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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 271402
Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST MON JUN 27 2016
High pressure far north of the state will maintain moderate to
breezy trades through the week. Clouds and passing showers will
favor windward and mauka areas, with mainly dry conditions leeward.
The Kona slopes on the Big Island will continue to see clouds and
widely scattered showers each afternoon and evening, followed by
clearing skies each night and morning. Wetter trade wind weather is
possible Wednesday and Thursday.
Breezy trade winds continue early this morning with passing showers
affecting mainly windward areas at times. The surface high pressure
system that is providing the winds will remain pretty much in place
for the next couple of days. Early morning Lihue sounding depicted a
trade wind profile, with low level moisture extending to near 8
thousand feet in a mostly stable airmass while Hilo sounding is
marred by sensor wetting. Latest satellite imagery revealed there
are more low clouds upstream east of the islands. These clouds will
pass the state throughout the day, providing more showers affecting
mainly windward areas. There are also some high clouds passing over
the state, keeping skies cloudier at times. Mainly fair weather will
continue over lee areas of most of the islands, while lee area of
the Big Island will become cloudy as daytime convection develops
Trade wind weather will reign across the state this week as surface
high pressure stays far north of the area. There will be variations
to this main weather theme though, as forecast models continue to
show a change in the upper level pattern in the coming days. By late
Tuesday to early Wednesday, an upper level trough is forecast to
develop just northwest of the islands, then linger at least through
Thursday. This upper level feature will bring colder air aloft,
resulting in the airmass over the islands becoming more unstable.
Low clouds will be enhanced under the more favorable atmospheric
conditions, increasing the potential for enhanced showers and
even possible thunderstorm development on Wednesday and Thursday.
Furthermore, trade winds may ease slightly on Wednesday as the
surface high pressure far north is forecast to weaken.
Trade winds is forecast strengthen rather strongly with possible
drier trade wind weather for the weekend. A strong surface high is
expected to rebuild far north-northeast of the state, bringing tight
pressure gradient across the area. Forecast models also depicted a
much drier airmass spreading to the state from the east. This will
probably lead a decrease in clouds and showers for the state.
Brief MVFR cigs/vsbys will be possible in passing SHRA in windward
locales, with PHTO the most likely TAF site to be impacted.
Elsewhere, predominantly VFR conditions are expected through the TAF
Airmet TANGO is in effect for mechanical turbulence immediately
south through west of mountains on all islands below 8000 feet.
Airmet SIERRA is also in effect for occasional mountain obscuration
above 2500 feet across north and east sections of the Big Island.
A small craft advisory remains in effect for the typical coastal
waters in Maui county and the Big Island vicinity today due to the
locally strong trade winds. This advisory may be extended again if
the winds hold tonight and Tuesday. Winds may drop enough briefly
for conditions to improve by late Tuesday and Wednesday. But then,
as the trades are forecast to ramp up rather strongly toward the
weekend, small craft wind conditions are posed to return to the
coastal waters with an increase in the area.
A southerly swell will slowly peak through Tuesday, while a
south-southeast swell is expected to arrive Wednesday, persisting
through rest of the week. Both swells are expected to bring below
advisory level surf along south facing shores. The short-period
trade wind swell will continue and may further increase a bit toward
the weekend due to the strengthening trades, possibly bringing
advisory level surf along east facing shores.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office