Royal Kunia, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

730
FXHW60 PHFO 191341
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
341 AM HST Thu Mar 19 2026

.SYNOPSIS...
A kona low system will move in from the west today, expect
increasing showers and thunderstorms with southerly winds
affecting each island starting tonight and lasting through the
weekend. The threats for heavy rain and thunderstorms will become
widespread, with each island affected by pulses of showers through
the event as multiple surface lows pass just north of the island
chain. A combination of low level forcing and passing upper level
troughs will drive the smaller scale heavy rain band and
thunderstorm formation. Improving weather trends will develop from
west to east on Monday as we transition to a wet trade wind
weather pattern lasting through the end of next week.

&&

.DISCUSSION...
Deep cloud cover continues to develop over the Hawaii region this
morning in response to a low pressure system moving in from the
west with upper level troughing and sub tropical jet stream
support. Winds will veer more southerly tonight as shower
activity slowly increases across the state, pulling up additional
moisture from the deep tropics, ahead of the approaching kona low.
Two weak surface lows, supported by upper level troughing, will
drift through the islands from later tonight through Sunday. The
large scale forcing will move the heaviest showers to different
islands in pulses of activity throughout this event.

A Flood Watch remains in effect for most of the Hawaiian Islands
for this event. This watch may be expanded statewide as run to run
model guidance continues to show differences in where and when
the heaviest showers may develop.

The first pulse of increasing moderate to heavy showers and
thunderstorms will move in ahead of the first surface low passing
just north of the island of Kauai from tonight into Friday. The
latest weather model consensus shows the best forcing for
increasing moderate to heavy shower activity develops along a wind
convergence band favoring the islands in Maui County and Oahu.
The next pulse shifts into gear from Friday night into Saturday as
the next surface low moves northeastward passing just north of
Kauai. The band over Maui County shifts northward to Kauai, Niihau
and Oahu during this time period. Stronger upper level dynamics
from a passing trough, bulk wind shear from 35 to 50 knots and
instability suggests stronger rotating thunderstorms will likely
develop near the western islands. Kauai County may see increasing
chances for heavy showers and thunderstorms from Friday night into
Saturday.

By Sunday, the surface low rapidly moves away from the Hawaiian
Islands towards the northeast direction. Cool northerly to
northeasterly winds begin to filter into the western islands of
Niihau, Kauai and Oahu with drying trends by Sunday night. Western
islands in Maui County and the Big Island will continue to see
periods of moderate to heavy showers.

On Monday, the heavy shower and thunderstorm threat ends as we
quickly transition back to a northeasterly trade to last into
Thursday with wind pattern. Cooler temperatures are expected to
last into Thursday with enhanced showers due to a weak upper level
troughing pattern, showers will favor the typical windward and
mountain areas into next weekend.

&&

.AVIATION...
Conditions will gradually deteriorate through the day as an
upper-level disturbance and surface low approach from the west.
Expect increasing chances for widespread rainfall across portions
of the state. The low-level flow will gradually veer from the
southeast today to south-southwest by Friday, with speeds
increasing into the moderate range at exposed terminals. Expect
periods of MVFR/IFR CIGS/VSBYS, especially in showers.

AIRMET Sierra for mountain obscuration can also be expected for
much of the area by tonight. AIRMET Tango is in effect for
moderate turbulence for FL200-350. These conditions are expected
to persist today. AIRMET Zulu for light icing in layer 150-FL250
is also anticipated.

&&

.MARINE...
Light to locally fresh east to southeast winds will slowly
strengthen to moderate speeds and veer south by Friday as a ridge
strengthens northeast of the state and a broad area of low
pressure develops west of the state. The low will strengthen over
or near the far northwest offshore waters on Friday before lifting
northeast on Saturday. Winds will shift out of the south
southwest during this time at moderate speeds. On Sunday, winds
will become light and variable for a brief time as the low exits
to the northeast of the state while a trailing trough remains
draped over the state. A strong high then builds north of the
state by Monday, allowing moderate to locally strong northeast
winds to develop during the first half of next week.

A moderate, medium period north swell will continue to trend down
today, with moderate surf along north facing shores becoming small by
this afternoon. The swell continues to gradually decline on Friday as
it shifts out of the north-northeast, but experiences a small
reinforcing pulse as a strengthening low passes to the north of
the islands on Saturday. A new small to moderate long period west-
northwest swell is expected to arrive late Saturday and hold
through early next week, which will keep at least small surf along
west facing shores.

South shores will see continued moderate surf just below advisory
criteria as a long period south swell holds on today before
diminishing tonight. The next small, long period south swell will
fill in Saturday and peak Sunday, providing a small boost in surf
along south facing shores before fading into early next week. Surf
along east facing shores will remain well below average due to the
lack of trades locally and upstream through the weekend. The exception
will be for east facing shores exposed to north-northeast swells through
the weekend. Choppy surf along east facing shores looks to trend up
next week with increasing east to northeasterly winds.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from this evening through Sunday afternoon for
Oahu, Maui County, and the Big Island of Hawaii.

&&

$$

DISCUSSION...Bohlin
AVIATION...Gibbs
MARINE...Quesada