Wildfire in Hawaii, March 11, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
1006 AM HST Sun Mar 11 2018

.SYNOPSIS...
Strong high pressure centered far to the northwest of the state
will maintain a rather cool and dry airmass, along with fresh to
strong trade winds today. A weak front is forecast to move across
the area tonight and Monday accompanied by a increase in windward
and mauka showers. Thick, high clouds will blanket most of the
state through the next several days, along with breezy winds
continuing. A wetter weather pattern is on tap for much of this
week as tropical moisture moves over the area.

&&

.DISCUSSION...
A strong high pressure system currently northwest of the state
will maintain a rather cool and dry airmass, along with fresh to
strong trade winds, through at least the middle of this week.
Radar shows light showers embedded in low level flow providing
isolated windward and mauka showers. The subtropical jet over
Hawaii is pushing broken to overcast high clouds over the area.
A shallow cold front is forecast to move across the island chain
late today and into Monday. A slight uptick in shower activity
will accompany the front that will mainly affect windward slopes.

A broad upper trough is forecast to take up a position just to
the west southwest of the main Hawaiian Islands tonight.
Southerly flow on the east side of this trough will draw up deep
tropical moisture and increase the chances for rain across
portions of the state beginning Monday. The high clouds will
thicken up and keep overcast skies over the state through Thursday.

Models indicate that the initial surge of moisture will affect The
Big Island and Maui beginning late Monday, with rainfall chances
increasing for the rest of the island chain by midweek. However,
inconsistencies persist in the models on the placement of the
highest rain threat areas as well as the structure of local winds
due to changing depictions of a surface trough or closed low
forming south of the state. Wetter weather is coming, but
confidence remains rather low as to when and where the greatest
amounts of rain will fall. This wetter weather pattern is forecast
to linger over the area through at least Thursday.

&&

.AVIATION...
High pressure northwest of the state will keep fresh to strong trade
wind flow in place through Monday. Clouds and showers will favor
windward and mauka areas, with some brief MVFR cigs/vsbys possible
in these areas. Predominantly VFR conditions are expected at the
TAF sites through 18Z Monday. Conditions are expected to
deteriorate particularly in windward areas during the day on
Monday.

AIRMET Tango is in effect for moderate low level turbulence over
and downwind of the terrain of all islands. These conditions will
likely remain in place through at least Monday. AIRMET Tango is
also in effect for moderate upper level turbulence between FL200
and FL400. Conditions are expected to continue through the day
today, but may improve tonight.

Light icing has been added to AIRMET Zulu from Oahu to the Big
Island due to the thickening mid and upper level cloud cover.
The mention of light icing may need to be expanded to include
Kauai later today or tonight. Conditions are expected to remain
below the AIRMET threshold for moderate icing through the day
today. AIRMET Zulu may be needed for moderate icing across
portions of the state tonight.

&&

.MARINE...
Fresh to strong northeasterly trade winds will persist through
the weekend as the islands remain under the influence of a strong
surface high located far northwest of Kauai and a deep trough far
north-northeast of the state. A Small Craft Advisory (SCA) remains
in effect for the typically windier waters around the Big Island
and Maui County., and will be expanded to all waters tonight.

A large north swell will fill in late today. The north swell is
being generated by a captured fetch of gale force winds between
the above mentioned high and the deep trough to the north-
northeast. The north swell will arrive this afternoon, and north
shore surf from Kauai to Maui will build to advisory levels this
evening, then peak possibly up to low end warning levels by
Monday. During this time, advisory level surf is expected along
east facing shores, including the Big Island. Thus, a High Surf
Advisory (HSA) will go into effect tonight for north and east
facing shores of most islands. The north swell will quickly
decline Tuesday and Wednesday, as a rough, short- period trade
wind swell builds. As a result, a High Surf Advisory should remain
in place for east facing shores through Tuesday or Wednesday.

The current SCA for the typically windy waters around the Big
Island and Maui County will be expanded to cover all waters by
this evening. Tonight and Monday, trade winds will increase as a
developing trough south of the state tightens the local pressure
gradient, and the incoming north swell will push combined seas
above 10 feet. As the north swell drops, the strong trades will
generate large and rough short period seas, which will likely keep
the SCA in place through at least Tuesday. In addition, the
trough moving up from the south will bring the potential for
unsettled weather through mid week. Mariners should monitor the
latest forecast as the weather pattern becomes better defined.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory from 6 PM this evening to 6 PM HST Monday for
north and east facing shores of Niihau, Kauai, Oahu, Molokai, Maui
and the Big Island.

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 from 6 PM this evening to 6 PM HST Tuesday
for all remaining coastal waters.

&&

DISCUSSION...Foster
AVIATION...Jelsema
MARINE...Morrison