422
FXHW60 PHFO 051405
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
405 AM HST Thu Jun 5 2025

.SYNOPSIS...
A weakly unstable cloud band associated with the remnants of an
old East Pacific cold front are drifting through the islands this
morning. An upper level disturbance west of Kauai will help to
enhance shower activity through the early morning hours across
the islands. A general troughing pattern at lower and upper levels
will keep periods of showers in the forecast mainly in the
overnight to early morning hours through Monday morning with more
stable trends during the day. More stable trends develop from
Monday onward as a high pressure ridge builds in over the state.
Easterly trade winds will prevail in the moderate to breezy range
today with a slight decrease in wind speeds to more moderate
levels from Friday through early next week.

&&

.DISCUSSION...
An interesting picture in our weather pattern starts with
satellite imagery this morning. A combination of low and upper
level forcing will keep wet trends in the forecast across the
state this morning. In the lower levels, a long cloud band
associated with an old East Pacific frontal boundary drifts
westward into the islands on the trade winds. This band will
likely clear the island chain just before noon HST today with
a notable decrease in daytime shower trends. In the upper levels,
a weak upper low remains in place just west of Kauai, some upper
level divergence and lingering instability over the islands will
help to lift cloud heights over the region into Friday. Shower
trends will tend to favor the typical windward and mountain areas
in the overnight to early morning hours.

The latest weather forecast guidance showers a general upper
level troughing pattern over the state into Monday morning.
Starting with the upper low currently west of Kauai, this low will
begin to drift northeastward and weaken through Friday. However a
cyclonic general troughing pattern remains in place, which will
keep brief passing showers in the overnight to early morning
windward and mountain, and brief showers over island interior
sections during the day are in the forecast through the weekend.
On Monday this upper level pattern changes to a more stable
environment, as an upper level ridge moves over the state and the
temperature inversion heights drop to around 5,000 to 6,000 feet
through much of next week.

In our wind forecast guidance, we see moderate to breezy easterly
trades will continue into the overnight hours. These easterly
trade winds decrease slightly into the light to moderate range
starting on Friday as the high pressure ridge north of the state
weakens in response to a migrating low pressure system slowly
drifting across the North Pacific. Some expansion of daytime sea
breezes along terrain sheltered western island slopes should be
expected during this time period. This means a hybrid trade wind
sea breeze weather regime will take hold over each island with
brief afternoon showers possible over island interior sections
this weekend due to the lingering troughing environment and low
level wind convergence bands forming along trade wind and sea
breeze boundaries.

&&

.AVIATION...
A long cloud band currently drifting westward through the islands
will keep showers in the forecast, mainly over windward and
mountain areas. Brief MVFR conditions are possible in showers this
morning. Expect This cloud band to drift west of most islands
later this morning with improving weather trends. Overnight to
early morning hours will bring a return to brief periods of MVFR
conditions in showers, mainly over windward mountain slopes.

Around 10:25 PM HST (8:25Z) on Wednesday night our local doppler
radar detected a plume of volcanic ash quickly rising above the
Halemaumau Crater at the Kilauea volcano. This ash plume swiftly
rose to around 18,000 feet elevation and the easterly trade winds
kept the ash cloud fairly localized to areas near the crater and
immediately southwest through west of Halemaumau. The latest
radar imagery shows this ash plume has decreased in intensity and
the plume height has fallen to around the 8,000 foot level.

AIRMET Tango remains in effect for low level moderate turbulence
over and immediately south through west of island mountains due to
moderate to breezy trade winds. This AIRMET will likely be
cancelled later tonight as the trade wind speeds decrease.

&&

.MARINE...
Moderate to locally strong trades will gradually ease today, becoming
gentle to fresh by Friday in response to weakening high pressure
northeast of the state. Gentle to fresh trades prevail Friday into
early next week then restrengthen as the seasonal high redevelops.
Small Craft Advisory has been extended through 6 am Friday as
locally strong winds hold through the day and into the evening
hours.

Tiny to small, long period southwest swell will hold today maintaining
small surf along favored exposures. Forerunners from a moderate,
long period south southwest swell originating from an extratropical
cyclone east of New Zealand will gradually fill in tonight into
Friday. This swell will peak over the weekend near or above the
High Surf Advisory threshold before slowly fading early next week.

Choppy surf along east facing shores will hold into the weekend
even though locally induced tradewind swell will be on the
decline. This is thanks to a low that developed near the
California coast earlier this week which is sending a moderate,
medium period northeast swell later today and should peak Friday
before fading Saturday. Surf along north facing shores will remain
small.

&&

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

&&

$$

DISCUSSION...Bohlin
AVIATION...Bohlin
MARINE...Almanza