375 
FXHW60 PHFO 071940
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
940 AM HST Tue May 7 2019

.SYNOPSIS... 
Light and variable winds will continue through Wednesday, with light 
trade winds expected to return Thursday and Friday. Trade winds will 
then gradually strengthen over the weekend, becoming locally breezy 
early next week. With the light winds, afternoon sea breezes will 
drive cloud formation over interior and mauka areas, with little in 
the way of rainfall. The returning trade winds will tend to focus 
clouds and showers over windward areas, but the island atmosphere 
will remain stable, and only brief passing showers are expected. 

&&

.DISCUSSION...
The islands lie in an area of light and variable winds, as a complex 
area of low pressure lies between the islands and the trade wind 
supporting high to the NE. Morning soundings show a dry and stable 
air mass in place, with a strong subsidence inversion based between 
5000' and 6000', and PWAT near 1.1". Satellite shows nearly clear 
skies over windward waters, and partly to mostly cloudy skies over 
leeward waters, where radar is picking up a few light showers. Over 
the islands, mostly sunny skies prevailed early this morning, except 
for an area of stable low clouds that was lurking over Oahu. 
However, latest images show stable low clouds increasing over the 
lower slopes of all islands over the last hour or so.

The complex low NE of the islands will gradually dissipate over the 
next 48 hours or so, as a relatively weak high pressure cell passes 
well N of the islands. Latest guidance indicates that a weak trough 
will linger NE and N of the islands through Friday, so although we 
are expecting the high to support light trade winds on 
Thursday/Friday, wind speeds will likely be sufficiently light to 
allow land and sea breezes to dominate winds over land. As the 
trough dissipates and another high builds to the NW and N of the 
islands over the weekend, moderate trade winds are expected. The 
high will sit far NE of the islands next week, and seasonable 
moderate to locally breezy trade winds are expected. 

The light winds will allow afternoon sea breezes to drive cloud and 
shower formation over island interiors, but little significant 
rainfall is expected as the island atmosphere will be stable due to 
the presence of a mid-level ridge that will be building over the 
islands this weekend. So, even as trades return, passing windward 
showers are expected to be brief, with little significant 
accumulation.

&&

.AVIATION...
Light flow over the region today will allow for weak diurnal sea 
breeze/land breeze development. Expect variable low cloud cover with 
bases generally above 2500 feet MSL. Other than ISOL -SHRA that may 
develop over the interior later this afternoon, conditions will 
remain VFR.

No AIRMETS are anticipated today. 

&&

.MARINE...
Light and variable winds due to a weak trough of low pressure over 
the region will continue through Wednesday and weaken north of the 
state Thursday and Friday. A ridge of high pressure will build 
northwest of the state Thursday and will bring light to moderate 
trades Thursday through the weekend. Despite the return of light to 
moderate background east to northeast trade flow through the second 
half of the week, overnight and early morning land breezes followed 
by late morning/afternoon sea breezes will remain likely near most 
coasts each day. 

Surf along north facing shores will lower today as the current small 
nine second swell eases. A fresh northwest swell associated a gale 
that has tracked east of the Date Line near the Aleutians over the 
past couple of days will build down the island chain late Wednesday, 
then peak Wednesday night through Thursday before easing into the 
weekend. A small northwest swell associated with a compact gale that 
is forecast to develop Wednesday night into Thursday as it tracks 
east-northeastward across the Date Line will be a possibility late 
Sunday through Monday. Surf along north and west facing shores 
associated with this feature, if it evolves, will be minimal. 

Surf along south facing shores will remain small through midweek 
with mainly a combo of south-southeast and south-southwest swell 
energy continuing. An upward trend is expected late Thursday through 
the weekend due to an active pattern down south featuring two 
powerful lows passing far south of New Zealand within Hawaii's swell 
window. Back-to-back long-period south swells moving through locally 
will result with the first one filling in by Thursday night and the 
second one filling in Saturday out of the same direction (190 deg). 
The first swell has already begun to move through the Pago Pago 
buoy, which increases the confidence for an arrival locally by 
Thursday night. The second one will be the larger of the two, which 
may result in the first high surf advisory of the season for south 
facing shores Saturday night into Monday. The factors that reduce 
forecast confidence in heights reaching advisory levels is that the 
northern extent of this fetch was farther south and aimed more so at 
the Americas. Confidence will increase by Thursday as this energy 
moves through the Pago Pago buoy. 

&&

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

&&

$$

DISCUSSION...Birchard
AVIATION...JT
MARINE...Kino