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Hawaiian Islands Synoptic Discussion and Guidance

538
FXHW60 PHFO 181409
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Sun Nov 18 2018

.SYNOPSIS...
Patches of showery clouds will eventually exit south of all islands
late today. Clouds and showers carried by the breezy to locally
strong trade winds will affect mainly windward areas, and may reach
the lee areas of the smaller islands. Drier but still breezy trade
wind weather is expected Monday through Wednesday, with lighter
winds and increased showers possible by Thanksgiving.

&&

.DISCUSSION...
Showery clouds continue to affect windward areas of most of the
islands early this morning, with windward Big Island seeing the most
precipitation while windward Kauai the least. Not surprising
consider an upper level trough is present in the island vicinity,
with its northeast-southwest oriented axis just south of Kauai, as
revealed by satellite water vapor imagery. Meanwhile, moisture from
the tail end of a frontal boundary continues to linger in the island
vicinity, with the bulk of it near the Big Island. As such, early
morning Kauai sounding continued to present a rather dry and
somewhat stable airmass while it is still moist and unstable on
the early morning Hilo sounding. A weakening surface high pressure
north of the state will be providing the breezy trades to the
islands today. Still expect the lingering moisture to slowly shift
south through rest of the day. Moreover, the upper level trough in
the area will also slowly weaken. Thus expect slow improving weather
conditions, with less showers later this morning for windward Oahu
then windward Maui County, while windward Big Island will probably
see some clearing late tonight.

The current weakening high pressure will be replaced by a stronger
high further north of the area tonight through the next few days.
Therefore, winds will remain breezy across the area. Forecast
solutions still indicate less moisture will be in the island
vicinity, under a more stable airmass. Therefore, expect drier but
still breezy trade wind weather Monday through Wednesday.

Latest forecast charts still hinted another moisture band may
reach the islands late Wednesday into Thanksgiving Day. Thus expect
a possible increase in showers for the state by then. Both long
range models are in pretty good agreement upon a trough developing
northwest of the islands toward later part of the week, then passes
north of the state by Friday. As a result, winds will veer and
weaken late on Thanksgiving day into Friday. There is still
some disparity between models on how much moisture the islands will
see, with GFS being the more moist solution.

&&

.AVIATION...
A strong high pressure system will track across the Central Pacific
basin through the middle of next week, maintaining breezy trade
winds across the Hawaiian Islands. Drier air has moved into the
northern islands this morning with more persistent VFR conditions
developing over Kauai, Oahu and Molokai this morning. A weakening
cold front will continue to bring periods of low clouds and rain
showers into the Maui and Hawaii Counties with the trade wind flow
through Sunday afternoon. Periods of MVFR/IFR conditions will linger
over windward and mountain areas of Maui and Hawaii Counties this
morning with low cloud ceilings and showers expected through the
morning over Maui and into the afternoon over the Big Island of
Hawaii. AIRMET Sierra for Mountain Obscuration remains in effect for
north through east sections of Molokai, Maui and the Big Island
today.

AIRMET Tango remains in effect for moderate turbulence across all
islands. Breezy trade winds will cause lower level mountain wave
turbulence over and immediately south through west of mountains on
all islands from SFC-080 for the next few days. An upper level
subtropical jet stream will also produce moderate turbulence aloft
between FL200-350 lasting through the afternoon hours.

&&

.MARINE...
Fresh to strong trade winds are forecast to hold through the middle
of this week, as high pressure builds north of the state in the wake
of a dissipating front pushing south across the eastern islands. A
Small Craft Advisory (SCA) will remain up today across most waters
due to the combination of winds and seas, with the north swell
lingering longer than forecast by Wavewatch. Thereafter, the SCA has
been extended through Tuesday across the typically windy zones
around Maui County and the Big Island, and SCA conditions will
probably continue beyond that time. Surf along east facing shores
will rise today through Wednesday night as the trades strengthen,
though the surf should remain just below advisory levels.

The current north swell will continue to slowly fade today. A
moderate reinforcement out of the northwest is expected to fill in
late Monday, peak Monday night into Tuesday, then fade through
midweek. Surf should remain below the advisory levels along north
and west facing shores with this swell. Small surf will continue
along south facing shores with mainly background southern Pacific
pulses moving through.

&&

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

Small Craft Advisory until 6 PM HST this evening for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai
Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Big Island Windward Waters.

&&

$$

Hui/Jacobson/Bohlin

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