007 
FXHW60 PHFO 210157 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
357 PM HST Sun Sep 20 2020

.SYNOPSIS...
A bit of an increase in shower activity is expected through
tonight, mostly over windward areas, and mostly overnight and 
into the early morning hours. Drier air is expected Monday 
through midweek, which will limit shower coverage. Moderate trade 
winds are more likely to be locally breezy Wednesday and Thursday,
with a bit of a downward trend next weekend.

&&

.DISCUSSION...
Have made some tweaks to the PoPs for tonight and tomorrow mostly
near Kauai, since showers have persisted over the western end of
the island chain today. Have also adjusted QPF values through the
week to better reflect a blend of the models. For the short term,
that involved a boost to Kauai QPF to better reflect the rainfall
totals we have been seeing today. Little change to the winds. The
morning ASCAT pass showed winds over the waters near the islands
at 20 kt or lower, but winds did pick up a little this afternoon
with the diurnal cycle.

High pressure to the north of the islands will continue to bring
moderate trades to the region. The high is expected to be
disrupted by a front passing north of the islands over the next
day or two, with a new high settling in behind the front. The new
high will help to boost winds a little during the second half of 
the week, but then look for winds to weak as we head into the
weekend. The front will introduce additional moisture upstream of
the islands which will likely be carried in on the trades during 
the second half of the week.

Water vapor continues to show the upper level low, now about 475
miles to the west-southwest. This feature has been moving to
the east, and we have seen the high clouds over Kauai and Oahu
this morning shift more towards Kauai. Additional high clouds are
being pulled up over the southern end of the island chain. 

The global models remain in good agreement with an upper level 
trough/low to the northwest of the islands for the next 24 hours
or so. They are also in good agreement with the development of a 
closed upper low north-northwest of the islands along the upper 
trough Tuesday night. The GFS and ECWMF keep the low/trough 
further to the northwest during the second half of the week, but 
bring it towards the islands as we head into the weekend. That is 
when the models diverge in their handling of the upper low, so 
will have to keep an eye on that over the next few days to see how
the models handle it. Not expecting any significant weather from 
this upper low, but it could help to increase shower activity 
depending on how close it comes to the islands.

&&

.AVIATION...
Sea breezes have produced broken to overcast low clouds and a few
showers over the southwest section of the Big Island of Hawaii. 
These clouds and showers will persist through this evening. A 
ridge far north of the area will maintain moderate to locally 
strong east winds over the area. These winds will push some 
showers over east sections of the islands. Isolated MVFR ceilings 
and visibilities are likely but the conditions are not expected to
be widespread enough to warrant an AIRMET. 

&&

.MARINE...
Moderate to locally strong trades will hold through tonight, then
slightly weaken to fresh speeds as the high to our northeast 
weakens. Another high will build north of the state towards the 
middle of the week and will maintain locally fresh trades through 
around Thursday. Trade winds may decrease Friday into the weekend
as the ridge of high pressure shifts slightly closer to the state.  
A Small Craft Advisory remains in effect through late tonight for
the typically windy areas around Maui County and the Big Island.
Winds will continue to remain near borderline advisory levels
throughout the week for these windier areas. 

A small 3 foot north swell filled in during the day today and 
will likely hold through Monday morning then steadily decline into
Tuesday. A larger 4 to 6 feet long-period north-northwest swell 
will begin to fill in on Wednesday and peak Wednesday night into 
Thursday for north and west facing exposures. Surf along east 
facing shores will remain small through much of the week, but 
northeast facing exposures should see some moderate surf from the 
north-northwest swell during the second half of the week.

The current south-southwest swell looks to have peaked earlier 
today and will be on a slow decline over the next few days. A new 
smaller southwest swell should begin to fill in on Monday and will
help keep surf heights near the summer average (3 to 5 feet) 
during the first half of this week. Another small south-southwest 
swell is possible Friday into Saturday. 

&&

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


&&

$$


DISCUSSION...M Ballard
AVIATION...Donaldson
MARINE...Kino