049
FXHW60 PHFO 121908
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
908 AM HST Sun May 12 2024

.SYNOPSIS...
A land and sea breeze pattern will favor clouds and showers over
island interiors for the next few afternoons. A kona low will then
bring a threat of heavy rain to the area from Wednesday night
into the weekend.

&&

.DISCUSSION...

Light easterlies will veer to southeasterly during the next couple
of days supporting a continued land and sea breeze pattern. This
will spell interior clouds and showers along sea breeze boundaries
followed by clearing and a transition to offshore showers each
night. This veered southeasterly flow is forecast to develop as a
consequence of a digging mid-latitude trough which is presently
centered along the International Dateline. This will advect higher
and more uncomfortable dewpoints in the upper 60s to near 70 into
the region by Monday night where they will likely stay for most or
all of the week.

Deep layer flow over the islands then veers to southwesterly as
aforementioned trough closes off and begets a kona low positioned
near 30N by Tuesday night. Large scale ascent will increase modestly
during this time as moisture transport into the area increases. The
gradient at the surface will remain light during this time perhaps
resulting showers that remain largely offshore courtesy of island
land breezes. South to southwest flow reaches the surface during
Wednesday, increasing confidence in a shower threat for all locales
thereafter. Stability around 500mb and above is relatively high to
start, but if the low remains established through the weekend, deep
convection and isolated thunderstorms will become an increasing
threat as stability erodes.

At this stage, global model consensus remains quite strong that
convergent SW flow will support a swath (or swaths) of moderate to
potentially heavy rainfall over the islands perhaps as early as
Wednesday night and continuing into the weekend. Key differences
arise in the guidance by the weekend when the resident kona low is
modeled to phase with additional energy digging southward out of the
northern branch of the jet stream. This will likely have significant
consequences for the location of the heavy rain band heading into
the weekend. The key message is that an elevated heavy rain and
potential flooding threat has emerged in the period from Wednesday
into the weekend.


&&

.AVIATION...

A lingering upper level disturbance will gradually weaken through
today but could still provide enough instability for a few heavy
showers across the state and isolated thunderstorms over the Big
Island. Winds will remain light enough to allow for sea breezes
this afternoon where clouds and showers could build up over island
interiors. Overall, showers should be slightly less
widespread/intense than yesterday, but MVFR and even IFR
conditions will still be possible in any of the heavier showers.

AIRMET Sierra for tempo mountain obscuration is in effect over the
east facing slopes of the Big Island and will likely remain in
place through much of the day. AIRMET IFR could be needed if
showers become heavy and persistent. AIRMET Sierra is also in
effect for Maui, Oahu and Kauai this morning due to tempo mountain
obscuration. This AIRMET may be needed on and off throughout today
and tonight for portions of the smaller islands due to shower
activity.

AIRMET Tango for moderate to isolated severe mid to upper level
turbulence remains in effect and will likely improve later this
morning as the area of stronger turbulence moves east.

AMD NOT SKED for PMDY continues due to equipment issues, with no
timeline for restoration.

&&

.MARINE...

Moderate to fresh east-southeast trade winds will build across
the island chain today and persist through Monday. Winds will
weaken Monday night and become more southerly on Tuesday as
troughing amplifies to the west of the state. Moderate southerly
winds will develop in advance of a front Wednesday. The front will
then move into the islands on Thursday, with moderate northwesterly
winds developing behind the front over the western end of the
state and moderate southerly winds prevailing ahead of the
feature.

Surf along south facing shores will slowly decline today through
Monday. Another series of overlapping, long-period south swells
will begin moving in early Tuesday, with these reinforcements
giving another noticeable boost to south shore surf through the
rest of the week.

A small, short-period north swell will decline today. A
reinforcing small, long-period northwest swell will build tonight,
giving north shore surf a boost Monday and Tuesday. A series of
small reinforcing northwest swells will keep some small surf
moving into north facing shores Wednesday into the weekend.

Surf along east facing shores will remain well below normal
levels through late this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...JVC
AVIATION...Farris
MARINE...Vaughan