Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Honolulu HI
830 PM HST sun Aug 2 2015

Synopsis...
moderate to fresh trades winds will continue tonight...then decrease
on Monday. Showers will remain focused over windward areas...
especially windward Big Island tonight and Monday. Hurricane
Guillermo is expected to weaken into a tropical storm before
reaching the eastern half of the island chain by early Wednesday
morning. Guillermo will then track west northwest across the rest of
the Aloha state through Thursday. A moderate to locally strong trade
wind flow will return Friday and into the weekend.

&&

Discussion...
one more night of moderate and gusty trades tonight as a low
located just to the SW of the islands continues to migrate west.
Pressure gradients will begin to relax rather quickly on Monday with
the trades becoming light to moderate through Tuesday. Meanwhile...a
broad upper level ridge over the area will keep a mostly dry and
stable airmass in place through late Tuesday. However...abundant
tropical moisture just upstream of The Big Island will keep higher
chances of rain across windward and southeast areas of The Big Island
through late Monday...along with the typical afternoon/early evening
showers over the Kona side.

At 5 PM HST...Hurricane Guillermo was located about 725 miles east-southeast
of Hilo and moving west-northwest at about 10 miles per hour. The hurricane is forecast
to weaken to tropical storm status by the time it approaches The
Big Island sometime Wednesday morning. If Guillermo remains close to the
current forecast trends it should follow a west-northwest track
along the smaller islands on Wednesday and Thursday. And although it is still a
little early to talk about any specific potential wind threat for
the islands...it is very likely that the large field of moisture
associated with Guillermo will bring periods of heavy rain and
potential for significant flooding statewide from late Tuesday through
Thursday. The situation will be evaluated tonight by the Central Pacific
Hurricane Center in Honolulu in order to determine when/where for a
tropical storm watch could be issued.

A hydrologic outlook...see product esfhfo on our website...has been
issued to outline the Middle-Range forecast flood threat. Guillermo
also has the potential to bring windy conditions and thunderstorms.

Once Guillermo clears the area...global models are in fair agreement
in bringing back a more typical trade wind weather regime for the
end of the week.

&&

Aviation...
the moderate to fresh trade winds will gradually decrease tonight
into Monday. Airmet Tango for low level turb over and immediately
south through west of the mountainous terrain will remain posted at
least through the current airmet period. The trend in wind speeds
is decreasing and the airmet will be reevaluated after 10z.

Tropical moisture continues to linger over The Big Island and aide
in the production of enhanced clouds and showers over the windward
areas. Prevailing MVFR with brief IFR is expected through most of
the night along the north through east slopes...including phto. Airmet
Sierra for mountain obscuration remains posted. Expect conditions to
gradually improve after 12z...with the likelihood of lowered
ceilings sticking around through Monday morning. Elsewhere VFR
conditions will prevail...with only localized MVFR in passing
showers.

&&

Marine...
a Small Craft Advisory is in effect through 6 am HST Monday.
Winds and seas are expected to increase again as Hurricane
Guillermo approaches the state. Guillermo should reach the
southeastern offshore waters by Tuesday...possibly at tropical storm
strength...then continue to slowly weaken as it nears the island
chain.

A large east swell from Guillermo will keep high surf advisory
conditions along east facing shores of most islands through Tuesday.
The surf will spread to the western end of the state tonight...peak
Monday night...followed by a gradual decline Tuesday. The effects
of Guillermo will likely boost locally generated wind waves and
surge Tuesday night / Wednesday through Thursday. More specific
details of marine hazards associated with Guillermo would be
determined in the next day if / when we decide to issue watches
and subsequent warnings. Adverse effects for any of the Hawaiian
coastal and offshore waters cannot not be ruled out.



&&

Hfo watches/warnings/advisories...
high surf advisory until 6 PM HST Tuesday for east facing shores
of Kauai Oahu Molokai Maui and The Big Island.

Small Craft Advisory until 6 am HST Monday for Oahu leeward
waters-Kaiwi Channel-Maalaea Bay-Pailolo Channel-Alenuihaha
Channel-Big Island leeward waters-Big Island southeast waters.



&&

$$

Discussion/marine...reynes
aviation...Eaton

National Weather Service Glossary of Abbreviations