Heavy Rain in Hawaii, August 3 to 4, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
936 AM HST Wed Aug 3 2022

.SYNOPSIS...
The light background wind pattern settling over the state will
allow local land and sea breeze circulations to dominate the
islands through Friday. Showers scattered across mainly windward
locations early today, will then become focused across island
mountain and interior sections each afternoon, before clearing
each evening, through the remainder of the week. Trade winds will
then restrengthen this weekend as a high pressure ridge settles
over the region. A remnant trough associated with former Tropical
Cyclone Georgette, will drift westward across the islands
enhancing shower activity early Monday into Tuesday.

&&

.DISCUSSION...
Radar trends this morning continue to show showers focused along
mainly windward locations, as trades continue to further weaken.
Satellite data shows a broken layer of lower level moisture
drifting over the islands this morning while an area of deeper
layer moisture, assoicated with the upper low, lingers northeast
of the Big Island. GLM lightning data has indicated a few strikes
continuing north of Maui and the Big Island this morning (about
120 miles north of HTO) in the vicinity of the coldest cloud top
temperatures and steepest mid level lapse rates (5.5-6 c/km).

Overall, expect the most unstable airmass and best chance for
thunderstorms to remain north of the islands today, as the upper
low slowly rotates north of the region before finally exiting
northeast tonight. However, enough instability (mid level lapse
rates, Showalter Index) remains to support a mention of an
isolated thunderstorm across portions of Maui, the Big Island,
and the adjacent waters through the afternoon. Additionally,
elevated inversion heights will enhance shower activity across the
remainder of the islands through today. A weak surface trough
north of the islands, a reflection of the upper low, will hinder
the typical trade wind flow and promote the lighter large scale
winds across this island through Friday. This will allow local
scale land and sea breezes to strengthen over each island. Sea
breeze winds will focus clouds and shower activity across island
mountain and interior sections each day through Friday, while land
breeze development around sunset, will diminish clouds and shower
activity each night.

Saturday will begin the transition back toward a more typical
trade wind pattern, as the upper low weakens and continues to lift
northward allowing a high pressure ridge to settle back into the
region. The trade winds are forecast to strengthen to moderate to
breezy for the weekend. This return pattern shift will focus
clouds and showers to more typical windward and mountain areas.
An easterly wave, the remnants of former Tropical Cyclone
Georgette, will drift into the Hawaii region early Monday,
enhancing showers over the Big Island and Maui, with showers
expected to spread westward and reaching Kauai Tuesday.

Long range guidance continues to show a tropical low passing
south of the Big Island around the middle of next week. If the
low develops and passes south of the islands, trade winds could
further strengthen as the surface pressure gradient increases.

&&

.AVIATION...
A weak low level trough will cause trade winds to be on the
lighter side through Thursday allowing for daytime sea breezes and
nighttime land breezes to develop. An upper low just north of the
Big Island will cause the airmass to be unstable over the east
end of the island chain. Some locally heavy showers and isolated
thunderstorms are possible into this evening for East Maui and the
Big Island including the adjacent waters.

VFR conditions prevail at all TAF sites and these conditions are
expected to continue throughout the day today. No AIRMETs are
currently in effect, and none are anticipated through this
morning. There is a chance that AIRMET Sierra for mountain
obscuration might be needed this afternoon for portions of the Big
Island or Maui.

&&

.MARINE...
An upper low and associated surface trough to our east will track
to the north and west, resulting in light trade winds over the
islands for the next few days. The upper low will also increase
the chance for isolated thunderstorms over the Maui and Big Island
windward waters today. Trades will strengthen again over the
weekend as high pressure builds in northeast of the area.

A small south swell will continue to fade through the day with
only small background south swells expected for the remainder of
the week. East facing shores will see a gradual increase in surf
over the next few days in response to the arrival of a small,
medium-period east swell from recent eastern Pacific tropical
cyclone activity. No other significant swells expected through the
forecast period.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...SWR
AVIATION...Burke
MARINE...TS