593 
FXHW60 PHFO 310124
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
324 PM HST Mon Aug 30 2021

.SYNOPSIS...
Expect light trades and afternoon sea breezes, with a few showers
along windward sections at night and over leeward slopes and 
coasts in the afternoons through Tuesday. For Wednesday and 
beyond, breezy trade winds will bring mainly windward and 
mountain passing showers.

&&

.DISCUSSION...
A weak surface trough will move slowly westward across the 
islands tonight and Tuesday. This trough has interrupted the 
trade wind flow enough for afternoon seabreezes to develop today 
and this condition is expected again Tuesday. A few afternoon 
clouds and showers have developed across the leeward sides of the 
islands where the light trades converge with sea breezes and 
upslope flow. 

Precipitable water is around 90% of normal indicating a fairly 
dry airmass and a stable inversion at around 8 or 9 thousand feet 
are limiting the daytime seabreeze/upslope showers and afternoon 
rainfall accumulations have been generally light at less than 
0.20, with Puu Opae on Kauai and Honouliuli on Oahu getting the 
most rain so far at 0.52 and 0.43 inches respectively. These few 
leeward showers will continue for a couple more hours, with the 
chance for showers transitioning to the windward sides overnight 
and tomorrow morning. Expecting a similar pattern Tuesday 
afternoon with clouds and a few showers on leeward slopes and 
coasts.

Southwesterly flow aloft around the upper level trough to the 
north and northwest of the state will bring high clouds at times 
over the next few days.

The trough at the surface continues westward and moves west of 
the state midweek. Breezy trade winds return through the day 
Wednesday and continue into the coming holiday weekend with the 
surface high moving southward and tightening the pressure 
gradient across the state.

The GFS is showing a modest surge in moisture from the southeast 
as the east-southeasterly trades fill in behind the westward 
moving trough. This could give the islands a bump up in windward 
trade showers if this happens, although the EC seems less bullish 
on this scenario. Have just nudged PoP higher in the Wednesday 
night to account for this. 

Both GFS and EC models hint at another increase in moisture 
riding in on the trades is predicted late Friday into the weekend,
for another bump up in the chance of trade showers over the 
typically wetter locations.

&&

.AVIATION...
Trade winds easing will give way to a land and sea breeze 
regime through Tuesday. Clouds and showers will shift from the 
typical windward and mauka locations to leeward and interior areas
through the afternoon periods where sea breezes develop. MVFR 
CIGS/VSBYS are possible in and around showers. Otherwise, VFR 
conditions will prevail. No AIRMETS are in effect.

&&

.MARINE...
Trade winds will remain rather light through Tuesday night as a
surface trough tracks westward to the north of the islands. As 
the trough exits to the northwest of the state Wednesday and 
Wednesday night, the trades will increase from east to west 
across the marine area. Small Craft Advisories will likely be
required for the typically windy waters around Maui County and 
the Big Island Thursday through Saturday, and may be needed for 
most if not all waters on Friday as the trades peak. 

No significant swells are expected during the next 7 days. A 
series of small south and southeast swells will keep some small
surf rolling into south facing shores through the period.
Meanwhile, east shore surf will remain very small through 
Wednesday, then increase to near normal levels Thursday through 
the weekend as the trades increase over and upstream of the 
islands.

&&

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

&&

$$


DISCUSSION...Brenchley
AVIATION...Gibbs
MARINE...Jelsema