Honolulu, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

551
FXHW60 PHFO 191909
AFDHFO

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

.SYNOPSIS...
A kona low will bring several rounds of moderate to heavy rainfall
to the islands through the weekend resulting a risk of flash
flooding.

&&

.SHORT TERM UPDATE...
Issued at 907 AM HST Thu Mar 19 2026

Large scale environment generally remains weakly subsident this
morning beneath subtle mid-level height rises and downward motion
within a healthy right exit region of the upper jet. The low and mid-
levels are nevertheless largely saturated courtesy of moisture left
behind by the previous system, and a PWAT of 1.75" on this morning`s
Lihue sounding is largely representative of moisture confined to the
lowest 25kft. A relatively deep layer of southwest flow has
developed ahead of the nascent kona low which resides a few hundred
miles west of Kauai at press time. Weak isentropic ascent within
this corridor of SW flow is supporting a wide coverage of stratiform
over the state this morning, particularly over Kauai and SW portions
of the Big Island. The batch over the Big Island will likely be
transient in nature, advancing over the S/SE slopes through today
while the area of rainfall over & upstream of Kauai will have more
staying power courtesy of upstream westerlies in the 850-700mb layer
and attendant convergence aloft. Finally, weak convergence within SE
flow in the boundary layer is supporting an increasing coverage of
shallow convection upstream of Kauai. Radar observations suggest
rain rates in excess of 1.0"/hr within these showers nad may pose a
low-end nuisance flood threat for Kauai today. These showers may be
aided by a very subtle shortwave embedded in the flow about 300
miles W of Kauai. Showers may therefore tend to develop eastward
through the day eventually training over Oahu and posing a similar
nuisance flood type of threat prior to the start time of the Flood
Watch.

A wet night is in store for Oahu and Maui County as forcing
gradually spreads eastward allowing rainfall intensity to increase
as it shifts from Kauai toward the central portion of the state.
Uncertainty increases by late tonight as the global models develop a
secondary area of low pressure north of Kauai that appears to be
mostly tied to convective feedback. While not entirely unrealistic,
preference lies with something closer to the UKMet which allows a
stronger surface low to develop as surface pressure falls remain
tied to the strongest large scale forcing. The degree to which the
models deepen the convectively-enhanced secondary low is the
difference between The EC`s eastward solution, the UKMet which is
further west, and the GFS which lies in between. Given the solution
preference and the slight westward trend noted in the GFS and UK,
Kauai will be added to the Flood Watch with this morning`s update.

&&

.PREV 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...
Issued at 907 AM HST Thu Mar 19 2026
Light to moderate southeast winds will strengthen tonight as
surface low pressure west of the islands and an associated trough
stretching north of the state deepen. Moderate to locally fresh
south to southwest winds will prevail Friday and Saturday, and
periods of heavy showers and thunderstorms are expected. The low
will lift to the north of the state on Sunday, likely allowing
moderate northerly winds and lower chances for rainfall to
develop around Kauai. On Monday, high pressure building north of
the state will push a surface trough eastward over the islands.
Fresh to strong northeast winds will require a Small Craft
Advisory (SCA) over much of the island chain, though variable
winds could linger around the Big Island through the day.

A moderate, medium period north-northwest swell will continue to
trend down today, then shift out of the north-northeast Friday. A
moderate reinforcing north-northeast swell is expected Saturday
and Sunday, followed by a potentially larger pulse of north-
northeast swell early next week that could produce surf near the
High Surf Advisory level. A small, overlapping west-northwest
swell is expected to arrive late Saturday and hold through early
next week.

South shores will see continued surf just below advisory criteria
as a long period south swell holds on today. The swell will
diminish tonight and Friday, followed by a small south-southwest
swell this weekend. Aside from areas exposed to wrapping north
swell, surf along east facing shores will remain well below
average. As northeast trade winds develop early next week, rough
surf will return to east facing shores.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 6 PM HST this evening through Sunday afternoon
for Hawaii.


&&

$$

SHORT TERM UPDATE...JVC
DISCUSSION...Bohlin
AVIATION...Gibbs
MARINE...Wroe