Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 04/06/2026 05:03:00 PM UTC

                        
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FXHW60 PHFO 060703
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
903 PM 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 expected by Tuesday as an
upper disturbance and surface low pressure evolve northwest of the
islands. This system is forecast to draw deep tropical moisture
northward over the state, leading to an extended period of
southerly winds, increased chances for widespread rainfall, and
renewed flooding concerns from the middle of the week through the
weekend.

&&

.SHORT TERM UPDATE...
Issued at 836 PM HST Sun Apr 5 2026
A diffuse band of scattered showers caught up in the trades lies
over and to the east of Oahu this evening. As the trades continue
to veer and weaken, HREF and REFS both show this band slowly
beginning to pull west-northwestward and slowly expanding overnight,
eventually including mainly windward and mauka sections of Kauai
as well. With little upper support, these showers will not amount
to too much.

A digging shortwave trough east of Midway tonight will push
rapidly ESE down the Northwest Hawaiian Islands through Monday.
The high resolution ensembles show the trough aloft should be
close enough to begin locally enhancing showers over and near
Kauai Monday night in the SE flow. A few of these might become
briefly heavy as this leading shortwave gets close and mid-level
temperatures cool for a while, but instability will still be
limited at this point.

&&

.PREV DISCUSSION...
Issued at 417 PM HST Sun Apr 4 2026
This afternoon, relatively quiet weather continues across the
islands with only a few light showers embedded within moderate
trade winds noted in regional satellite and radar imagery. In
addition, the typical dayThe latest high resolution
guidance shows that atime increase in cloud cover has occurred
over the Kona slopes of the Big Island, though little to no
shower activity has been observed there today. Moderate easterly
trade winds will continue to focus mainly light showers along
windward and mauka slopes, while leeward areas remain mostly dry
through Monday.

By Monday night, trade wind flow will be disrupted as the surface
ridge to the north erodes and a broad surface trough develops
northwest of the islands. As a result, weaker background surface
winds will begin to veer out of the southeast to south from
Tuesday through Wednesday. Guidance indicates that this also will
mark the beginning of a series of shortwave troughs that are
expected to dig southeastward towards the main Hawaiian Islands
in what will be a notable amplification and shift in the large
scale pattern across the Central Pacific for the rest of this
week. As background flow becomes more southerly, models remain in
good agreement that deep tropical moisture will be drawn northward
once again over the islands as early as Tuesday but especially by
Wednesday. 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 afternoon.

From Wednesday through the end of the week, potential for more
widespread rainfall and flooding will return. 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
southerly winds (which could be gusty at times) all point towards
yet another widespread and organized rainfall event for the state.
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.

There remain some differences among global models by next weekend,
but the general consensus is that the active pattern could
linger, with the potential for rain across at least portions of
the state persisting through the weekend and beyond where the deep
moisture axis anchors.

As previous discussion have mentioned, one important consideration
with this week`s rainfall is antecedent conditions. The islands
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 high
rainfall rates could quickly lead to enhanced runoff, renewed
rises in streams and reservoirs, and localized flash flooding
concerns.

Some tweaks have been made with this afternoon`s forecast updates,
primarily for QPF and timing. This system will continue to be
monitored closely over the coming days, and additional adjustments
to timing, duration, and impact messaging are possible as details
become more clear.

&&

.AVIATION...
Issued at 417 PM HST Sun Apr 4 2026
Mild to locally breezy trades will continue to prevail through
the period. Periodic shower activity along windward sites may
briefly bring conditions down to MVFR, however widespread VFR
conditions are generally expected. Winds are expected to shift
more east and even southeast during the day tomorrow across the
islands.

No AIRMETS are in effect and none are expected through the next 24
hours.

&&

.MARINE...
Issued at 417 PM HST Sun Apr 4 2026
Moderate to locally fresh trades will persist for the next day or
so 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.

Small northwest swells will keep some small surf along north
facing shores through Monday. A moderate long-period northwest
swell will fill in Monday night and Tuesday, giving more of a
boost to north shore surf late Tuesday through Wednesday.

A small southerly swell will keep some small surf in place along
south facing shores through Monday. A slightly larger, long-period
south swell, will fill in Monday night. This swell will give a
more noticeable increase to south shore surf Tuesday into next
weekend. Strengthening southerly winds could make for choppy seas
by late next week.

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

&&

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

&&

$$

SHORT TERM...R Ballard
DISCUSSION...Vaughan
AVIATION...Evans
MARINE...TS