141
FXHW60 PHFO 190152
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
352 PM HST Fri Jul 18 2025

.SYNOPSIS...
Rain chances increase over the weekend in response to increasing
moisture and instability across the island chain, with a focus
over the western end of the state and the leeward slopes of the
Big Island. Heading into early next week, a more typical stable
trade wind pattern will return with limited rainfall favoring
windward and mauka areas.

&&

.DISCUSSION...
The short term forecast focuses on the increasing instability and
moisture across the state through the weekend. Current satellite
and radar imagery show clouds and a few showers moving into
windward and mauka areas on the trades, along with clouds and
showers building over leeward Haleakala and the leeward Big Island
slopes. Some of these leeward showers have been pretty hefty,
with radar estimated rainfall rates exceeding an inch per hour at
times.

Upper air soundings show that the low level temperature inversion
eroded overnight at Hilo, hinting at the increase in low to mid
level instability accompanying the 700 mb trough that is
progressing northwestward across the eastern end of the state
this afternoon. The low level inversion at Lihue has also lifted
and weakened on this afternoon`s sounding, likely due to the
approach of the 700 mb trough from the southeast and a weak mid
level low edging in from the north. In addition to this
instability, CIMSS MIMIC Layer Precipitable Water satellite
imagery shows a large area of precipitable water values between
1.4 to 1.6 inches moving across the island chain from the east
this afternoon. Model guidance indicates that this large plume of
above average moisture will stick around through the weekend, with
a concentration near the western end of the state. With the
instability provided by both the 700 mb trough and the proximity
of the weak mid level low and the presence of abundant moisture, a
wetter trade wind pattern is expected through the weekend, with
clouds and enhanced showers favoring windward and mauka areas
across the western end of the state, and leeward slopes of the
Big Island and Haleakala each afternoon. Isolated thunderstorms
near Kauai cannot be completely ruled out as the instability
increases with the mid level low through the weekend.

Early next week, mid level ridging will build over the state and
a moderate to locally breezy stable tradewind pattern will
return. Then global model guidance suggests a weak mid level
shortwave trough will sweep by the western end of the state on
Wednesday, potentially helping to briefly enhance trade wind
showers across the western end of the state.

Model solutions begin to diverge towards the end of the forecast
period, but current guidance shows a low level trough/low
approaching from the east that may disrupt the trade winds,
causing local winds to weaken and shift out of the east-northeast
for the latter part of the week.

&&

.AVIATION...
High pressure far to the north will drive moderate to locally
fresh trade winds across the state. AIRMET Tango is in effect for
tempo moderate turbulence below 070 across all leeward areas. This
AIRMET may be able to be dropped Saturday morning as winds weaken
slightly.

VFR prevails statewide late this afternoon. An area of cloud and
showers is forecast to move in from the east later tonight and
will likely bring periods of MVFR conditions along windward
slopes. Will monitor for AIRMET Sierra conditions, but should
expect isolated mountain obscurations.

&&

.MARINE...
High pressure will remain nearly stationary far northeast of the
state through the middle of next week. Fresh to locally strong
trades will persist through tonight then drop slightly as a weak
low-level trough moves through the state from the east through
the weekend. The Small Craft Advisory (SCA) for the windier waters
and channels around Maui County and the Big Island has been extended
through tonight. The SCA can likely be dropped by Saturday morning
as trade winds continue to gradually decline to gentle to locally
fresh through the forecast period.

A mixed southerly swell will provide average surf along south
facing shores through early Saturday. A new small, long-period
southwest swell will fill in slowly Saturday, peak over the
weekend, then decline slowly through early next week.

Surf along east facing shores will continue to remain choppy due
to the fresh to locally strong trade winds before declining
slightly over the weekend. Surf along north facing shores will
remain nearly flat through the forecast period.

Peak high tides associated with the lunar cycle could lead to
minor coastal flooding along shorelines and low-lying coastal
areas next week Monday through Wednesday during the daily peak
tide each afternoon.

&&

.FIRE WEATHER...
Fire weather concerns will be low this weekend as a result of a
wetter pattern. Trade winds will remain moderate to locally breezy
the next couple of days with a higher frequency of showers. Drier
weather is expected to return early next week. This may increase
the fire weather threat over those leeward areas that may not
receive the full benefit of significant weekend rain.

&&

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

&&

$$

DISCUSSION...Farris
AVIATION...Foster
MARINE...TS
FIRE WEATHER...Farris