805
FXHW60 PHFO 041336
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
336 AM HST Sat May 4 2024

.SYNOPSIS...
Breezy trade winds will continue into Monday as a high pressure
system remains anchored far north of the state. An upper level
low northwest of Kauai will slowly drift across the island chain
through Monday enhancing shower activity mainly over windward and
mountain areas of each island. By Tuesday the disturbance aloft
weakens and drifts northeast of the state, briefly decreasing
shower activity. A low level cloud band will ride into the islands
on the trade winds with support from an upper level trough from
Wednesday to Thursday, increasing shower trends over all islands.

&&

.DISCUSSION...
Satellite imagery water vapor channel continues to show an upper
level low roughly 700 miles to the west-northwest of Kauai this
morning. An upper level trough is also evident over the islands
enhancing trade wind showers as shown on island radar. The
subtropical jet stream flows from west to east over the Big Island
this morning, and this jet stream will slowly drift north over
the next few days.

A 1030 mb high pressure center and subtropical ridge will remain
anchored over the Central Pacific basin, far north of the Hawaiian
islands through the weekend. This system will produce breezy
easterly trade winds across the Hawaii region into Monday. Trade
wind speeds will slowly decrease to moderate levels from Monday
into Tuesday as the high pressure center drifts eastward away from
the island chain and a long wave trough moves into the Central
Pacific. Easterly trade winds will continue to blow at moderate
levels through Friday.

Expect continued enhanced showers across the state as the unstable
upper level disturbance slowly drifts eastward across the island
chain. Most of the rainfall amounts will favor windward and
mountain areas as breezy trade winds build clouds up and over the
windward mountain slopes. Down sloping trade wind flow over the
leeward sides of island mountain ranges will tend to decrease
shower activity for leeward areas of each island. Shower trends
will tend to increase during our typical diurnal rainfall maximum
in the overnight to early morning hours.

In the extended forecast we continue to see a long band of
unsettled shallow clouds, remnants of an old Eastern Pacific cold
front, drifts into the islands on the moderate trade winds from
Wednesday morning into Thursday. This cloud band may produce wet
weather over all islands for an 18 to 24 hour time period. The
highest rainfall amounts will tend to favor windward and mountain
areas, however many leeward sites may also see measurable
rainfall totals with this next system. This fairly shallow cloud
band will likely not be deep enough to produce heavy rainfall,
rather more beneficial rain is forecast for all islands.

&&

.AVIATION...
Breezy easterly trade winds will persist through the weekend,
with clouds and showers favoring windward and mauka locations.
MVFR CIGs/VSBYs in showers are possible over windward areas,
especially overnight through the early morning periods. Elsewhere,
VFR conditions will prevail with an occasional shower making it
to leeward sections of the smaller islands.

AIRMET Sierra is in effect for tempo mountain obscuration for
windward portions of each island. This may persist through the
early morning hours before conditions improve.

AIRMET Tango is in effect for mod turb below 9000 feet downwind
of island terrain, which will continue through the weekend.

&&

.MARINE...
Consolidating high pressure far N of the islands will support
strong E trade winds into Monday, with island terrain accelerating
winds to near-gale force in the windier channels. The high will
move E thereafter, leading to a gradual easing in trade wind
speeds by the middle of next week. A Small Craft Advisory (SCA)
for all waters will remain posted through at least Sunday. A
disturbance aloft will allow for the development of a few heavier
showers the next couple of days, producing periods of gusty winds
and reduced visibility.

Combined seas increased to near 10 feet at several of the near-
shore PacIOOS buoys overnight, mostly due to an increase in short-
period wind waves. These wind waves arriving along E facing
shores will result in rough and choppy surf for at least the next
several days. Also, a new medium- to long-period NNW swell will
peak near 4 feet today. This swell will gradually diminish
Sunday, but another relatively small, moderate-period NW swell is
expected Monday and Tuesday.

Elsewhere, the storm track in the S hemisphere recently became
favorable for the generation of Hawaii-bound S swell, with pulses
of swell arriving on-and-off for at least the next week. The
first of these long-period S swells is expected to arrive later
this weekend and early next week, with peak surf heights remaining
below High Surf Advisory (HSA) heights, although later swells may
be large enough to warrant a HSA.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Monday for all Hawaiian
waters-

&&

$$

DISCUSSION...Bohlin
AVIATION...Gibbs
MARINE...Birchard