652 
FXHW60 PHFO 191349
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
349 AM HST Tue Oct 19 2021

.SYNOPSIS...
A ridge of high pressure approaching the islands will make for
gentle trades the next couple of days. A dry and stable airmass
will give lots of sunshine and relatively few showers to the Aloha
State. The remnants of an old front will reach Kauai Thursday, and
might also spread to Oahu Thursday night or Friday, bringing an
increase in clouds and some showers. Trades will start to 
increase Thursday and become breezy over the weekend. A dry and 
stable airmass will also return this weekend with fine weather 
expected.

&&

.DISCUSSION...
No big surprises in the 12z soundings, with slightly lower 
inversions and similar precipitable water and moisture depth as in 
the 00z soundings. Satellite and radar showing relatively few 
clouds and showers. With mid-level ridging capping the vertical 
cloud growth, trade wind showers should be fairly sparse today and
where rain does fall, amounts should be pretty light. Lots of 
sunshine expected again today as well. 

Quiet weather will persist through tonight and Wed as a surface 
ridge about 275 miles NNE of the islands continues pushing slowly 
toward the state. Generally gentle background trades are expected 
today (although locally breezy in the typically windiest 
spots) and diurnal land and sea breeze circulations a little more
prevalent in the usual areas more sheltered from the trades. 
Winds on Wed will be even slightly lower than today, but the 
models insist that we won't completely lose the background trades 
even with the dissipating ridge coming to within about 75 miles of
Kauai. 

The remnants of a dissipating cold front about 500 miles N of 
Kauai are expected to bring an increase in clouds and showers to 
Kauai and probably Oahu starting about Thu (for the Garden Isle) 
and persisting into Friday before falling apart. The low level 
moisture will have marginal upper level support to work with in 
the form of a weak upper trough, but overall rainfall amounts are 
expected to be fairly modest with the frontal remnants. 

It looks like after that, breezy trades return and bring drier 
and more stable air back to the Aloha State for the foreseeable 
future. Over the weekend, 700 mb temperatures reach double digits,  
model ensemble moisture depth drops back to 5000 to 6000 feet, and
precipitable water drops to nearly 1 inch. Even though this is the  
time of year when we typically expect to start seeing the weather 
get a little more active near Hawaii, the models don't show much 
of promise for significant rainfall into the longer range. This 
is not particularly good news with severe to extreme drought 
continuing in parts of the state.

&&

.AVIATION...
As a high pressure ridge moves towards the islands from the north,
northeast trade winds have been easing into the moderate range as
the pressure gradient loosens. Brief periods of low cloudiness 
and showers may affect mainly windward and mauka sections 
statewide from time to time, but overall conditions will be VFR as
the atmosphere becomes more stable.

No AIRMETs are in effect, and none are anticipated through today.

&&

.MARINE...
Moderate trades will be gradually trending down to generally light  
to gentle breezes the next couple of days as a series of North 
Pacific cold fronts weaken the ridge north of the islands. These 
fronts will cross the north offshore waters Wednesday and Thursday
and are expected to wash out before reaching the state. High 
pressure will re-establish itself north of the islands by Friday 
and this will strengthen weekend trades back into the moderate to 
locally strong category.

A series of north swells will move through the coastal waters this
week. A recent small north pulse will be reinforced by a larger, 
medium period north-northwest swell tonight through Wednesday. An
even larger north swell follows Thursday night and Friday that 
will likely drive late week north facing shore surf heights to 
High Surf Advisory levels. Kahului Harbor and other north facing 
harbors will become susceptible to harbor surges from this north 
swell. Weakened trades equates to lower east facing shore surf 
through the middle of the week. Strengthening trades on Friday 
will lead to increasing surf along the eastern shores with this 
heightened east wind wave chop persisting through the weekend. 
Small surf along the south facing shores will get a minor boost
today as a small, but relatively long 14 to 16 second period 
south swell travels around the chain. This swell will linger 
through Wednesday before tapering off at the end of the week.

&&

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

&&

$$

DISCUSSION...R Ballard
AVIATION...Kinel
MARINE...Blood