Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 201355

Area Forecast Discussion
National Weather Service Honolulu HI
355 AM HST Sat Jul 20 2024

Moderate trade winds will continue over the next few days, with
breezy to locally windy trades returning by early next week. A
weak disturbance riding in on the trades will increase clouds and
shower activity through this evening. Another weak disturbance
will move across the islands on Tuesday. Significant rainfall is
not expected from either disturbance, but they should provide
some beneficial rain for windward and mauka areas.


A weak trough over the Kaiwi Channel will continue to move across
the rest of the state today. Clouds and embedded showers continue
to move into Windward Big Island early this morning with localized
areas of moderate to heavy rainfall across the Hamakua Coast down
to Puna and along the Kau Coast. The highest rainfall total over
the last 12 hours was 4.2 inches near Honolii. The wetter weather
has started to move into East Maui over the last few hours. The
12Z sounding at Hilo contained 1.81 inches of precipitable water
under a weakly unstable atmosphere, with CIMSS MIMIC PWATs showing
similar values over the Alenuihaha Channel. This setup continues
to support areas of moderate to locally heavy rainfall totals over
Windward Big Island and East Maui today, but flooding concerns
remain minimal. Otherwise, the rest of the state can expect a
slight uptick in windward clouds and showers through tonight as
the moisture plume continues to move east across the islands.
Leeward areas will mainly see an increase in cloud cover through
tonight with some passing showers.

Drier conditions return Sunday with breezy trades expected by
Monday. Breezy to locally windy trade will then continue through
much of the upcoming week as high pressure strengthens far
northeast of the state.

Another disturbance associated with an area of deeper moisture
currently near 137 degrees West is expected to move across the
state on Tuesday, with model PWATs around 1.8 inches. This system
should bring more widespread clouds and showers to windward and
mauka areas of all islands. With the stronger trades in place
expect some of these showers to spillover into leeward areas at
times. Expect a return to more typical trade wind weather
conditions behind the disturbance with strong trades continuing
through the end of the upcoming week.


Moderate to locally breezy trades will continue into the weekend.
A passing disturbance is expected to bring an increase in
windward SHRA to the east end of the state through the rest of
today. Low cigs should favor windward and mauka areas with brief
periods of MVFR possible. Otherwise, VFR should prevail.

AIRMET Sierra for mtn obsc is in effect for windward Big Island.
Conds should improve by mid morning.


A high pressure system far north of the Hawaiian Islands will
will begin to strengthen the trade winds into the fresh to
locally strong afternoon as the high center strengthens. Trade
wind speeds will be strong enough to support Small Craft Advisory
(SCA) conditions over the windier waters and channels near Maui
and the Big Island starting this evening and lasting through much
of next week. An SCA was issued for these waters starting tonight.

Background south swell energy pulses are forecast to continue
with surf remaining below average through much of next week.
Small, choppy surf is expected for east facing shores for the
next several days due to continued trade winds. Surf then becomes
increasingly rough along east facing shores as locally strong
trades increase early next week.

Spring tides will peak this weekend, and local tide gauges
indicate water levels are already running above guidance. Water
levels are currently running at least 1 foot higher than the Mean
Higher High Water (MHHW) threshold at Hilo, Kahului, and Honolulu
and have exceeded the 1 foot threshold at Honolulu. The Coastal
Flood Statement for isolated minor flooding has been extended
through Monday evening.


Small Craft Advisory from 6 PM this evening to 6 AM HST Monday
for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters.