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Temp-1.9 C
RH96 %
WindENE 13 mph
RoadClosed
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Hawaiian Islands Synoptic Discussion and Guidance

947
FXHW60 PHFO 230150
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST Mon Jan 22 2018

.SYNOPSIS...
Trade winds will continue with clouds and showers focused over
the windward sides of the islands overnight. An upper level
disturbance could enhance shower activity through midweek. Some of
the layered clouds over and near the Big Island could spark a
thunderstorm or two, and could even bring some snow or freezing
rain to the summits overnight. Lighter winds with land and sea
breezes are forecast during the second half of the week.

&&

.DISCUSSION...
No significant changes to the forecast philosophy today, so little
change in the forecast. Have lowered day time temperatures at the
Big Island Summits tomorrow by a few degrees. And have added
isolated thunderstorms to some of the Maui and Big Island windward
waters where we saw some development earlier today. This also
coincides with an area of colder temperatures aloft and increased
moisture in the models which indicate the possibility for a
thunderstorm or two overnight. This area lifts off to the east
late tonight and tomorrow.

The forecast for tonight at the summits continues with scattered
showers, which could include snow and freezing drizzle. Clouds
over the summits today brought rain, and with temperatures
hovering around freezing, some of it was freezing rain. While
there are plenty of clouds and showers around, the moisture layer
is not deep enough over the summits to support snow for any length
of time, so any additional snow amounts are expected to be
minimal, except if a thunderstorm were to develop. With confidence
dropping tonight, have cancelled the Winter Weather Advisory.

The morning surface analysis shows a weakening stationary front
about 200 miles north of Kauai. The western edge of the surface
ridge is about 550 miles northeast of Oahu, with a low level trade
flow continuing over the islands. Models show an upper level
trough over the western end of the state, also noted in water
vapor imagery, which is forecast to remain nearly stationary over
the next couple of days. This will help

The afternoon sounding from Hilo experienced some technical
difficulties with the relative humidity sensor, so we are lacking
most of that sounding information. The Lihue sounding shows a more
stable environment with an inversion around 6000 feet and
precipitable water around 1 inch.

The trade wind flow is expected to break down and turn
southeasterly as we head into mid week as the ridge moves to the
east. As winds weaken, some local land and sea breezes will set up
with clouds and showers more likely over interior locations during
the afternoon, and some clearing overnight.

&&

.AVIATION...
An area of clouds and showers continues to affect most areas of
the Big Island and appears to be spreading westward toward the
smaller islands. Except for Hilo, the terminal will be
predominantly VFR.

AIRMET Sierra is in effect for mountain obscuration across
windward sections of the Big Island. These conditions are
expected to persist through the night. The mountain obscuration
AIRMET may be needed this evening for leeward sections of the Big
Island. Additionally, the AIRMET may need to be expanded to
include windward sections of the smaller islands this evening.

AIRMET Tango remains in effect for moderate low level turbulence
over and downwind of the terrain of all islands. The AIRMET is
expected to remain in place through through tonight.

AIRMET ZULU is in effect for light icing in clouds around the Big
Island from 12000 to 20000 feet. This AIRMET will likely be
continued through tonight.

&&

.MARINE...
Current reports indicate current and expected sea state is on
track with previous forecasts and no updates were made to forecast
swells. Forecast changes involved bumping winds up slightly
through early Wednesday in line with the latest model guidance and
observation trends.

A Small Craft Advisory remains posted for most Hawaiian coastal
waters. This is due to several factors including a moderate east
swell, increasingly windy conditions, especially around Maui
County and The Big Island, and a moderate size northwest swell
bringing combined seas over 10 feet. These conditions are
expected to continue through Tuesday afternoon. The northwest
swell will gradually lower later on Tuesday so the Small Craft
Advisory may be lowered over some of these exposed waters.
With trade winds anticipated to remain fresh to strong Tuesday
into early Wednesday, the advisory over the typically windier
waters may need to be extended there.

A High Surf Advisory is posted for most north and east facing
shores and for west facing shores from Molokai westward. The
current east swell will continue to produce hazardous surf along
east facing shores with the largest waves expected over the east
end of the island chain. The new moderate size northwest swell
will produce advisory level surf along exposed shorelines through
Tuesday with the largest waves expected over the west end of the
island chain. There will also be a small south swell affecting
exposed shorelines through Tuesday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Tuesday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala-South Big Island-Big Island North and East.

Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

&&

$$


DISCUSSION...M Ballard
AVIATION...Powell
MARINE...Brenchley

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