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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 181331
Area Forecast Discussion
National Weather Service Honolulu HI
331 AM HST Thu Apr 18 2019
A surface ridge will remain north of the islands through the
coming week. A trough aloft will move away to the east by tonight
as a ridge aloft builds over the area.
The 2 AM surface analysis shows a 1024 mb surface high about 800
miles north of the islands near 33N163W. The high is forecast to
move northeast and strengthen through tomorrow, then remain nearly
stationary through early next week. A ridge extending southwest
from the high will remain north of the main Hawaiian Islands and
maintain locally breezy trade winds over the islands.
As of 3 AM, satellite loops and surface observations show partly
cloudy skies over Kauai. Skies are mostly cloudy over windward
areas of the other islands with mostly clear skies over leeward
areas. Radars show scattered showers moving west over windward
areas of the Big Island, Maui, Molokai and Oahu with mostly dry
conditions elsewhere. Little change is expected for the next few
The trough aloft will move away to the east tonight and a ridge
aloft will persist over the area through early next week. Locally
breezy trade winds will continue over the islands. The trades will
carry scattered showers over windward areas, mainly during the
night and early morning hours. Afternoon heating will produce
clouds and showers over leeward slopes of the Big Island and Maui.
Otherwise, leeward areas will remain mostly dry.
Clouds and showers increased during the overnight hours., but Kauai
has stayed dry, and will remain mostly dry through today. The
other islandsare having scattered showers, favoring the windward
and mountain areas, with a few of these showers moving briefly
into the lee areas of Maui and Oahu. These showers should be
waning as we head further into the morning. The area of showers
east of the Big island, also, no longer poses a threat to that
island. Current maximum cloud tops are around 13k feet, otherwise
they are around 10k feet.
Trades will continue to strengthen as the day progresses. AIRMET
Tango, already in effect for mechanical turbulence below 8k feet,
will continue until further notice, as a ridge of high pressure
hold steady north of the area for at least the next couple of days.
Fresh to strong easterly trade winds associated with a strengthening
ridge north of the islands will fill in today and continue
through early next week. A small craft advisory has been issued
for the Pailolo and Alenuihaha channels, Maalaea Bay, and over the
waters around South Point of the Big Island through Sunday where
the strong winds are expected.
Surf along north and west facing shores will remain small today,
then rise tonight into Friday as a new north-northwest (320-340
deg) swell builds down the island chain. This source will be from
a gale that was centered over the Aleutians near the Date Line
Sunday that quickly tracked south-southeast and weakened Monday
through Tuesday. After the peak on Friday, the swell will quickly
ease Friday night into the weekend. A small westerly swell from a
compact gale that has developed east of Japan will be possible
early next week.
Surf along south facing shores will remain small through the weekend
with mainly background south-southwest pulses moving through. An
upward trend is anticipated early next week, beginning as early as
Sunday night due to activity south to southeast of New Zealand over
the past few days. Guidance depicts this source peaking at Pago Pago
Saturday, which should correlate to above average south shore surf
continuing into midweek.
Surf along east facing shores will remain small today, then
rise slightly Friday through the weekend due to fresh trades
locally and just upstream. Expect this trend to continue early
Small Craft Advisory until 6 PM Sunday for Maalaea Bay, the
Pailolo and Alenuihaha channels and waters south of the Big
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office