850
FXHW60 PHFO 111338
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
338 AM HST Sat May 11 2024

.SYNOPSIS...
An unstable upper low slowly drifting eastward through the islands
will continue to produce periods of heavy rain and thunderstorms
with elevated flood threats statewide today. Weather conditions
around this upper low will support some of these thunderstorm
intensities becoming strong to severe. Heavy rain, flooding, frequent
lightning and strong gusty winds will be the primary threats. By
Monday the upper low weakens and lifts towards the northeast away
from the island chain, decreasing the thunderstorm and heavy rain
activity. However this wet weather pattern will likely continue
through the week as another stronger low pressure system
approaches from the north, possibly producing southerly kona winds
over the western islands by Wednesday.

&&

.DISCUSSION...
The satellite water vapor channel imagery this morning continues
to show an unstable cold core upper low over Maui County drifting
slowly eastward. The orientation of this low will pivot over the
islands as a secondary pulse of energy moves into Kauai and Oahu
today extending the threat for heavy rain and thunderstorms over
the western islands. This rather large and unstable upper low will
produce periods of heavy rainfall and thunderstorms across the
state into Sunday. Some of these thunderstorms will grow into the
strong to severe intensity range. The main threats with this
system will be heavy rain, flooding, frequent lightning, and
strong gusty winds near thunderstorms. The Flood Watch was
extended for all islands through this evening. This watch may
decrease in coverage for the western islands by tonight.

In the short term, global model guidance shows the upper low
pivoting over the islands today before slowly weakening and
drifting northeastward away from the state. Enough instability
and vertical wind shear will produce periods of isolated to
scattered thunderstorms across the state. Some of these storms
will become strong to severe in intensity with strong gusty winds,
hail, and the potential for water spouts. Flash flooding, strong
gusty winds and frequent lightning will develop quickly in this
weather pattern and for these reasons outdoor activities this
weekend should be postponed if possible.

Monday through Tuesday...Heavy rain and thunderstorm threats
diminish by Monday as the low weakens and slowly drifts
northeastward away from the state. Weak upper level troughing
however will keep wet weather in the forecast with southeasterly
winds over the islands through Tuesday.

Wednesday through Friday...Another unseasonably strong low will
approach the islands from the north on Wednesday. A surface low
forming under the upper low will be stronger than the previous
system and may produce southerly kona winds over the western half
of the state. The latest forecast guidance shows the surface low
center will setup roughly 400 to 600 miles west-northwest of
Kauai. This unstable southerly kona wind flow may bring another
round of heavy rain and thunderstorms favoring the western islands
of Niihau, Kauai and Oahu from Wednesday through Friday. In the
latest model solutions Kauai County will be under the highest
threat for flooding, thunderstorms, and strong gusty winds during
this time period. This portion of the long range weather forecast
will likely change over time. Much of these severe weather impacts
are highly dependent upon the location of this low pressure
system relative to each island. Small changes to the location of
the low center will make large changes to the island forecast.
Stay tuned for changes to the long range local weather forecast,
as the time period grows shorter, and island by island weather
impacts evolve.

&&

.AVIATION...
A strong upper level disturbance will continue to move across the
state today. Enhanced shower activity and isolated to scattered
thunderstorms will produce periods of MVFR and local IFR. Light
winds should allow for sea breeze development this afternoon, with
scattered showers possible over the interior and sheltered
leeward areas.

AIRMET Sierra for tempo mountain obscuration remains in effect for
the Big Island this morning. It may become necessary to include
the smaller islands later today as shower activity increases.

AIRMET Tango for moderate to isolated severe mid to upper level
turbulence remains in effect as the upper level disturbance moves
across the state.

AMD NOT SKED for PMDY continues due to equipment issues, with no
timeline for restoration.

&&

.MARINE...
Strong to severe thunderstorms are possible through today as an
unusually strong upper level disturbance moves across the area.
These thunderstorms have the potential to produce strong wind
gusts, hail, and frequent lightning. Marine interests should
continue to monitor for Special Marine Warnings that may be
issued. Light and variable winds will prevail across local waters,
except within and near thunderstorms. Light to moderate easterly
trade winds will begin building back into the region on on Sunday.

A long-lived south swell will affect the islands this weekend.
Although the swell will persist for the next several days, surf
should continue to trend down as the period declines. Another
series of overlapping, long-period south swells will give another
sizable boost to south shore surf Wednesday through late next
week.

A small, reinforcing short-period north-northwest swell will
increase north and west shore surf through this morning, then
decline later today into Sunday. A new small, long-period
northwest swell will build Sunday night, giving north shore surf a
boost early next week. Surf along east facing shores will be well
below normal levels through the middle of next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for all Hawaiian Islands.

Wind Advisory until 6 PM HST this evening for Big Island Summits.

Winter Weather Advisory until 6 PM HST this evening for Big
Island Summits.

&&

$$

DISCUSSION...Bohlin
AVIATION...Ahue
MARINE...Powell