556
FXHW60 PHFO 151340
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
340 AM HST Sun Sep 15 2024

.SYNOPSIS...
Locally breezy trade winds will persist this week, delivering
passing showers that will favor windward areas. Deeper moisture will
move over the islands tonight and Monday, likely bringing increased
shower coverage, especially over the Big Island, where some heavy
showers may develop.

&&

.DISCUSSION...
Surface high pressure far NNE of the islands will remain nearly
stationary this week, supporting breezy and locally gusty trade
winds. A slight decrease in wind speeds is possible by next weekend
as the high weakens. Generally speaking, fairly typical trade wind
weather is expected, with brief windward showers occasionally
spreading a few sprinkles leeward, most likely during nights and
mornings.

A caveat to the typical trade wind forecast is an area of increased
moisture approaching from the E. More specifically, the leading edge
of a 300-mile-wide area of broken to overcast low- and mid-level
clouds lies about 150 miles E of the Big Island. UW-CIMSS MIMIC
analyses indicate PWAT near 2" in this area, supported by what model
guidance indicates is a sharp 700 mb trough.

As this trough moves W over the islands tonight and Monday, moisture
will extend as high as 12-15 kft, mainly over the Big Island,
bringing the potential for some heavy showers. While the moisture
increase over the smaller islands is not expected to be as deep, an
increase in windward showers is likely. Additionally, dew points in
the low- to mid-70s will make it feel muggy statewide on Monday.
After the trough moves W of the islands Tuesday and Wednesday, a
return to a fairly typical trade wind weather pattern is expected as
dew points drop slightly.

&&

.AVIATION...
High pressure centered far north of the state will maintain moderate
to breezy trades over the next couple of days. Clouds and showers
will favor windward and mauka areas, though the temperature
inversion heights will remain elevated enough to allow occasional
showers to pass over island terrain into leeward areas. Shower
coverage and intensity will be greatest through the early morning
hours today and then again tonight as a plume of deeper moisture
moves in from the southeast. Periodic MVFR conditions are expected
in heavier showers. Otherwise, VFR conditions will prevail.

With the increased trade winds, AIRMET Tango for low-level
turbulence over and downwind of terrain is in effect and will likely
continue into tonight.

AIRMET Sierra is in effect through this morning for tempo mountain
obscuration across windward areas due to low clouds and showers.
This AIRMET will likely be needed again by this evening for at least
the southern end of the state.

&&

.MARINE...
Surface high pressure far north northeast of the waters near 45N
will continue to provide moderate to locally strong trade winds
through the first half of the week. A Small Craft Advisory has been
extended for the windier waters and channels of Maui County and the
Big Island through Monday night. A slight uptick in trade winds is
expected Monday and Tuesday as the pressure gradient strengthens.

Surf along east facing shores will remain choppy through the first
half of the week due to persistent trades locally and upstream of
the islands. A small long period south swell will slowly decline
today. A combination of background south and southeast swells will
keep the surf from going flat over south facing shores through the
first half of the week. North facing shores will remain nearly flat
through much of the week. Models show a gale low developing and
tracking along the Aleutian Islands that may send a small northwest
swell into the local waters Friday into Saturday.

Water levels at local tide gauges are running over half a foot above
predicted and are expected to reach above the 1 foot Mean Higher
High Water threshold for coastal inundation over the next several
afternoons due to above normal water levels coinciding with the
spring tides. The Coastal Flood Statement is now in effect for this
threat through Tuesday and may need to be extended through Wednesday.

&&

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

&&

$$

DISCUSSION...Birchard
AVIATION...Farris
MARINE...Shigesato