FXHW60 PHFO 051949
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Tue Mar 5 2024

.SYNOPSIS...
A wet trade wind pattern with isolated thunderstorms and locally
heavy rain, especially over windward areas, will prevail through
Wednesday night. Breezy trades will further strengthen during the
middle part of the week.

&&

.DISCUSSION...

Split flow pattern over the North Pacific Basin persists with the
northern with ridging in the northern branch maintaining high
pressure along and north of 30N. Low amplitude troughing within the
southern branch lingers over the islands and is the source of the
occasional wave of larger scale forcing over the area. Meanwhile, a
reservoir of rich low to mid level moisture remains positioned
near/southeast of the island chain giving trade winds a source of
enhanced moisture. Together, this spells a period of wet trades for
the islands that began early this week and will persist through at
least Wednesday night.

For this morning, a pocket of moderate to locally heavy showers is
working across Kauai and Oahu while the eastern end of the state
remains mostly clear beneath patchy high clouds and is receiving
only limited windward shower activity. Conditions will improve as
deeper moisture exits to the west this morning with only isolated to
scattered showers expected over windward and mauka zones for the
remainder of the daytime hours. In all likelihood, the wet spot by
this afternoon will be leeward Big Island which featured a decent
convective response beneath extensive high clouds yesterday.
Diminishing high clouds through today should allow greater
instability to develop which will in turn favor a better response
than yesterday. Given the moisture rich airmass in place over the
Big Island, flooding issues are not out of the question should
showers develop sufficiently downslope to cause issues. This will be
the primary focus of attention this afternoon.

By tonight, the center of the resident upper low will be positioned
directly overhead tonight giving the next wave of moisture some
added instability and steeper lapse rates to work with as 500mb
temperatures fall further to around -17C (west) and -14C (east).
Little change in the forecast tonight through Wednesday night as
global model consensus remains strong that the bulk of organized
rainfall will focus over the eastern end of the state, mainly during
overnight periods. Locally heavy rain including isolated
thunderstorms will nonetheless be possible for all windward and
mauka areas.

Heading into the second half of the week (Thursday onward), the
large scale pattern undergoes little in the way of change, but
deeper troughing west of the islands is modeled to pump up heights
locally which should help bring an end to the current wet trade wind
pattern. A more typical breezy to locally strong trade wind pattern
then prevails heading into the weekend.
&&

.AVIATION...

Moderate to breezy trade winds will persist for the next several
days as strong surface high pressure holds north of the state.
Clouds and showers will favor windward slopes and coasts. Periods of
MVFR conditions with low ceilings and visibility in showers are
expected mainly over windward airfields, especially in the late
night and morning hours.

A deepening upper level trough will enhance convective activity.
There is a slight chance of thunderstorms statewide through forty-
eight hours and possibly beyond.

AIRMET Sierra is in effect for northeast facing slopes of Kauai.
Conditions have improved elsewhere and thus the AIRMET was
canceled.

AIRMET Tango is in effect for moderate leeward mountain wave
turbulence over all islands due to breezy trade winds, and is
expected to remain necessary through twenty-four hours and
possibly beyond.


&&

.MARINE...

A strong ~1032 mb high about 900 nm N of the islands will move
slowly E the next couple of days, supporting strong to near-gale
force ENE trade winds. Another high will build N of the islands
toward the end of the week, with little change in wind speeds
expected through the weekend. A Small Craft Advisory is in effect
for all waters, and will likely remain in place through the week.
A persistent trough aloft will keep the island atmosphere unstable
the next couple of days, with briefly heavy, fast-moving showers
producing periods of strong wind gusts and low visibility. The
potential also exists for isolated thunderstorms, especially over
windward waters. Fewer showers are expected by the weekend as the
trough weakens.

The persistent trade winds will generate rough and choppy surf along
E facing shores through the week. Gradually diminishing medium-
period swells out of the NW and N will continue to trend down today.
A small, medium-period NW swell is expected Wednesday, followed
by a larger, longer period NW swell Friday and Saturday that will
likely produce peak surf heights just below near High Surf Advisory
levels.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 6 AM HST Wednesday for Big Island
Summits.

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


&&

$$


DISCUSSION...JVC
AVIATION...TS/WALSH
MARINE...Birchard