Area Forecast Discussion Issued by NWS Honolulu, HI
000
FXHW60 PHFO 140200
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Wed Mar 13 2024
.SYNOPSIS...
A weak cold front will continue to make its way down the island
chain before dissipating near the Big Island late tonight. An
associated band of moisture will increase showers tonight,
particularly across the central islands. A secondary boundary will
move southward as well, increasing surface wind speeds into the
moderate to locally breezy range as they become northeasterly.
Some moisture may linger near the eastern end of the state
through Friday, but otherwise, cooler and drier weather is
expected Friday through the weekend.
&&
.DISCUSSION...
Advanced scatterometer (ASCAT) data and afternoon surface
analysis reveal two distinct boundaries in the area. The first is
a weak cold front located near Oahu, where showers just ahead of
this feature produced rainfall between 1 and 2 inches for portions
of west and central Oahu earlier today. More recently, showers
have waned, but a few scattered light to moderate showers remain
in the vicinity of Oahu as this boundary moves southeastward
towards Maui County. Meanwhile, a secondary boundary lies
northwest of Kauai, where a distinct increase in winds are noted
in the ASCAT and model data. Elsewhere, afternoon sea breezes
within a weak background flow regime have resulted in an increase
in interior and leeward showers across Maui and the Big Island,
but these should diminish overnight.
The initial boundary will continue moving southeast and diminish
near the Big Island tonight. Meanwhile, moderate to locally
breezy northerly flow will fill in across the islands from west to
east tonight through Thursday morning as the secondary boundary
approaches. Hi-res guidance suggests that low-level convergence
will increase as surface winds increase, leading to enhanced
rainfall across the central islands tonight (particularly across
windward locations) before spreading to the Big Island early
Thursday.
Moisture may linger across the central and eastern islands
Thursday into Friday, producing occasional showers that will
generally favor windward and mauka locations. A drier and
slightly cooler post- frontal airmass will settle in behind the
front near the western end of the state.
Mid and upper level ridging will build north of the islands
Thursday and Friday, increasing stability as a weak surface high
builds north of the state. Northeast winds will become more
moderate Friday through the weekend as they shift more easterly.
Expect a return to a drier trade wind pattern this weekend, with a
series of progressive low pressure systems and fronts moving
eastward well north of the main Hawaiian Islands into next week.
&&
.AVIATION...
A weak cold front will continue to make its way down the island
chain before dissipating near the Big Island late tonight. This
feature, along with a jet streak moving over the state today and a
second boundary pushing south overnight into tomorrow, will help
to enhance shower development and produce periods of MVFR or lower
conditions over portions of the Hawaiian Islands through the
forecast period. Otherwise, VFR conditions will prevail.
Winds will continue to be light to moderate ahead of the front,
with an uptick in northerly wind speeds behind a second boundary
moving through tonight into tomorrow. In the lighter flow across
the eastern end of the state, sea breezes will continue to
contribute to cloud and shower development over mountain and
interior sections late this afternoon and land breezes may help
to clear things out overnight. Then showers assoicated with the
front will push south through the rest of the state overnight into
Thursday morning.
AIRMET Sierra is in effect across Oahu for tempo mountain
obscuration due to low clouds and showers. This AIRMET will likely
need to be shifted or expanded across portions of the island
chain through tomorrow morning as the front progresses.
AIRMET TANGO is in effect across Hawaii for tempo moderate
turbulence between FL250 and FL360 due to the jet streak moving
through the region. This AIRMET will likely be needed through the
evening.
&&
.MARINE...
A weak front is moving eastward across the main Hawaiian Islands.
The front is expected to dissipate near Maui and the Big Island
tonight. Moderate to fresh northerly winds will fill in behind the
front through Thursday. The winds will weaken and gradually shift
Thursday night to become northeasterlies on Friday. Over the
weekend, the winds will drop into the light to moderate range and
will be coming out of a more typical east-northeasterly trade wind
direction. Winds are expected to remain mostly below Small Craft
Advisory (SCA) thresholds through early next week. SCA level seas
will likely impact portions of the marine area as a large
northwest swell moves through Thursday into early Saturday.
Long period forerunners of a large northwest swell have reached
Buoy 51101 northwest of Kauai. This swell should reach the local
waters tonight and quickly build on Thursday. Warning level surf
is expected Thursday afternoon through Friday along the north and
west facing shores of the smaller islands. Surf may reach advisory
levels along the west facing shores of the Big Island Thursday
night through Friday night. This swell will decline Friday night
and Saturday. A reinforcing northwest swell should arrive Saturday
night, keeping some moderate sized surf in place along north and
west facing shores through early next week.
South facing shores should have small surf through Saturday. A
south swell arriving Sunday should produce a slight increase in
the surf that is expected to persist through Monday. East shore
surf will trend down during the next couple days, then remain well
below normal through early next week.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning from 6 AM Thursday to 6 PM HST Friday for
north and west facing shores of Niihau, Kauai, Oahu, and Molokai,
and for north facing shores of Maui.
&&
$$
DISCUSSION...Vaughan
AVIATION...Farris
MARINE...Kodama