Drought in Hawaii, March 19 to 31, 2019

Area Forecast Discussion
National Weather Service Honolulu HI
833 PM HST Mon Mar 18 2019

.SYNOPSIS...
A high pressure system will drift eastward just north of the
Hawaiian Islands, keeping moderate trade winds in the forecast
through Tuesday. Dry stable air aloft will limit shower activity.
On Wednesday, a cold front approaching the islands from the north
will weaken the ridge and produce light winds. High pressure will
build back in over the region from Thursday onward with a cold
front bringing clouds and showers to the islands on Saturday and
Sunday. Stronger trade winds are expected to arrive with the
frontal passage.

&&

.DISCUSSION...
Satellite imagery this evening shows stable stratocumulus clouds
across the region with some clouds banking upstream of each island.
A high confidence for fair weather remains in the local area
forecast through Friday.

A surface high will drift eastward across the Central Pacific
basin tonight with moderate trade winds continuing through
Tuesday. By Wednesday, the surface high moves into the East
Pacific and a broad trough with associated cold front will move
into the Central Pacific. This trough will weaken the ridge north
of the islands producing a light wind regime on Wednesday with
modified sea breezes developing over leeward sections of each
island. Large scale subsidence under the upper level subtropical
ridge will keep a stable layer aloft (trade wind inversion)
capping vertical cloud development to around 6000 feet. Shower
activity will therefore remain isolated through Wednesday.

A stronger surface high will move eastward into the Central
Pacific on Thursday, heralding a return to northeast trade winds
with just a slight increase in windward shower activity. A weak
cold front will drift into the islands from the north reaching
Kauai on Saturday morning. Expect clouds and showers to spread
southeastward across the rest of the state through the weekend.
Model trends from both the American (GFS) and European (ECMWF)
over the last 24 hours are showing a weaker and slower moving
frontal boundary. Cloud heights on model cross sections are now
ranging between 8000 and 10000 feet, roughly 2000 feet lower than
previous operational model runs. However, surface trade winds
remain strong which will tend to focus clouds and showers over
windward and mountain areas of each island through the weekend.

Dry stable air aloft will move in behind the front and breezy
trade winds will stay in the forecast through the first half of
next week. Expect more typical isolated to scattered windward and
mauka showers through the middle of next week with the higher
trends in this range forecast during the overnight and early
morning hours.

&&

.AVIATION...
Tonight, surface high pressure north of the region will bring
light to moderate east northeast flow, veering to easterly by
mid-day Tuesday. Limited shallow moisture may allow for
-SHRA along the windward coasts and slopes. Otherwise,
VFR conditions and partly cloudy skies prevail.

No AIRMETS are current in effect.

&&

.MARINE...
Moderate to locally strong trades will continue tonight, then ease
Tuesday through Wednesday as a front passes by well to the north
of the islands. A Small Craft Advisory (SCA) remains in effect for
all waters through tonight, and this will likely need to be
extended through Tuesday for portions of the marine area due to
elevated seas associated with the current large northwest swell,
with all areas forecast to drop below SCA levels by Tuesday night.
The trades will begin to re-strengthen Wednesday night as a new
high builds northwest of the state, reaching moderate to strong
speeds once again Thursday through the weekend.

Surf along north and west facing shores continues to steadily
decline this evening, but the latest buoy observations continue to
support warning level surf along north and west facing shores. As
a result, the High Surf Warning (HSW) remains in effect for most
north and west facing shores and High Surf Advisory (HSA) remains
in effect for west facing shores of the Big Island through
tonight. Buoys 51001 and 51101 northwest of the state continue to
show a steady decline in swell and should translate to surf
dropping below warning levels from northwest to southeast down the
island chain later tonight.

The active pattern across the northern Pacific will continue
through the week with overlapping long-period northwest swells
expected Wednesday, Friday, and Sunday. The northwest swell Wednesday
and Wednesday night will be the largest of the three, which could
drive the surf close to warning levels around its peak.
Otherwise, the series of swells is expected to keep surf near or
at advisory levels along north and west facing shores Wednesday
through Saturday.

Surf along east facing shores will remain small through midweek,
then rise Friday into the weekend as strong trades return locally
and upstream. Surf along south facing shores will remain small
through the week with mainly background southerly pulses moving
through.

&&

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

High Surf Advisory until 6 AM HST Tuesday for Kona.

Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian
waters-

&&

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Jelsema