502
FXHW60 PHFO 230150
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST Thu May 22 2025

.SYNOPSIS...
An upper low near the state will bring a slight chance of thunderstorms
through Friday. High pressure to the north will drive breezy
trade winds and mostly windward showers. A decrease in trade
showers with drier conditions persisting into the middle of next
week.

&&

.DISCUSSION...
A 1035 mb surface high is centered far north of Hawaii, but is
driving breezy trade winds across the islands this afternoon.
Water vapor imagery shows an upper low just north of Kauai slowly
moving southeastward. Radar and visible satellite show widely
scattered low clouds and showers moving in from the east carried
by the trade winds, with the upper level feature providing a
little bit of enhancement to the showers. 00Z soundings show a
strong, but slightly elevated inversion and precipitable water
around 1.3 inches. Lihue mixed layer CAPE is sufficiently strong
1100 J/kg with 700-500 mb lapse rates 7.6 C/km. Most of the
instability is focused above the trade wind inversion, which has
been the limiting factor for thunderstorms today. Will continue to
carry isolated thunderstorm coverage around Kauai and Oahu
tonight and Friday, and the Big Island interior Friday afternoon
due to the sea breeze/instability combination.

The upper low will remain in the vicinity of Kauai and Oahu
tonight, then begin to lift northeastward on Friday allowing
warming and stabilizing aloft by Friday night. Other than the
thunderstorm chances, a wetter than normal trade wind pattern
should prevail during the next couple days, favoring windward and
mauka areas, along with more leeward spread to the shower
activity.

The surface high will maintain the breezy winds through the
weekend before weakening and sliding and closer to the state
Memorial Day through the middle of next week, resulting in an
easing of the trade wind flow back to moderate speeds. The
airmass will further stabilize and dry out over the state this
weekend, leading to a decrease in trade showers with drier
conditions persisting into the middle of next week.

&&

.AVIATION...
Moderate to locally breezy trade winds will persist into the
weekend. Showers will focus over typical windward and mountain
areas with a slight increase expected tomorrow morning as enhanced
moisture moves through. Currently an upper level low is expected
to provide enough instability to allow some of the showers to
become heavy. Isolated thunderstorms are possible through tomorrow
morning. These conditions could cause some locations to dip into
MVFR range due to low visibilities and ceilings, but VFR should
prevail for most of the period outside of any showers.

Isolated areas of upper level turbulence is possible over western
island areas where the upper level low resides. An airmet for
these conditions is possible for a brief time tonight.

AIRMET Sierra remains in effect for mountain obscuration over
windward portions of Kauai. Improving conditions have been noted
on FAA webcams and satellite on Oahu, Molokai, and Maui where the
AIRMETs have been cancelled. Additional mountain obscuration is
possible tonight as cloud bases lower below some of the higher
elevation peaks with the diurnal cycle.


&&

.MARINE...
High pressure to the distant NNW will maintain moderate to
locally strong trade winds through the weekend, then weaken early
next week to bring moderate to fresh trades to the area. An upper
level low will linger over the state through tomorrow, enhancing
trade wind showers and bringing the potential for isolated
thunderstorms, mainly over Kauai and Oahu waters. A Small Craft
Advisory for the windier waters and channels around Maui County
and the Big Island remains in effect through Friday.

Surf along south facing shores will gradually build tomorrow
through Saturday as a long period south-southwest swell is
expected to fill in, producing near seasonal average surf through
the weekend before declining early next week. Another long-period
south-southwest swell is expected to arrive Wednesday into
Thursday, bringing more near seasonal average surf to south facing
shores.

East shore surf will remain near seasonal average through the weekend
as trade winds persist, then gradually decline into midweek as the
trades weaken slightly.

Tiny surf will prevail along north facing shores through early next
week. A small to moderate medium period northwest swell will arrive
late Wednesday into Thursday of next week, bringing above seasonal
average surf.

&&

.HFO WATCHES/WARNINGS/ADVISORIES..
Small Craft Advisory until 6 AM HST Friday for Kaiwi Channel-
Maui County Windward Waters.

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


&&

$$


DISCUSSION...Foster
AVIATION...Tsamous/Pechacek
MARINE...Kino/Farris