772 
FXHW60 PHFO 111332
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
332 AM HST Fri Jan 11 2019

.SYNOPSIS...
Mostly dry conditions along with light trades will prevail across
the state through the weekend and into early next week. Showers 
will favor windward areas, except through the afternoon hours 
across leeward locations where clouds and a few showers associated
with sea breezes will be possible. Rainfall accumulations, 
however, will remain limited with the dry air and stable
conditions in place. Although confidence remains low being so far
out into the forecast, a pattern change will be possible through
the latter half of the upcoming week as a front approaches and
moves into the area. 

&&

.DISCUSSION...
The latest surface analysis and satellite imagery showed the 
subtropical ridge located near/just north of the islands 
(southward of its typical position) and the tail-end of a 
dissipated front laying out from east to west within a few hundred
miles north-northeast of the state. Satellite-derived 
precipitable water (PW) imagery depicted a band of higher moisture
along this boundary to the north with values ranging from 1.1-1.3
inches. Drier conditions were shown over the islands with values 
holding around 1-1.2 inches. The latest statewide rainfall 
summary reflected the dry conditions with peak 12-hr totals 
(through 2 am HST this morning) remaining around a tenth of an 
inch or lower. The exception has been over Oahu where peak 
accumulations ranged from a quarter to a little over half of an 
inch (mainly windward areas). 

Guidance remains in decent agreement through the upcoming weekend 
and shows the subtropical ridge remaining in the vicinity of the 
islands as a series of fronts pass to the north. Mostly stable 
conditions will prevail due to the presence of dry air and ridging 
holding aloft. Showers that do develop will favor windward areas,
except through the afternoon hours across some leeward locations 
where clouds and a few showers associated with sea breezes will 
be possible. Rainfall accumulations will remain limited with the 
dry air in place. Background trades will fluctuate in strength 
each day, with the strongest trades expected over the eastern end 
of the island chain. 

Increasing rain chances can't be ruled out Wednesday through
Friday of the upcoming week as the jet dips southward and drives 
a cold front toward the area. Guidance shows southerly winds 
(moderate to breezy Kona winds) and increasing moisture along this
boundary setting up across the islands as it moves through. 
Uncertainty, however, remains high due to recent model 
fluctuations and this being so far out in time. Additional fine 
tuning of the forecast through this period will be likely through 
the upcoming weekend as confidence steadily improves from cycle to
cycle. 

&&

.AVIATION...
Light winds will prevail across the state today and tonight, with
daytime sea breezes and overnight land breezes expected in most 
areas. A few light showers will affect windward areas and 
locations near the coast during the overnight and early morning
hours, and the interior and mountain areas during the afternoon
and early evening hours. Brief MVFR cigs/vsbys will be possible 
in showers, but predominantly VFR conditions are expected 
statewide over the next 24 hours. 

No AIRMETS are currently in effect, and none are expected today.

&&

.MARINE...
A large northwest swell associated with a system that reached 
hurricane-force strength over the past couple of days across the 
far northwest Pacific is expected to fill in this weekend. This 
large and very dangerous swell is slated to reach Kauai early 
Saturday morning, then spread down the island chain the rest of 
Saturday and Saturday night. The swell will peak at around 15 feet
and 18 to 20 seconds Saturday evening, which will translate to 
warning level surf for both north and west facing shores of most 
islands, including the Kona side of the Big Island Saturday 
through Sunday. The swell will drop off to advisory level surf by 
Sunday night. A series of reinforcing swells from the northwest 
and west-northwest, will maintain advisory level surf along north
and west facing shores through the middle of next week. Expect a
downward trend on Thursday.

Due to the low pressure systems passing well to the north, the 
surface ridge has been suppressed south to just north of the 
island chain. This has resulted in a light easterly, or variable 
wind flow. Little change is expected in this pattern through at 
least the first half of next week.

There is currently no marine warnings in effect. But by tonight, 
a High Surf Warning will be hoisted for north and west facing 
shores. Also, a Small Craft Advisory (SCA), for elevated seas at 
or above 10 feet, will be issued for marine zones exposed to this 
large northwest swell.

By Wednesday, the SCA due to elevated seas, will be lowered for 
most, if not all of the marine zones. However, an approaching 
front will tighten the pressure gradient leading to some breezy 
southwest winds, which might require an SCA for waters around 
Kauai County on Wednesday night, running through Thursday. The 
front is expected to drop into the western offshore waters early 
Thursday morning, then push down the island chain the rest of 
Thursday and Thursday night, exiting the far eastern offshore
waters by Friday evening. Breezy northeast winds follow
immediately behind the front, warranting a continuation and or 
issuance of the SCA. 


&&

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Jelsema
MARINE...Lau