412 
FXHW60 PHFO 130146
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
346 PM HST Wed May 12 2021

.SYNOPSIS...
A broad surface ridge far north of the island chain will maintain
moderate to locally breezy trade winds into this weekend. Low 
clouds and passing trade showers will continue to favor windward 
and mauka areas, while brief showers are possible over some 
leeward sections. 

&&

.DISCUSSION...
No changes to the forecast with the afternoon package. 

A broad ridge remains to the north of the islands with moderate to
locally breezy trades over the region. Expect the trades to stick
around into the weekend, and likely beyond. Clouds and showers 
riding in on the trade wind flow will keep most of the shower 
activity focused over windward and mountain areas. An upper-level 
trough is evident in water vapor imagery north of the islands, and
its digging toward the south-southeast. A weak short wave trough 
is moving through the region, however a drier airmass at the lower
levels is limiting its impact. 

The upper level trough is expected to stall out to the northeast 
of the islands, and eventually lift out early next week. How much 
of an interaction this feature has on the clouds and showers being
carried in on the trade wind flow remains to be seen. The models 
are showing a decrease in the low-level moisture sources upstream 
of the state, and if this pans out, this could limit the cloud 
cover and precipitation as we head into the weekend. Another short
wave swinging through late this weekend could help to enhance 
shower activity if there is enough moisture with the system. The 
current forecast keeps a typical trade wind weather pattern later 
this week until we see evidence that there may be an enhancement 
in clouds and showers.

&&

.AVIATION...
Surface high pressure well north of the state will continue to 
bring moderate trades through the forecast period. This flow 
pattern will generate weak to occasionally moderate turbulence on 
the lee side of mountain ranges. 

For the next several hours, isolated showers will generally be 
focused along windward facing coasts and slopes. Expect an 
increase in shower coverage along windward locations tonight. 
This activity may bring brief periods of MVFR ceilings and 
visibility.

No AIRMETs are currently in effect.

&&

.MARINE...
Surface high pressure residing north and northeast of the state
the next several days will maintain moderate to fresh northeast 
to east trade winds. The most recent ASCAT satellite pass has 
verified the need for a Small Craft Advisory (SCA) over the
windier areas surrounding the easternmost islands. The SCA is in
effect for locally strong winds across the Pailolo and Alenuihaha
Channels, Maalaea Bay and those waters south of the Big Island
and has been extended through Thursday afternoon. 

Summerlike surf conditions will hold through the week. Surf will 
remain up along south facing shores as a series of overlapping 
small, long period swells originating from the southern hemisphere
pass around the islands. Eastern exposed coasts will experience
choppy wind wave conditions due to the persistent nature of 
these moderate to fresh onshore trades. Several consecutive days 
of persistent trade flow has produced a fully-developed sea state
and, along with a limited upstream easterly wind fetch, will 
ensure relatively small surf along east facing shores for the rest
of the week. Surf along north facing shores will remain low as 
a northwest swell completely fades into tonight. 

&&

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


&&

$$


DISCUSSION...M Ballard
AVIATION...Thomas
MARINE...Blood