224
FXHW60 PHFO 180658
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
858 PM HST Fri May 17 2024

.SYNOPSIS...

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


&&

.DISCUSSION...

A kona low remains centered roughly 750 nm northwest of Kauai and
a trough orientated northeast to southwest near Kauai. Latest
satellite imagery shows a broad broken cloud band extending from the
northeast to southeast over Kauai and Oahu and some mid- level
and high clouds streaming from west to east over the rest of the
island chain. Radar imagery earlier this evening showed the
rainband that brought significant rainfall to Oahu Thursday and
earlier this morning has quickly moved north of Kauai with some
rainfall gauges picking up over a quarter of an inch an hour.
Currently radar imagery shows rainfall activity has quited down
with scattered moderate to light showers building along the Koolau
range this evening and moving from the south to north near Kauai.

The Flood Watch for Kauai County remains in effect through
Saturday night as hi-res models continue to show a possibility for
heavy rainfall to build back east over Kauai Saturday morning.
The main consideration for the island of Kauai continues to be how
long the band lingers over the island before moving off to the
northwest as the kona low exits the region. While consensus is
that conditions will begin to improve Saturday night, the flooding
concerns could linger a bit longer should this be a slower
transition. Models also are still hinting that one last moisture
surge back towards Oahu is possible on Saturday night, but
confidence remains low in this occurring at this time.

High pressure will slowly build into the region this weekend as
the kona low exits the pattern to the north. 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.

More typical easterly trade winds will return across the state from
Monday onward with only brief passing showers in the forecast
favoring the typical windward and mountain areas through the
middle of next week.


&&

.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 lasting into Saturday.
Lingering instability near Oahu will keep periods of MVFR
conditions in showers favoring the eastern slopes. Most islands
will see light large scale southeast to south winds interacting with
overnight land and daytime sea breezes over each island 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 enhance clouds and showers for the next 24
hours.

AIRMET Sierra in effect for mountain obscurations over Kauai,
Oahu, and the eastern slopes of the Big Island.

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


&&

.MARINE...
Fresh to locally strong south to southeast winds associated with
a kona low north-northwest of the state will persist into Saturday.
A shift out of the east to southeast direction is expected over
the weekend through early next week as it lifts northward and away
from the area and the ridge begins to build north of the area. A
Small Craft Advisory remains in effect for the Windward and
Leeward Big Island waters (Hamakua Coast and waters near South
Point) through early Saturday. As we trend back to a more typical
trade wind pattern by the end of the weekend, a SCA may be needed
for the windier locations around Maui County and the Big Island.

Surf along south facing shores will remain up through early next
week due to overlapping, long-period south-southwest swells. The
first swell that peaked today will hold around the advisory level
into Saturday before briefly lowering. The short-period wind chop
added from the southerly winds will linger into Saturday, then
ease as we transition back to an east to southeast wind regime by
Sunday. This will translate to cleaner surf conditions. 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 Saturday night for Niihau-Kauai-

High Surf Advisory until 6 PM HST Saturday 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 AM HST Saturday for Big Island
Windward Waters-Big Island Leeward Waters.


&&

$$


DISCUSSION...Almanza
AVIATION...Bohlin
MARINE...Jelsema