717
FXHW60 PHFO 211905
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
905 AM HST Tue Jul 21 2026

Moderate to breezy trades deliver showers windward and mauka into
next week. Shower coverage will be highest today followed by a
drying trend.

&&

.SHORT TERM UPDATE...

Despite a deep layer of dry mid-level air beneath the resident
subtropical ridge, PWATs checked in at 1.49" in Lihue and 1.72" in
Hilo this morning. This is a testament to rich boundary layer
moisture that also has sea level dewpoints hovering around a muggy
70F. The morning Hilo sounding also showed light to moderate SE flow
through the depth this layer which will delay its exit westward as
moisture slowly advances NW roughly parallel to the island chain.
Widespread showers this morning, particularly windward and mauka,
will likely persist to some degree through the diurnal heating
period before filling in again tonight. By Wednesday morning,
boundary layer flow is more uniformly westerly and trades become
breezy in response to the governing high over the NE Pac building
slightly southward. This will usher this batch of moisture and
attendant showers westward during Wednesday and set the stage for a
return to high stability and a drier trade wind pattern by Thursday
as 500mb heights build to 591dm and PWATs gradually decline to
around 1 inch. A weakening TC Fausto then enters the picture early
next week with guidance generally tracking the system near or north
of the islands during the mid-week period.

&&

.PREV DISCUSSION...
Issued at 345 AM HST Tue Jul 21 2026
Early morning satellite imagery is depicting better organized
areas of thick clouds surrounding the island chain. This is in
association with a moist air mass lingering over the islands.
Veering winds within a deeper, moistened boundary layer will
yield the potential for areawide rain through tomorrow.
Precipitation has filled in across the state since midnight with
the majority of the smaller islands picking up a couple of tenths
to about a half an inch of rain, with localized greater than one
inch amounts, the past six hours. The quick pace and widely
scattered nature of these cells should keep any localized flooding
concerns at bay. Heavier, more intense pockets of rain may cause
nuisance low lying area flooding and street ponding today and
tomorrow.

This noticeable boost in statewide shower activity will likely
hang with us into Wednesday afternoon as this batch of higher low
to mid layer moisture lingers over the region. Typically drier
leeward communities may experience more frequent showers such as
enhanced shower coverage over lee Oahu in response to east
southeast wind convergence downstream of Maui County. After a
couple of days of weaker winds, trades will become more fresh as
northeastern Pacific surface high pressure building south tightens
the gradient across the area. Drier air filling in behind this
west-exiting moist air mass late Wednesday will ensure a drier
end of the week. Breezy trades, higher stability and limited
showers focused windward and upslope mauka will be the day-to-day
theme at week`s close.

Although decent northerly shear continues to impact Hurricane
Fausto, currently located about 650 nm off Cabo San Lucas, BCS,
he is slowly intensifying. NHC is forecasting Fausto to continue
on a slow and steady west to slight northwest track through Thursday.
A pick up in speed is expected with the majority of the numerical
model guidance keeping the storm just south of 20N into Saturday
as it nears 140W. If Hurricane Fausto stays on this west northwesterly
track, localized trade flow will be interrupted as the cyclone
passes northeast of the state early to mid next week.

&&

.AVIATION...
Radar and satellite imagery depict showers OVER most windward
sites with scattered showers making it to leeward sites. This will
continue through the day, tapering off from east to west
overnight. Moderate trades will continue.

AIRMET Sierra is in effect for the windward side of most islands
due to ongoing shower activity. This is expected to continue until
at least the early evening hours, and should clear from east to
west overnight.


&&

.MARINE...
Issued at 345 AM HST Tue Jul 21 2026
The trade winds will hold at mostly moderate speeds through
today as a subtle trough moves through the state. Trade winds
strengthen to fresh and locally strong speeds Wednesday and could
strengthen another notch late Thursday into Friday with widespread
strong trade winds possible towards the end of the work week.

The High Surf Advisory for south facing shores has been cancelled
due to the downward trend shown on the nearshore and offshore
buoys. The current south-southeast swell should slowly fade over
the next few days.

A powerful low pressure system tracked eastward well south of
Tasmania and New Zealand last week. OSCAT pass showed a wide fetch
of storm force winds with altimeter passes showing seas above 50
feet. This should translate into very long period forerunners
arriving as early as early Wednesday morning and steadily filling
in throughout the day Wednesday and peaking on Thursday out of the
south-southwest. Surf should reach advisory thresholds by
Thursday. The very long-period energy will make for inconsistent,
but powerful waves when they arrive. Several days of advisory
level surf is expected starting from Thursday and possibly
continuing through Sunday as reinforcing energy arrives over the
weekend.

Surf along east-facing shores will remain slightly below seasonal
levels today as the trades ease upstream of the islands. The Hilo
buoy this morning is showing a slight increase across the 12 to
14 second energy bands, which was likely generated by former TC
Elida. Easterly swell from TC Elida should peak on Wednesday near
seasonal levels. Stronger trade winds will also support an
increase of short-period energy by Wednesday, This weekend,
larger surf for east shores generated by Hurricane Fausto is
possible and could bring advisory level surf along east facing
shores as well.

Surf along north-facing shores will remain at flat to tiny levels
through the weekend.

&&

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

&&

$$

SHORT TERM UPDATE...JVC
DISCUSSION...Blood
AVIATION...Parker
MARINE...Kino