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Hawaiian Islands Synoptic Discussion and Guidance

997
FXHW60 PHFO 151939
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
939 AM HST Mon Jul 15 2024

.SYNOPSIS...
Breezy trade winds will ease to moderate strengthen Wednesday
through Friday as broad high pressure weakens northeast of the
state. Stable and somewhat dry conditions will prevail through at
least Friday, with light showers favoring windward slopes.

&&

.DISCUSSION...
A locally breezy and very stable summertime trade wind flow
continues. Broad high pressure driving the trades spreads across
the much of the central and eastern Pacific near 35N, though the
main high is centered roughly 1,400 miles northwest of Kauai, and
ridging aloft continues to produce very stable conditions with an
inversion based near 6,000 ft. Precipitable water is running
slightly below July average, and the nearby trade wind flow is
dominated by a field of shallow stratocumulus. In spite of this,
showers were surprisingly active early this morning, with many
windward stations measuring between 0.1 to 0.2 of an inch of
rainfall during the past 12 hours and a few topping a quarter of
an inch. These showers will rapidly diminish midday. Aside from
some clouds and a few showers on the South Kona slopes, leeward
areas will be mostly dry.

No significant changes are expected over the next few days. Trades
will ease to moderate strength Tuesday night and Wednesday as a
weakness develops within the ridge northeast of the islands.
Stable conditions will persist with limited moisture in the trade
wind flow. As a result, expect modest windward rainfall, and aside
from a few afternoon showers on Kona slopes of the Big Island,
leeward areas should be dry.

In the long range, trades may strengthen during the weekend, and
the GFS and ECMWF suggest that an increase in showers will be
possible.

&&

.AVIATION...
Breezy to locally windy trade winds will continue through tonight
then gradually ease through mid week. Showers and periodic low
clouds will favor windward and mauka areas, with a few showers
possible over leeward areas overnight. VFR conditions will
prevail, with brief MVFR is possible in passing showers.

AIRMET Sierra for mountain obscuration may be needed tonight as
shower coverage increase.

AIRMET Tango for moderate low-level turbulence lee of island
terrain is in effect and will continue through tonight due to
strong trades.

&&

.MARINE...
Surface high pressure to the north-northwest of the islands will
remain stationary over the next couple of days and maintain fresh
to locally strong trade winds. A Small Craft Advisory (SCA)
remains in effect for the typical windier waters around Maui
County and the Big Island through Tuesday. As the high pressure
drifts northeast, trade winds look to decrease below SCA criteria
Wednesday through Friday.

The current long period south swell has peaked overnight as the
PacIOOS Barbers Point buoy peaked around 5 feet 17 seconds. The
spectral density observations from the Barbers Point buoy
continues to show long period energy in the 16 to 18 second bands
through the morning hours and is expected to maintain surf
heights well into High Surf Advisory (HSA) criteria through the
day. The HSA for all south facing shores will remain in effect
through tonight, then gradually decline through Friday.

Rough east shore surf will remain slightly above July average
today. The short period wind wave energy will slowly decline as
trades upstream of, and eventually over, the islands weaken. East
shore surf will fall below average by Wednesday and will decline
further through Friday. No significant source of northerly swell
is due this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Tuesday for Niihau-Kauai
Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai
South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Leeward
South-Lanai Leeward-Lanai South-Maui Central Valley South-South
Maui/Upcountry-South Haleakala-Big Island South-Big Island
Southeast.

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Wroe
AVIATION...Ahue
MARINE...Shigesato

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office