217
FXHW60 PHFO 200705
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
900 PM HST Sat Apr 19 2025

.SYNOPSIS...
Trades have returned but will occasionally become weak enough to
allow localized land and sea breezes to be the dominant wind.
Moderate trades around the islands will continue through Monday,
as thicker clouds and greater shower frequency favors windward
exposures and mauka slopes. A storm low will drop down northwest
of the state through the middle of next week. This will again
disrupt trade flow and introduce higher chances for island-wide
rain and potential storms.


&&

.DISCUSSION...
Widely scattered showers pepper the islands this evening with the
greatest concentration of rain within downstream island plumes.
While moderate trades have returned to the islands, more sheltered
leeward locations exhibited weak enough winds to allow afternoon
warming to initiate and blossom deeper cumulus. These clouds
quickly produced an inch of rain (or slightly more) over such
areas as southern upcountry Maui in the Kula area between Kihei
and Keokea. Greater than inch amounts also occurred today around
the Puu Mali peak outside of Waimea on north Big Island just
south of the Kohala Mountains. Elsewhere, most windward communities
picked up a few drops but most of the day remained dry as the
majority of the shower activity remained offshore. A large surface
high centered far northeast of the state will continue to create
a tight enough downstream pressure gradient to produce a couple
of days of moderate trades. The islands still lie within a diffuse
upper level trough that will eventually wash out to the northeast
by Monday morning. The regional atmosphere still remains
marginally unstable and moist enough to support widely scattered
showers both Easter Sunday and Monday. More organized cells will
occasionally hang together across the higher terrain and make it
into leeward areas. There still remains an outside chance of
localized flooding into tomorrow from cells that stubbornly root
themselves over more windward-facing (typically mauka) slopes.
Generally, the island weather forecast calls for very similar
weather as experienced today.

The next weather maker will come in the form of a closed-off upper
low that will sink down along and near 170W longitude and come
within 600 miles northwest of Kauai. The west northwest positioning
of this low will pull up more moisture-rich air over the state from
the southwest. As heights begin to lower and mid to upper layers
cool from the west, enhanced instability within this moistened air
mass will likely induce another round or three of widespread showers
and thunderstorms. With the approach of either a broad open wave
trough or a closed low northwest of the islands next week, the
highest rain probabilities (or areas to receive more frequent rain
episodes) will be across the western half of the state. Flooding
concerns may be re-awakened next Tuesday through Thursday as locally
heavy precipitation falls upon saturated soils.


&&

.AVIATION...
Moderate trades have returned and will persist through tomorrow,
ushering clouds and showers into windward and mauka areas. However,
winds will be light enough to support isolated sea/land breeze
development that will bring additional clouds and showers to some
leeward and interior areas during the afternoon hours and clearing
of these areas overnight. MVFR conditions will be possible in any
showers, otherwise VFR conditions should prevail.

No AIRMETs are currently in effect.


&&

.MARINE...
Gentle to moderate trades will continue through Monday, then veer
southeasterly in advance of a deep low that will develop NW of
the islands. Winds further veer southerly Tuesday into Wednesday and
then hold steady where they will remain for the remainder of the
week. There will be a chance of thunderstorms during this time,
particularly over the western waters.

A moderate, medium period N swell will gradually trend down
through Sunday producing below average surf along N facing
shores. A tiny, long period NW swell will fill in Monday into
Tuesday before subsiding Wednesday which will prevent surf from
going flat. In the long range, guidance depicts a gale forming
Monday near the Kurils then tracking northeast to the western
Aleutians by Wednesday. In this scenario, Hawaii would experience
an uptick in the NW swell next weekend.

Surf along E facing shores will remain small through the weekend.
E shore surf could become tiny by mid week as southerly winds
emerge.

A tiny, long period S swell will move through this weekend
providing a small boost in surf along S facing shores. A larger,
long period SSW swell will fill in Monday into Tuesday and produce
near to above average surf along S facing shores by mid week before
slowly subsiding through the rest of next week.



&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Blood
AVIATION...Walsh
MARINE...Almanza