Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 04/13/2026 04:38:00 AM UTC

                        
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FXHW60 PHFO 121838
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
838 AM HST Sun Apr 12 2026

.SYNOPSIS...
Showers will continue for the entire day over Kauai and Oahu with
the heaviest rain and greatest flooding potential over Oahu. LIght
trades return at the end of the week.


&&

.SHORT TERM UPDATE...
Issued at 834 AM HST Sun Apr 12 2026

Limited instability on this mornings Lihue sounding indicative of
the very warm, saturated, and poor lapse rate environment in place
over the islands. Radar imagery matches forecast expectations well
with decaying rainfall over Kauai and developing showers poised to
spread across Oahu and possibly Molokai this morning. As expected,
guidance still indicates low-level convergence draped over Oahu for
much of the day. This is related to the deep tropospheric frontal
structure tied to strengthening right entrance jet dynamics aloft.
However, this has yet to bear out on radar with no discernible
organization evident so far. Instead, the rain shield is broad and
stratiform in nature with convective elements that so far are
struggling to produce even 1" per hour. Given that Oahu is lined up
to receive about 15-18 hours of nearly uninterrupted rainfall, rain
rates are the only thing standing between routine flood impacts and
a much more serious flash flooding situation. However, at this time
there does not appear to be any reason to expect rates to increase
as instability is essentially nil and forcing does not change in
type or magnitude at any point. Perhaps low-level convergence
materializes and supports a period of higher rates or
localized/brief 1-2"/hr rates within transient convective cells
advance over the island, but as of this morning this event appears
to be a 0.5"/hr low rate grinder with several inches of rain spread
over many hours. Of note, the Flood Watch remains in effect for
the Big Island to cover convective potential mainly over the South
Kohala and North Kona Districts this afternoon.

&&

.AVIATION...
Issued at 834 AM HST Sun Apr 12 2026

An unstable band of deep tropical moisture will move up from the
south under an upper level disturbance. Weather conditions will
destabilize today, producing widespread MVFR and isolated IFR
conditions statewide with low clouds, showers and isolated
thunderstorms from early this morning through early Monday
morning. Oahu is expected to be the most likely to receive
periodic heavy showers. Light land-sea breezes less than 10 kts will
prevail across all sites.

AIRMET Sierra remains in effect for mountain obscuration above
1500 ft for Kauai and Oahu, as well as for IFR conditions at
Molokai, Lanai, and Maui. These conditions are expected to remain
today with the oncoming shower threat, with some relief expected
later this evening as conditions dry out, however low clouds may
remain due to light winds and lingering moisture.

Widespread cloud cover over the state today may also lead to
moderate icing.


&&

.MARINE...
A surface trough will linger in the vicinity of the central
islands into early next week, keeping moderate to fresh
southeasterly winds to its east, and light and variable winds to
its west. This weak surface boundary along with an upper level
disturbance moving into the region brings another round of showers
and isolated thunderstorms today into Monday. As the surface
trough lifts north and high pressure to the northeast begins to
takes over at the surface, gentle to moderate easterly trades will
gradually develop across the Hawaiian coastal waters by the end
of next week.

A moderate, short to medium-period north-northwest swell (340
degrees) generated by the formerly-gale force low north-northwest
of the main Hawaiian islands arrives along north and west facing
shores today. This will maintain small to moderate surf through
the beginning of the week, followed by a decline in northwest
swell energy for the rest of the week.

A medium-period south swell will continue to decline through Monday.
By Tuesday, however, a new south swell will arrive, once again
providing a boost to surf along south facing shores through mid week
before gradually subsiding into the weekend.

Surf along east facing shores remains below seasonal average with
lighter than average trade winds near and upstream of the islands
forecast through next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Monday afternoon for Hawaii.


&&

$$

SHORT TERM UPDATE...JVC
DISCUSSION...Pierce
AVIATION...Evans
MARINE...Quesada