shower activity.

A weak front associated with the low looks to move close to Kauai
from the north midweek. Most ensemble members stall this moisture
boundary to the north of Kauai during the second half of the week.
This would keep a mostly dry airmass over the islands. Light
winds look likely in the long term as well as low pressure remains
north of the region.



Moderate to locally breezy trade winds will continue today.
Clouds and showers will generally favor windward and mountain
locations, with greater coverage and intensity overnight into the
early morning hours. Periods of MVFR ceilings and visibilities
will be possible in some of the heavier passing showers.

AIRMET Tango remains in effect for tempo moderate turbulence below
9000 feet for areas downwind (south through west) of island terrain.
This AIRMET will likely remain in effect through most of the
weekend before conditions improve early next week.



Locally strong easterly trade winds will continue through the
weekend. The Small Craft Advisory for the windier waters of Maui
County and the Big Island remains in effect through this time.
Governing high pressure will weaken considerably early next week
resulting in light trades by Monday and southeast or variable
winds thereafter.

Surf along north-facing shores remains small into the weekend. A
pair of systems moving eastward toward the Aleutian Island Chain
and the Gulf of Alaska during the next several days will result in
a period of increased surf along the north shore beginning Sunday.
First, a small, medium period NNW (330) swell builds during
Sunday and peaks Sunday night into Monday, lingering through
Tuesday. Then a slightly larger and longer period NW (310-320)
swell builds through Tuesday and peaks during the middle of next

Short period, choppy surf along east-facing shores will trend down
next week as trades weaken or die altogether. South-facing shores
remain small through mid-week as background southwest and
southeast swells fill in.


Small Craft Advisory until 6 PM HST Saturday 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