622 
FXHW60 PHFO 111411 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
411 AM HST Fri Dec 11 2020

.SYNOPSIS...
Trade winds will return today, strengthen to moderate levels this
afternoon, and become breezy by Saturday. The trades will then 
ease again by Sunday as a new front approaches from the northwest.
Fairly typical trade wind weather featuring mainly windward and 
mauka showers will prevail through the weekend. A more moist and 
unstable airmass could bring an increase in shower coverage and 
intensity to much of the state next week.

&&

.DISCUSSION...
Currently at the surface, a weakening cold front is located 
around 200 miles northwest of Kauai, while a 1026 mb high is 
centered around 1750 miles east-northeast of Honolulu. Light 
trade winds remain in place over the eastern islands, while the 
western half of the state remains under light and variable winds 
with land breezes present in most areas early this morning. 
Infrared satellite imagery shows clear to partly cloudy 
conditions in most areas, with a couple pockets of more extensive
cloud cover over windward Big Island and leeward Kauai at the
moment. Meanwhile, radar imagery shows a couple light showers
moving into windward areas, with mainly rain free conditions in
leeward locales. Main short term concerns revolve around trade 
wind trends and rain chances through the weekend.

The front northwest of the state will move closer to the island 
chain today, then stall out around 100 miles northwest of Kauai 
tonight. A new high will build rapidly eastward to the north of 
the front during the next few days, with the high passing by 
several hundred miles north of the state on Saturday. As a result,
we should see light and variable winds hold over the western 
islands early this morning, while light trades hold over the 
eastern end of the state. Light trades are expected to overspread
the entire island chain this morning, then strengthen to moderate
levels this afternoon. The trades will continue to strengthen 
tonight, then peak at breezy levels Saturday. The trades will 
then diminish into the light to moderate range by Sunday, lightest
over the western islands, as the next cold front approaches from 
the northwest. Aside from some minor fluctuations in strength, the
light to moderate trade wind regime should generally hold in 
place through early next week, possibly becoming light and 
variable Tuesday and Wednesday. Both the ECMWF and GFS are now 
showing a well defined surface trough and elongated area of low 
pressure developing east of the state, with high pressure to the 
northwest of the islands late next week. If this materializes, a 
return of moderate to breezy northeasterly trades may overspread 
the state for the tail end of next week.

As for the remaining weather details, the returning trades should
bring a transition back to more typical windward/mauka focused 
showers through the weekend. Low level moisture is expected to 
remain rather low during this period, so only brief passing
showers are expected. There could be an increase in shower 
coverage over windward Big Island Saturday night and Sunday
however, as a slug of precipitable water values above 1.5 inches 
gets drawn northward.

The forecast is more uncertain next week, as the ECWMF and GFS
continue to show some notable differences. Overall however, the 
latest trends suggest a more moist and unstable airmass will move 
over the state. If light to moderate trades hold on through the 
middle of next week, showers should favor windward and mauka 
areas, with scattered showers developing in afternoon hours over 
leeward areas then fizzling out in the evening. Additionally, a 
few of these showers could be on the heavier side due to the more 
unstable airmass in place. A rather wet pattern could develop late
next week over the eastern islands, but confidence in this remains
low at this time. We'll continue to monitor trends closely over 
the next few days and hold off on making any significant changes 
until details become more clear.

&&

.AVIATION...
No AIRMETs are in effect, and VFR conditions will prevail.

A surface ridge just north of the area will move farther north and
strengthen over the next couple of days. The ridge is producing 
moderate easterly trade winds near the Big Island of Hawaii with 
gentle variable winds elsewhere. Radars show scattered showers 
moving over the east side of the Big Island in the trade-wind 
flow. Land breezes have cleared most showers from the smaller 
islands.

The trade winds will continue to carry clouds and showers over the
east side of the Big Island today. As the ridge builds north, trade
winds will spread over the smaller islands, but sea breezes may have
a chance to develop and produce some interior cloudiness before the
trade winds become established. 

&&

.MARINE...
A surface ridge axis from far northeastern high pressure is 
extending north of the chain. This has been the impetus for 
recently weak and variable winds over more western Hawaiian 
waters. This pressure gradient back across the islands will 
restrengthen as high pressure builds in north of the state. This 
should increase the trades to moderate and locally strong 
magnitudes late today through Saturday. This has prompted a Small
Craft Advisory (SCA) for Maalaea Bay, the Pailolo and Alenuihaha 
Channels and those waters south of the Big Island from tonight 
through at least Saturday evening. Winds are expected to trend 
down again on Sunday as high pressure pulls off further to the 
northeast early in the week.

Surf is expected to remain below High Surf Advisory (HSA) levels 
along all shores through Saturday. Several North Pacific low 
pressure systems producing gale force winds will generate a 
series of northwest swells that will be directed towards the
islands from Saturday into early next week. A pair of northwest 
swells are expected to arrive this weekend that may lift surf to 
near advisory levels for north and west-facing shorelines Sunday. 
These swells will trend down Monday and Tuesday with a slightly 
longer period north to northwest swell building in Wednesday or 
Thursday.

Expect choppy surf along east-facing shores in response to 
strengthening trades today and Saturday. Small, long period 
southwest swells will continue to provide small south-facing 
shoreline surf the next couple of days. The aforementioned 
northwesterly swells combined with trade wind waves will cause 
seas to remain slightly elevated, although likely under SCA 
criteria, through mid week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory from 6 PM this evening to 6 PM HST Saturday 
for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island 
Leeward Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Donaldson
MARINE...Blood