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Hawaiian Islands Synoptic Discussion and Guidance

773
FXHW60 PHFO 200614
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
814 PM HST Fri Apr 19 2019

.SYNOPSIS...
Seasonal trade wind conditions will prevail through the weekend and
much of next week as high pressure remains in place to the north.
Clouds and showers will favor the typical windward locations each
day.

&&

.DISCUSSION...
The latest surface analysis showed a 1029 mb area of high pressure
centered over the northeast Pacific and a ridge extending west-
southwest from it to an area north of the islands. Water vapor
imagery showed a ridge positioned over the region and mostly dry air
aloft. Satellite and the afternoon upper air soundings showed
moisture levels near to slightly below normal for this time of year
and a strong subsidence inversion between six and eight thousand
feet. Rain gages support the dry conditions with minimal
accumulations measured over the past 12-hrs (through 6 PM HST). Peak
totals for this period have been on the Big Island along the
windward coast from Hamakua to North Kohala (.25 to .88 inches).

Guidance supports the mostly dry and stable trade wind pattern to
continue through much of next week. Trades may trend up over the
weekend due to the ridge strengthening north of the islands. Breezy
conditions will result, especially through the late morning and
afternoon hours. The upper ridge is forecast to remain over the
region into next week with mostly dry mid- to upper-level air
holding in place. These upper conditions combined with a strong
subsidence inversion will limit the rainfall potential/coverage,
even for windward locations. The exception will be due to pockets of
higher moisture moving through periodically within the trades, which
will translate to better windward rainfall coverage.

For the extended period, guidance depicts lowering upper heights and
the ridge to the north weakening due to a weak shortwave trough and
surface front moving into the region late next week. Forecast
confidence this far out remains low, but if this scenario does
evolve, trades would trend down, potentially becoming light and
variable for some locations.

&&

.AVIATION...
A high pressure ridge north of the state will keep the islands in
a moderate to breezy trade wind weather pattern through the
weekend. Near surface wind speeds are strong enough to support
moderate low level turbulence over and south through west of
mountain ranges of all islands. Scattered shower activity will
favor windward and mountain sections with brief periods of MVFR
conditions mainly during the overnight hours.

AIRMET Tango remains in effect for tempo moderate turbulence below
080. This AIRMET will likely remain in effect through the
weekend.

&&

.MARINE...
A ridge north of the islands will maintain the fresh to strong
trades into early next week. The Small Craft Advisory (SCA)
will continue at least into early next week for the typical
windier areas near Maui County and the Big Island. Anticipating a
bit of an uptick in the trades Saturday, so the SCA was expanded
earlier to include windward coastal zones near Maui and the Big
Island as well as the Kaiwi Channel for Saturday and Saturday
night.

Surf along all shores is expected to remain below advisory levels
for the next week. The current north-northwest swell is on the
decline, and is expected to continue declining through the
weekend. A small, west-northwest swell is possible early next
week. Background south-southwest swells will keep surf small along
south facing shores through the weekend. An upward trend is
possible early next week, due to recent activity southeast of New
Zealand. Surf along east facing shores could see a bump over the
weekend with an uptick in the trades. See the latest Oahu Surf
Discussion (SRDHFO) for additional details on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory from 6 AM Saturday to 6 AM HST Sunday for
Kaiwi Channel-Maui County Windward Waters-Big Island Windward
Waters.

&&

$$

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...M Ballard

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



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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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