740
FXHW60 PHFO 190644
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
844 PM HST Tue Mar 18 2025

.SYNOPSIS...
A weakening upper low will slowly move northeast near the islands
over the next few days. A migratory high pressure system will
build in from the north allowing more stable trends as easterly
trade winds strengthen into the moderate to breezy range across
the region this week. Wind speeds will begin to decrease by
Saturday, becoming more variable on Sunday as another shallow cold
front approaches the state from the northwest direction. A band
of clouds and showers will move from west to east down the island
chain from Monday into Wednesday.

&&

.DISCUSSION...
The latest satellite imagery this evening shows a band of high
level cirrus clouds associated with the subtropical jet stream
moving from southwest to northeast across the island chain. An
upper level cold core low continues to produce numerous
thunderstorms along a surface wind convergence band around 100 to
200 miles west of Kauai. A few of these thunderstorms are
developing in the coastal waters south and west of Kauai this
evening. These enhanced showers and thunderstorms will likely
diminish after midnight. Elsewhere local radar imagery shows just
a few showers mainly over coastal waters and eastern island
slopes.

The latest forecast guidance continues to show a weakening low
pressure system near the islands as a migratory high center
drifts eastward across the Central Pacific basin. Higher pressure
will build in from the north as this high passes by just north of
the island chain, resulting in a transition to more stable
easterly trade winds through Wednesday, with fairly stable
moderate to breezy trade winds lasting through Saturday. Trade
wind temperature inversion heights have fallen to around 5,000 to
7,000 feet for most islands. Brief passing showers are possible
for most islands, mainly affecting windward and mountain areas in
the overnight through early morning hours. The one wrinkle in this
forecast concerns a weak wind convergence band setting up just
east of the Big Island and East Maui by Wednesday. This
convergence cloud band will move up the mountain slopes of both
islands, enhancing windward showers in these areas from Wednesday
night through Friday morning.

The high pressure ridge north of the state will begin to erode on
Saturday as a shallow cold front approaches the islands from the
northwest direction. Trade winds will diminish by Saturday night
into a more light southeast wind pattern lasting through Sunday
afternoon. The latest forecast guidance shows the shallow front
moving into Kauai and Oahu by early Monday morning with
widespread showers and north to northeast winds developing along
and behind the front as it passes through each island. A consensus
of model solutions shows the frontal cloud band moving through
the islands in Maui and Hawaii Counties from next week Tuesday
into Wednesday with enhanced shower activity forecast during this
time period, especially along north and east slopes of each island
exposed to the northeasterly trade winds.

&&

.AVIATION...
Moderate to locally breezy trades. SHRA and low cigs should favor
windward and mauka locations. MVFR conds possible in SHRA
otherwise VFR will prevail.

AIRMET Tango remains in effect for mod upper level turb downwind
of island terrain from Kauai to Maui. This will likely linger
through tomorrow.

&&

.MARINE...
Scattered thunderstorms just off the west coast of Niihau this
evening are in association with a trough located approximately
300 nautical miles west northwest of Kauai. Easterly trades will
become moderate to locally strong in magnitude as high pressure
establishes itself north northeast of the state Wednesday. A
Small Craft Advisory is in effect for these strong winds across
the typically windy waters surrounding Maui County and Big
Island through Thursday. Winds will gradually weaken Friday into
Saturday and shift southeasterly, becoming light and variable
statewide Sunday, as a front approaches the islands from the
northwest.

A series of small, medium period northwest (310-320 degree)
swells will pass through Wednesday and Friday. These swells will
hold near head-high surf along most north-facing shores and waist
to head high surf along better-exposed west shores. A significant
northwest swell originating from a storm low off the coast of
Japan may reach the islands Sunday or Monday.

East shore surf will likely pick up a bit through the middle of
the week as easterlies increase over and upstream of the state.
Many south shore surf sets will hold at average waist high as a
couple of small, long period south swells pass by this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...Walsh
MARINE...Blood