690 
FXHW60 PHFO 051354
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
354 AM HST Sun May 5 2019

.SYNOPSIS... 
The cold front that quickly moved down the island chain Saturday
is slowly moving over the Big Island early this morning. This 
boundary combined with a secondary band of showers quickly 
advancing down the island chain will keep the rain chances up 
across the eastern half of the state today. Some showers may be 
heavy at times with gusty winds due to a combination of the front 
and an upper low approaching from the north. Drier and cooler air 
along with gusty northwest winds will fill in today from west to
east, with trade winds unlikely to make a return until later this
week.

&&

.DISCUSSION...
Early morning observations, satellite data and radar trends 
showed the front that quickly moved through the islands Saturday 
now over the Big Island slowly shifting eastward. A secondary 
band of showers associated with a post-frontal trough is quickly 
moving through from west to east approaching Maui County. These 
surface features combined with an anomalously deep upper low 
dropping south into the area will keep the rain chances up across 
the eastern half of the state today. Some showers will be heavy at
times and capable of producing gusty winds up to 45 mph. Guidance
continues to depict the upper low stalling just north of the 
islands today, then drifting east-southeastward through tonight. 
Although a storm or two can't be ruled out over the northern Maui 
County and Big Island windward waters, the better dynamics and 
forcing for ascent will remain positioned just north of these 
waters today. 

Much drier and unseasonably cooler air with gusty northwest winds
will fill in from west to east today through tonight as the front
continues eastward. Temperatures will only manage to hit the mid-
to-upper 70s through the afternoon hours today, then dip into the
low-to-mid 60s tonight into Monday morning for the overnight 
lows. Dewpoints are forecast to drop into the 50s through this 
time due to the drier air. 

As the upper level low fills and lifts off to the northeast through 
the first half of the week, it will leave a weak trough of low 
pressure over and around the state. Light and variable winds will be 
the result each day from late tonight through Wednesday, which 
will give way to a land and sea breeze regime. A return of light 
to moderate trades will become a possibility through the second 
half of the week.

&&

.AVIATION...
A late season cold front passing over the Big Island will 
continue to press se at close to 20 kt. Locally strong south to 
southwest winds are expected along and ahead of the front. AIRMET
Tango is currently in effect for low level turbulence across Maui
and the Big Island downwind of higher terrain or east of the
terrain.

Low ceilings and locally heavy downpours along the front have 
necessitated AIRMET Sierra for mountain obscuration across
Northwest Big Island. Conditions are expected to improve by mid
morning. 

Gusty north to northwest winds are expected to develop across the
smaller islands this morning and the Big Island this afternoon 
once the front pushes off to the east. An AIRMET for low level 
turbulence to the south and east of higher terrain of the smaller 
islands may become necessary later this morning. 

&&

.MARINE...
A cold front in the vicinity of the Big Island early this morning,
will shift eastward, exiting to the east of the coastal waters by
this evening. Strong and gusty west-southwest winds are expected 
in advance of the front, with strong and gusty west-northwest 
winds expected behind the front. As a result, a Small Craft 
Advisory (SCA) remains in effect for the entire marine area 
through through 6 PM this evening. Winds are expected to trend 
downward fairly rapidly from northwest to southeast down the
island chain tonight and Monday as an area of low pressure north 
of the islands weakens. This area of low pressure will continue to
weaken into a surface trough by the middle of the week, then 
shift west of the coastal waters on Thursday. As a result, light 
and variable winds are expected across the marine area Monday
night through Wednesday, with overnight land breezes and daytime 
sea breezes expected near the coast. Light trade winds should 
begin to fill back in on Thursday, with light to moderate trades 
then holding in place through next weekend. Winds and seas are 
expected to remain below SCA levels tonight through next weekend.

A moderate-sized, rough and short-period northwest swell will
continue to affect the island chain today through Monday, with 
surf expected to remain below advisory levels as the swell peaks 
late this afternoon or this evening. Otherwise, a few small 
swells will maintain small surf along north, west, and south 
shores through mid-week. A more significant south swell is 
possible by the end of the week, which could push south shore surf
up to near advisory levels. See the Oahu Surf Discussion (SRDHFO)
for details on the swell sources.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 PM HST this evening for Big Island 
Summits.

Wind Advisory until 6 PM HST this evening for Haleakala Summit.

Small Craft Advisory until 6 PM HST this evening for all 
Hawaiian waters-

&&

$$

DISCUSSION...Gibbs
AVIATION...Bedal
MARINE...Jelsema