Waimea, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

680
FXHW60 PHFO 120111
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
311 PM HST Sat Apr 11 2026

.SYNOPSIS...
Showers and isolated thunderstorms will spread over the western
half of the state tonight and become heavy over central portions
of the state Sunday into Sunday night. Flash flooding is possible.
The heaviest rain is currently anticipated over Oahu and Molokai,
and possibly Kauai.

&&

.DISCUSSION...

Visible satellite indicates abundant high clouds that have limited
surface heating and kept interior convection in check over island
interiors. Low level clouds indicate persistent troughing draped
over Maui County. This boundary supported scattered light showers
this morning, but those have dissipated with diurnal warming.
About 500 miles southwest of Kauai an extensive band of showers
and thunderstorms is seen lifting northeastward toward the island.
This activity is maintained by rather weak convergence and
abundant tropical moisture characterized by PWAT values around
2.25". This moisture rich environment is in the process of
returning to the islands where sea level dewpoints are already
hovering in the low to mid 70s over Oahu and Maui County. This
activity is estimated to reach the western end of the state around
midnight.

Upper troughing approaches from the west tonight supporting additional
pressure falls and strengthening of low-level convergence further
east than the aforementioned band of showers upstream of Kauai.
Further supporting this idea is a slight eastward shift by the 18z
guidance with respect to the heavy rain axis. This is perhaps
partly due to existing surface troughing drifting further east
than anticipated. As right entrance forcing ramps up tonight into
Sunday, model cross sections are actually impressive with how
quickly a deep, convergent frontal structure redevelops over
central Hawaii. The front is shown to extend from the surface and
tilt northwestward with height until it reaches jet level west of
the state. An appreciable frontal circulation is also shown to
accompany this developing feature and increases confidence in the
idea of development and maintenance of a weak-to-moderately
forced axis of heavy rain. Primary forecast uncertainty lies with
the position of this heavy rain axis. Although surface troughing
has drifted eastward and settled over Maui County this afternoon,
suspect convergence will tend to reorganize slightly further west
as larger scale forcing manifests. Strong surface-700mb convergence
then establishes over or in the vicinity of Oahu and slowly
drifts westward with time.

Several inches of rain is likely over Oahu, and potentially part
or all of Molokai. From a forecast accuracy standpoint, there is
some concern that the heavy rain band could hang up in the Kaiwi
Channel between Oahu and Molokai, but the expectation for a slow
westward drift suggests Oahu will ultimately receive several
hours of heavy rainfall one way or another. The heavy rain band
potentially reaches Kauai on Sunday night, but that remains quite
uncertain at this juncture. On the other hand, confidence is
increasing that the Big Island will remain largely dry save for
typical afternoon showers over upslope areas.

Given the flood response that was observed yesterday, there is
concern for significant flash flooding impacts on Sunday
especially since yesterday`s rainfall further saturated the
ground.

The existing Flood Watch is "considerable" and that is
where it will stay with this forecast issuance. Overnight shift
will determine the necessity of continuing the Flood Watch for the
Big Island, but will leave in place for now.


&&

.AVIATION...

A light seabreeze pattern prevails today over the western half of
the state, while moderate S-SE winds occur over the eastern half
of the state. Expect winds to trend lighter statewide, as a narrow
band of moisture forms over the central portions of the island
chain overnight, and potentially last through Monday morning. VFR
to MVFR conditions are likely prior to the formation of the
moisture band, and MVFR to isolated IFR conditions are expected to
occur within showers once the moisture band forms. Oahu has the
highest likelihood of receiving impacts, but shower coverage could
reach Kauai and Maui county.

AIRMET Sierra is in effect for mountain obscuration above 1500 ft
for Molokai, and windward Oahu. It is also in effect for IFR
conditions on Lanai. Lanai will likely continue to see IFR
conditions due to lingering showers and low ceilings. Mountain
obscuration coverage will likely be expanded overnight as showers
develop.

Icing threat is diminished for now, but light icing may be
possible tomorrow as high clouds fill in over the state.

&&

.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 may help to bring another
round of showers and isolated thunderstorms tonight through
Sunday. 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 medium-period south swell will gradually 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.

A moderate, short to medium-period northwest swell generated by the
gale force low to the northwest filled in early this morning and
is providing small to moderate surf to north and west facing
shores this afternoon. Another northwest reinforcement will arrive
on Sunday and maintain small to moderate surf through the
weekend, followed by a decline in northwest swell energy next
week.

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 all Hawaii islands-


&&

$$


DISCUSSION...JVC
AVIATION...DT
MARINE...Farris