High Surf Advisory 48, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
821 PM HST Tue Nov 1 2016

.SYNOPSIS...
A surface ridge north of the state will drive stable weather with
breezy trade winds into this weekend, with only slight deviations
in wind speeds and moisture levels. Clouds and showers will be
limited, but focus over the windward slopes. A weak front may
approach the state from the north on Monday.

&&

.DISCUSSION...
Dry conditions prevail across most of the Aloha State on this
Tuesday evening. Showers have increased during the early evening
across the windward slopes of Haleakala and the Hamakua coast,
and infrared satellite imagery shows an area of overcast low
clouds stacked up over the adjacent windward waters. Further to
the west, just scattered clouds and isolated showers are present
even over the windward areas from Molokai through Kauai, while
mostly clear skies prevail over leeward sections. Rain gauges
report light amounts of a quarter inch or less at some windward
locations on Maui and the Big Island, with dry conditions
elsewhere. Surface analysis depicts a 1029 mb high centered about
900 miles northwest of Kauai, with breezy trade winds prevailing
over the islands within a fairly tight pressure gradient to the
southeast of this high. Aloft, a weak and positively-tilted upper
trough remains over the eastern part of the state, with associated
high clouds shifting east of the Big Island during the early
evening. A strong mid/upper level ridge is centered just west of
Midway, and continues to provide stable conditions over the state.
MIMIC-TPW imagery shows a dry airmass over and upwind of the
islands with estimated PW values near or below one inch. This is
confirmed by the 00Z soundings, which measured PW ranging from
0.82 to 1.01 inches, and found trade wind inversions based between
5500 and 6500 feet.

Overnight, showers will be most common across windward sections
of East Maui and the Big Island, and have updated the forecasts to
increase rain chances a bit for those areas. Otherwise, expect
partly cloudy skies with widely scattered passing showers
windward, and mostly clear and dry conditions leeward.

Little change is expected through the rest of this week and into
the weekend, with a breezy and rather dry trade wind pattern
continuing. Only minor fluctuations in wind speeds and moisture
levels are expected. Showers will focus over the windward slopes
and will be most prevalent during the night and early morning
hours. Leeward areas should stay mostly dry, with a few showers
possible over the Kona slopes during the afternoons.

Longer range models indicate that trade winds will decrease over
the islands on Sunday into early Monday, as a weak front moves
southward over the Central Pacific. This front may reach Kauai by
late Monday, then sag southward across the other islands while
dissipating Monday night into Tuesday. At this time we expect
nothing more than increasing mainly windward showers, with some
showers possibly spilling over into leeward areas.

&&

.AVIATION...
Strong high pressure to the far northwest of state will continue
to promote breezy northeast trade winds through twenty four hours
and beyond. Patchy clouds and showers will favor windward and
mountain locations. With the exception of brief MVFR CIG/VIS in
showers, VFR conditions will prevail all areas.

AIRMET Tango remains in place across the Hawaiian Islands for
moderate low-level turbulence downwind of the mountains.
Conditions are expected to persist through 24 hours and possibly
beyond.

Moderate upper level turbulence is expected over the Big Island
through the remainder of tonight. Conditions are expected to
improve towards morning as the area of strong high level winds
pushes southeast of the state.

&&

.MARINE...
The Tuesday morning ASCAT pass found large areas of 25-30 kt
winds in the Alenuihaha Channel and south of the Big Island. More
recent land-based mesonet data support continued Small Craft
Advisory (SCA) conditions in many marine zones around Maui County
and the Big Island. Trade winds are forecast to decrease slightly
on Wednesday, with the advisory area reduced to the typically
windy zones around Maui County and the Big Island by that time.
SCA winds will likely continue in those zones through the rest of
the week as moderate to fresh trade winds continue.

Beach observations from Tuesday showed that surf along east
facing shores did decrease below advisory levels as expected,
and this surf will continue to slowly decline through Wednesday.
A moderate northwest swell arriving tonight will be reinforced
Wednesday evening and again Thursday night by a pair of large
north-northwest swells. Resulting north shore surf will be well
above advisory levels from late Wednesday through Friday,
possibly peaking at low-end warning levels Wednesday night into
Thursday morning. This swell will gradually decline during the
weekend with surf eventually dropping back below advisory levels.
An even larger north-northwest swell is possible early next week.

&&

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

Small Craft Advisory until 6 AM HST Wednesday for Kaiwi Channel-
Maui County Windward Waters.

&&

DISCUSSION/MARINE...Jacobson
AVIATION...Bedal