835
FXHW60 PHFO 181403
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
403 AM HST Sat May 18 2024

.SYNOPSIS...

A kona low northwest of the state will continue drawing unstable
tropical moisture northward over Kauai County through today. The
kona low will begin slowly drift north and weaken over the next
few days improving trends spreading from east to west, though
enhanced rainfall may linger over Kauai and Niihau through tonight.
By Monday all islands will see an improvement in weather
conditions as easterly trade winds return.

&&

.DISCUSSION...

A kona low remains centered roughly 850 miles northwest of Kauai
with a trough orientated northeast to southwest 150 miles west of
Kauai. Radar and satellite imagery shows isolated thunderstorms
embedded along the main line of convergence just east of the
trough. Radar is now showing this main line of convergence nearing Kauai
County from the west early this morning. The Flood Watch for
Kauai remains in effect through tonight as current observations
remains in line with hi- res model guidance showing rainfall
activity picking up this morning. Although most showers will
remain light to moderate a few heavy showers and isolated
thunderstorms could still develop as the day progress, in
addition to this band lingering over Kauai County during the most
of the day. A few stray showers could also reach as far as Oahu
today so have increased the pops slightly especially for the
leeward and interior areas this morning.

A ridge of high pressure will slowly build in from east to west
across the state today and Sunday as the kona shifts north and
weakens. East southeast winds will keep winds light an variable
along sheltered leeward locations down stream of the Big Island.
This pattern could also be conducive for showers to develop along
the Koolau range this afternoon and evening. Upper levels
continue to show divergence aloft that will keep some instability
over western end today. Expect more stabilizing trends with
decreasing showers as east to southeast winds spread across the
state. Likely by Sunday, the moderate to heavy rainfall threat
will diminish over Kauai as more stable conditions fill in across
the state.

Easterly trade winds will return across the state from Monday
onward. Trade showers may be somewhat enhanced during the first
half of next week due to lingering moisture and some upper level
instability from a short wave trough during the first half of next
week. The tongue of high precipitable water vapor should become
more normal during the second half of next week allowing for a
more typical trade wind pattern.


&&

.AVIATION...
An unstable tropical environment with a low level trough over
Kauai will keep MVFR conditions with brief IFR conditions possible
in moderate to locally heavy showers through tonight. Lingering
instability near Oahu will keep periods of MVFR conditions in
showers. Moderate turbulence may develop later this morning over
all islands from FL280-400.

Most islands will see light large scale southeast to south winds
interacting with overnight land and daytime sea breezes through
the weekend. Clouds and showers will build over island mountain
and interior sections during the day with some clearing at night
for most islands. Kauai will be the exception to this rule as a
low level trough will approach the island enhancing clouds and
showers through tonight.

AIRMET Sierra in effect for mountain obscurations over all islands.

Occasional light rime icing is expected from Kauai to Oahu in
layer 140-FL250.


&&

.MARINE...
Moderate to locally strong east to southeast winds associated
with a kona low far north-northwest of the state will persist
over the weekend. A shift out of a more typical easterly trade
wind direction is expected early next week as it lifts northward
and away from the region and the ridge builds to the north. A
Small Craft Advisory is now in effect for the windier coastal
waters around Maui County and the Big Island through Sunday.

Surf along south facing shores will remain up through early next
week due to overlapping, long-period south-southwest swells. The
first swell will hold around the advisory level today before
briefly lowering Sunday. Offshore buoy observations are holding
strong with the peak energy associated with this swell now into
the 14-16 second bands. The short-period wind chop added from the
southerly winds will linger today, then ease as we transition back
to an east to southeast wind regime by early next week. A fresh,
long-period south-southwest swell will fill in through the day
Sunday, then peak slightly lower than the current swell early next
week before easing Tuesday through midweek.

Surf along north facing shores will steadily lower through the
weekend, with a return to a more typical pattern for this time of
year next week.

Surf along east facing shores will remain well below average
through the weekend. An upward trend is possible next week as the
trades return locally and far upstream over the eastern Pacific.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for Niihau-Kauai-

High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai
South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Southeast-
Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central
Valley South-South Maui/Upcountry-South Haleakala-Big Island
South-Big Island Southeast.

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...Bohlin
MARINE...Gibbs