460 
FXHW60 PHFO 171345
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Wed Jul 17 2019

.SYNOPSIS...
Trade wind weather will continue through the remainder of the week 
into early next week, thanks to high pressure far north of the 
area. Clouds and passing showers will favor windward and mauka 
areas. Leeward sections of the Big Island will see clouds and 
showers mainly during the afternoon and evening hours. 

&&

.DISCUSSION...
Locally breezy trade winds prevail across the islands early this 
morning as a surface high persists far north of the state. An upper 
level trough in the island vicinity is still bringing some airmass 
instability in the island vicinity, especially over the western 
islands. Early morning Lihue sounding pretty much confirmed that, 
depicting a somewhat moist and unstable airmass, with low level 
moisture extending to about 8 thousand feet. Early morning Hilo 
sounding depicted a more stable and drier airmass, with low level 
moisture extending to about 6 thousand feet. Low clouds embedded in 
the trade winds are passing over the islands at times, bringing some 
showers to mainly windward and mountain areas. Winds are strong 
enough to carry some of the clouds and showers to the lee areas of 
the smaller islands. 

The upper level trough in the island vicinity will move northwest 
today. As such, airmass in the island vicinity will become more 
stable. Latest forecast solutions still hinted a slight decrease in 
moisture across the area today, though satellite imagery does show 
lines of low clouds just east of the islands. These lines of clouds 
will bring more showers to the area, at least through the rest of 
the morning. Meanwhile, the aforementioned high will persist far 
north through the rest of the week, and strengthen slightly through 
Thursday. Overall, breezy trade wind weather will prevail across the 
islands through the next few days. The airmass may still be unstable 
enough for a slight chance of an upslope thunderstorm over the Big 
Island this afternoon. Forecast models hinted an increase in 
moisture for the islands Thursday. Hence the islands may see a 
slight increase of passing clouds and showers then.

The high to our north is expected to slowly weaken by the weekend 
into early next week. This points to a slight downward trend in 
trade wind speeds for that period. Furthermore, the aforementioned 
upper level trough may sag back southward, closer to the state. This 
may lead to a slight uptick in shower activity, mainly for windward 
and mauka areas. Daytime heating will continue to allow for clouds 
and showers to form over the leeward Big Island slopes each 
afternoon and evening.

&&

.AVIATION...
A 1031 mb high north of the Hawaiian Islands will generate breezy to 
occasionally windy easterly trades for the next 24-hours. Expect 
scattered showers to affect mainly windward and mauka areas with 
isolated showers passing over and onto the leeward side. 

Periods of MVFR conditions could develop along the windward slopes 
through early this morning, as low clouds and SHRA may create 
mountain obscuration.

AIRMET Tango remain in effect below 8000 ft for areas South thru 
West of mountain ranges due to tempo moderate turbulence.

&&

.MARINE...
High pressure north of the state will keep fresh to strong trades in 
place through Friday. The trades are expected to ease slightly over 
the weekend, as high pressure to the north weakens. A Small Craft 
Advisory (SCA) remains in effect for most waters between Oahu and 
the Big Island. Fresh trades are expected for the remaining waters 
not in the SCA, with winds likely flirting with SCA levels at times. 
We will continue to monitor observational and model trends over the 
next few days, and expand the SCA to additional marine zones if 
needed. 

The current south swell will continue to slowly subside today and 
tonight, with only small background south and southwest swells 
expected Thursday through the weekend. A bit of a boost in south 
shore surf is possible early next week, as a pair of overlapping 
southwest swells move through. Locally strong trade winds will 
produce choppy waves along east facing shores into the weekend. East 
shore surf will get a boost Thursday and Friday as the upstream 
fetch of trade winds increases. Surf is expected to stay below 
advisory levels along east facing shores Thursday and Friday and 
slowly lower over the weekend as trades ease.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big 
Island Southeast Waters.

Small Craft Advisory until 6 PM HST Friday for Oahu Leeward 
Waters-Kaiwi Channel-Maui County Windward Waters-Maui County 
Leeward Waters.

&&

$$

DISCUSSION...Hui
AVIATION...Thomas
MARINE...Jelsema