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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 200637

Area Forecast Discussion
National Weather Service Honolulu HI
837 PM HST Tue Mar 19 2019

Stable and dry conditions will persist across the islands through
Wednesday night, thanks to a persistent high to our northeast.
Trade winds will increase Thursday and Friday as a cold front
approaches from the northwest. This front will be close enough to
usher in increased clouds and showers across the area Saturday
and Sunday.


High pressure far northeast of the islands, combined with ridging
aloft, will continue to bring drier than normal conditions to the
region tonight. The high is expected to move eastward through
Wednesday and the pressure gradient over the islands will
slacken. This will cause winds to decrease state-wide. By
Thursday, a front will edge closer to the main Hawaiian islands,
tightening the pressure gradient and boosting winds across local
waters once again.

Models show the frontal cloud and shower band reaching Kauai on
Saturday, but not making it much further down the island chain.
Trade winds and moisture are expected to increase along and ahead
of the front. The result will be an increase in rainfall coverage,
favoring windward areas over leeward areas.

Sunday will see surface high pressure building in behind the
front as an upper trough approaches the islands from the west.
Expect windy conditions due to the high, and increased trade
shower activity due to instability provided by the upper trough.
The upper trough is expected to push through the islands by Monday
night, leaving a drier trade wind pattern in its wake.


The high pressure ridge north of the islands will weaken on
Wednesday with lighter winds in the forecast. Expect sea breezes
and interior clouds to develop over each island in the later
morning to afternoon hours.

No AIRMETS are currently in effect or anticipated through this


A brief period with light to moderate trades is expected late
tonight through Wednesday night as the ridge shifts south near the
area due to a front passing to the north. Some areas near the
coasts will experience land and sea breeze conditions during this
period, mostly leeward coasts. A return of fresh to strong trades
is expected Thursday through the weekend as high pressure builds
north of the area. A combination of overlapping north to northwest
swells and wind waves rising from the strengthening trades will
lead to Small Craft Advisory (SCA) conditions over exposed waters
late Thursday through the weekend. Seas may reach advisory levels
over exposed waters Wednesday into Wednesday night due to a large
northwest swell expected to build down the island chain.

Surf along north and west facing shores will remain up through the
weekend as the active pattern across the north Pacific continues.
A series of north to northwest swells is expected with the first
one building down the island chain through the day Wednesday,
likely peaking late Wednesday through Wednesday night. A long-
period reinforcement is expected Friday with its peak Friday night
into Saturday. A similar swell is expected to build down the
island chain Sunday, then gradually ease through Monday. Surf
will climb to and above advisory levels by the end of the day
Wednesday, then likely continue through Sunday. A moderate
northerly swell will be possible next Monday night through Tuesday
that could bring the surf back to around advisory levels for
north facing shores.

Surf along east facing shores will remain small through Thursday,
then rise Friday through the weekend as fresh to strong trades

Surf along south facing shores will remain small each day with
mainly background southerly pulses moving through.






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office