Waipahu, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

312
FXHW60 PHFO 051304
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
304 AM HST Sun Apr 5 2026

.SYNOPSIS...
Mostly dry and pleasant trade wind weather will continue into
Monday, with brief passing showers favoring windward and mauka
areas. A significant pattern change is then expected by Tuesday
as an upper disturbance and surface low pressure evolve northwest
of the islands. This system is expected to draw deep tropical
moisture northward over the state, leading to an extended period
of southerly winds, increasing chances for widespread rainfall,
and renewed flooding concerns from Tuesday through next weekend.

&&

.DISCUSSION...
A relatively benign trade wind pattern remains in place across
the Hawaiian Islands this morning and is expected to persist into
Monday. Moderate easterly trades will continue to focus mainly
light showers along windward and mauka slopes, while leeward areas
remain dry.

Global guidance remains in good agreement and depicts a notable
amplification of the large-scale pattern across the central
Pacific by Tuesday. A series of shortwave troughs digging
southeastward toward the state will translate to large-scale upper
height falls a cross the region. The surface ridge to the north
will gradually erode as an attendant broad surface trough evolves
to the west. This will disrupt the typical trade wind flow by
Monday night and allow low-level winds to gradually veer out of
the southeast to south Tuesday through Wednesday.

This transition to southerly flow will draw deep tropical moisture
northward into the islands beginning Tuesday and especially by
Wednesday. Precipitable water values are forecast to climb toward
2 inches or higher, signaling a marked increase in moisture. This
increasing moisture combined with daytime heating, sea breezes,
and a potent shortwave trough moving through may even trigger some
heavy showers over interior areas on Tuesday.

Confidence is increasing that the second half of the week may
present the highest potential for widespread rainfall and flooding
impacts across the state. During this time, upper-level forcing
is expected to strengthen as a strong shortwave rounds the base of
the trough, potentially enhancing lift over the region while low
pressure organizes west of the islands. The combination of deep
moisture, increasing large-scale forcing for ascent, and gusty
southerly winds favors a transition toward a more widespread and
organized rainfall event. In addition to the rainfall concerns
during this period, some strong to severe thunderstorms along with
gusty downsloping winds for north and windward sides of the
islands can`t be ruled out.

Although forecast confidence begins to lower by next weekend due
to model differences, the general large-scale pattern could
linger. This scenario suggests the potential for rain may persist
through next weekend and beyond for at least parts of the state
or where the deep moisture axis anchors.

Regardless of the precise evolution, antecedent conditions remain
a significant concern. The islands have experienced significant
flash flood events in recent weeks, and despite several days of
drier trade wind weather, soils remain vulnerable in many areas.
As a result, any period of heavy rainfall may quickly lead to
enhanced runoff, renewed rises in streams and reservoirs, and
localized flash flooding concerns.

This system will continue to be monitored closely over the coming
days, as additional adjustments to timing, duration, and impact
messaging are likely as this change in the pattern evolves.

&&

.AVIATION...
Moderate trade winds will continue today and tonight. Isolated
light showers will focus mainly on windward slopes, with brief
MVFR conditions are possible. Otherwise, VFR conditions are
expected to prevail.

No AIRMETs are in effect and none are expected today.

&&

.MARINE...
Moderate to locally fresh trades will persist during the next
couple days as high pressure north of the islands moves slowly
eastward. Winds will ease and shift southeasterly Monday night
through Wednesday as a front stalls out and merges with a trough
just west of the islands. The winds will turn more southerly and
increase to moderate and strong levels on Thursday as a storm
system develops along the trough west of the state.

A series of overlapping small northwest swells will keep some
small surf in place along north facing shores through Monday. A
new long-period northwest swell will fill in Monday night and
Tuesday, giving a more noticeable boost to north shore surf late
Tuesday through Wednesday, followed by a gradual decline Thursday
into next weekend.

Overlapping southerly swells will keep some small surf in place
along south facing shores through Monday. A new long duration,
and slightly larger long-period south swell, will fill in Monday
night. This swell will give a more noticeable boost to south
shore surf Tuesday into next weekend. Strengthening southerly
winds could lead to choppy conditions by late next week.

East shore surf will remain small and below climatological levels
during the next 7 days due to a lack of strong trade winds over
and upstream of the islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Gibbs
AVIATION...Parker
MARINE...Jelsema