650
FXHW60 PHFO 110700
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
900 PM HST Fri May 10 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 through Saturday. Weather
conditions around this upper low will support some of these
developing thunderstorms in the strong to severe range. Heavy
rain 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
threats. However this wet weather pattern may continue through the
week as another low pressure system approaches from the north
possibly producing southerly kona winds over the western islands
by Wednesday.

&&

.DISCUSSION...
The satellite water vapor imagery this evening shows a cold core
upper low over Oahu drifting slowly eastward. This rather large
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 range. The main
threats with this system will be flooding, and strong gusty
winds near thunderstorm. A Flood Watch remains in effect through
Saturday morning statewide. This Flood Watch may be extended for
some islands through Saturday evening with the morning forecast
package.

In the short term, global model guidance shows the low pressure
system pivoting over Oahu on Saturday before slowly weakening and
drifting northeastward away from the islands. 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 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 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 will depend highly 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
forecast. Stay tuned for changes to the long range 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 tonight. Shower activity will remain greatest over areas
east of Molokai, with periods of MVFR and local IFR expected.
Thunderstorms will continue near Maui and the Big Island tonight,
but activity should wane late tonight into Saturday morning. Light
winds should allow for sea breeze development Saturday afternoon,
with scattered showers possible over the interior and sheltered
leeward areas.

AIRMET Sierra for tempo mountain obscuration remains in effect for
areas east of Oahu, but given the latest trends will likely be
able to cancel the AIRMET over the smaller islands with the next
scheduled issuance.

AIRMET Tango may be necessary for moderate mid to upper level
turbulence as the backside of 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 Saturday
morning 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 through Saturday. Additionally, as a surface
trough in the Kauai Channel strengthens and moves across the
island chain, light and variable winds will prevail across local
waters, except for 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 into the
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 is
building in this evening. This swell will increase north and west
shore surf through Saturday morning, then decline later Saturday
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 until 6 AM HST Saturday for all Hawaiian Islands.

High Wind Warning until 6 AM HST Saturday for Big Island Summits.

Winter Storm Warning until 6 AM HST Saturday for Big Island
Summits.

&&

$$

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