Flash Flood and Heavy Rain in Hawaii, March 2 to 5, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Mon Mar 2 2020

.SYNOPSIS...
Breezy trade winds can be expected through tonight thanks to
strong high pressure far north northeast of the state. Clouds and
passing showers will favor windward and mauka areas with less
shower activity over leeward locations. The high will weaken
Tuesday and Wednesday with lighter trade winds expected. A new
strong high will build in far north of the area Thursday through
Saturday with trade winds strengthening once again. Passing showers
will tend to favor windward and mauka areas and be highly dependent
on incoming moisture availability.
&&

.DISCUSSION...
A strong 1040 mb high is centered far north northeast of the
area. This is resulting in breezy to locally windy trade winds
across the state. Meanwhile, an upper level low is centered a
couple of hundred miles north of the Big Island. The airmass
remains a bit on the unstable side. Moisture embedded in the
trades is providing for passing showers across the area especially
for windward and mauka areas. Some showers may be briefly
moderate in intensity.

The surface high is forecast to remain nearly stationary and
weaken over the next couple of days. This will allow for a gradual
diminishing of trade wind speeds across the area. Meanwhile, the
upper level low will drift northwest and weaken allowing for a
more stable airmass to be in place across the area. Some passing
showers will however continue to fall over windward and mauka area
at times with a few showers still possible over select leeward
locations.

Trade winds will diminish even more on Wednesday as a frontal
system passes by far north of the state. Some sheltered areas may
see some daytime sea breezes but overall the flow will still
resemble easterly trades. Some passing light showers will remain
in the forecast mainly for windward and mauka areas.

A new strong high will build in north of the area Thursday and
Friday with trade wind speeds gradually ramping back up to breezy
to locally windy levels by the weekend. Showers will continue to
favor windward and mauka areas with the winds sufficiently strong
enough to blow some showers over to leeward areas at times. Shower
frequency will be high dependent on incoming moisture
availability

&&

.AVIATION...
Strong trades will begin to trend down overnight as a high
pressure system north of the state begins to weaken. Until wind
speeds decrease, will leave AIRMET Tango for low level turbulence
downwind of terrain for all islands. Additionally, AIRMET Tango
for tempo moderate turbulence between FL180 and FL300 remains in
effect.

Clouds and showers will hold on through the day, particularly for
windward locales where AIRMET Sierra for mountain obscuration
remains in effect for all islands except the Big Island. However,
because the trades remain strong, showers may impact leeward areas
at times. MVFR conditions are possible with any of these heavier
showers. As the upper level low responsible for these clouds and
showers begins to weaken and move away from the island chain,
conditions are expected to improve for Tuesday.

&&

.MARINE...
A strong surface high will remain centered well northeast of the
islands through the first half of the work week, while a weak
surface trough shifts eastward just to the north of the state.
This will keep the tightest pressure gradient, and strongest
winds, north of the coastal waters. The trades will trend downward
through tonight, with moderate to breezy trades expected in most
areas Tuesday through Wednesday night. The weak surface trough
will dissipate Thursday, while a new strong surface high builds to
the north of the island chain. This will result in strengthening
trade winds during the latter half of the work week, with strong
to near-gale force trades expected Friday through the weekend.

A Small Craft Advisory (SCA) remains in effect for all waters
through tonight. Winds and seas will trend downward tonight
through mid week, with some marine zones dropping out of the SCA.
Other marine zones exposed to lingering trade wind swell will
likely hold onto SCA level seas through Tuesday and possibly into
Tuesday night. Conditions should fall below SCA thresholds across
the entire marine area Wednesday and Wednesday night. Winds and
seas will then trend up Thursday, with SCAs likely being required
for most, if not all waters, by Friday and continuing through the
weekend.

The persistent strong trade winds over and upstream of the
islands will keep advisory level surf in place along east facing
shores through at least Tuesday, and possibly right through mid
week. East shore surf will trend downward Wednesday night and
Thursday, before rising back close to advisory levels once again
Friday night into the weekend.

Surf along north and west facing shores will remain very small
through the week and into the weekend, although some wrap from
trade wind swell is expected through Tuesday. Surf along south
facing shores will remain small with mainly background south and
southwesterly swells moving through.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Tuesday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-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-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-
Big Island Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory until 6 AM HST Tuesday for Oahu Leeward
Waters-Maui County Leeward Waters-Maalaea Bay.

&&

DISCUSSION...Burke
AVIATION...Dye
MARINE...Kinel