982
FXHW60 PHFO 190655
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
855 PM HST Sat May 18 2024

.SYNOPSIS...

Heavy showers and isolated thunderstorms will remain possible
over Oahu and Kauai through this evening. Expect improving trends
from east to west on Sunday. By Monday all islands will see an
improvement in weather conditions as easterly trade winds return.

&&

.DISCUSSION...

A heavy rainfall and thunderstorm threat remains for Kauai and
Oahu through tonight. A Flood Watch remains in effect for Kauai
through early morning Sunday. Latest satellite and radar shows and
area of isolated thunderstorm activity and enhanced showers
located 80 miles west of Kauai County that is steadily moving
east. This area will likely move over Kauai late tonight through
early morning Sunday, producing moderate to locally heavy
rainfall. The area may even reach portions of Oahu. Any excessive
rainfall that may develop over Oahu overnight could very easily
require a Flood Advisory given the saturated environment from
these past couple of days. Over the rest of the state, composite
radar loop shows that light showers are fairly widespread west of
the Big Island with scattered moderate showers embedded moving
from the southwest to the northeast.

High pressure will build in from east to west across the state
Sunday as the kona low shifts north and weakens. Breezy east to
southeast winds will become more light and variable over the
smaller island due to Big Island shadowing the smaller islands
Sunday. The axis of above normal moisture is expected to shift
northwest along with the associated moderate to heavy rainfall
threat. An upper level short wave trough will exit to the east.
Expect more stabilizing trends over the western half of the state.
A slight chance of thunderstorms has been added to the Big Island
afternoon forecast as this area of upper level instability shifts
east.

Easterly trade winds will return across the islands from Monday
onward. Trade wind showers may be somewhat enhanced during the
first half of next week due to lingering moisture and some upper
level instability from another short wave trough. Precipitable
water values will return to normal during the second half of the
week, supporting a more typical trade wind pattern.

&&

.AVIATION...
A trough west of Kauai will allow frequent showers to persist
through tonight, mainly for areas west of Maui. In addition,
enough instability still exists to maintain a slight chance of
thunderstorms for Kauai, Oahu, and surrounding waters. Heavier
pockets of rain will likely bring periods of MVFR
ceilings/visibility with isolated pockets of IFR ceilings and
visibility. Conditions should improve through the day on Sunday.
Expect a slight chance of diurnally driven afternoon thunderstorms
over the Big Island on Sunday.

A deep upper level trough will continue to bring areas of
moderate turbulence across the state from FL250-400 through
Sunday. AIRMET Tango is in effect across the state due to the
upper level turbulence. AIRMET Sierra in effect for mountain
obscurations over most islands except Big Island. Periods of light
to moderate rime icing is expected from Kauai to Oahu in layer
130-FL220 through tonight. AIRMET ZULU is in effect.


&&

.MARINE...
Locally strong east-southeast winds will persist through Monday,
before transitioning to easterly trades Tuesday through late next
week. A Small Craft Advisory remains in effect through Sunday for
the windier waters around Maui County and the Big Island.

The current south swell will slowly lower tonight and Sunday,
while a new long-period south swell fills in. This will keep south
shore surf near low end advisory levels through Sunday. The swell
will hold Sunday night and Monday, then gradually lower through
the middle of next week. South shore surf will fall back below the
summertime average Thursday through next weekend, with only small
south and south-southwest swells rolling through.

The current small northwest swell will gradually lower tonight
through Monday, with north shore surf going flat Tuesday through
next weekend.

Surf along east facing shores will remain well below average
through early next week. An upward trend is expected Tuesday
through late next week as trade winds strengthen over and
upstream of the islands.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 6 AM HST Sunday for Niihau-Kauai-

High Surf Advisory until 6 PM HST Sunday for all south facing
shores.

Small Craft Advisory until 6 PM HST Sunday for Maui County
Windward Waters-Alenuihaha Channel-Big Island Windward Waters-
Big Island Leeward Waters.


&&

$$


DISCUSSION...Almanza
AVIATION...Thomas
MARINE...Jelsema