Area Forecast Discussion Issued by NWS Honolulu, HI
000
FXHW60 PHFO 110139
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
339 PM HST Wed Apr 10 2024
.SYNOPSIS...
A low pressure system will bring the potential for increased
heavy showers and thunderstorms across Kauai and surrounding
waters midday Thursday through Friday. A period of unsettled and
showery weather will also reach Oahu during the day Thursday and
continue into Friday morning. The low pressure system will weaken
Saturday with the remnants sweeping across the middle of the state
by Sunday into Monday.
&&
.DISCUSSION...
A developing low far to the northwest of the state will influence
our weather, bringing unsettled conditions to western portions of
the state Thursday and Friday. This low pressure will weaken over
the weekend, with the remaining trough and unsettled weather
moving to the middle of the state by Sunday and Monday. There are
some uncertainties remaining and so the details are subject to
change and recommend closely monitoring the forecast as it evolves
over the next several days.
Kauai County will be the area of primary threat for heavy rainfall
later Thursday through Friday. An area of increased moisture,
instability and convergence moving into the state from the west
and southwest, will produce favorable conditions for the
development of heavy rainfall and thunderstorms. Cannot rule out
the possibility of strong to severe thunderstorms especially
later Thursday night and Friday morning.
Indications from most recent model guidance are that showery
conditions will likely reach Oahu and surrounding waters on
Thursday as the edge of the moisture convergence and instability
clips by the island during the day. Have raised chances of
rainfall for Oahu, and with with ESE flow, the potential for a
Koolau Mountains rainfall convergence band will need to be
monitored. The heaviest rainfall totals are still indicated by
models for the area around Kauai tomorrow through Friday, with
several inches of rain possible. The flash flood watch continues
in effect for Kauai County Thursday afternoon through Friday.
The moisture band pulls back to the west on later Friday and
Saturday, confining the threat of rainfall more to just Kauai
during that period. As the main low to our northwest begins to
lift away to the northeast, a trough will be dragged across the
middle of the state Sunday into Monday. The trough will be
weakening, although moisture and weak convergence will help
concentrate light to moderate rainfall along the band as it
drifts into Oahu and over Maui County later Sunday and Monday.
&&
.AVIATION...
To our NW a low pressure is rapidly developing and will lead to
decreasing, veering low-level wind flow over parts of the islands
through tonight. Moderate to locally strong E winds will persist
over the Big Island, while lighter SSE winds are expected over
the rest of the islands. VFR conditions should prevail through
tonight. SHRA and MVFR cigs/vsbys will mainly occur over windward
and mauka locations. Sea breezes with increasing cloud coverage
and some SHRA are possible over the lee sides today.
As for tomorrow, a convergence band looks to develop W of the
islands and approach Kauai County. Increased moisture moving over
the islands from the S will bring the increasing potential for
IFR/MVFR conds especially in any +SHRA/+TSRA.
&&
.MARINE...
Weakening high pressure to the distant northeast and rapidly
developing low pressure northwest of Kauai will lead to a
decreasing and veering low-level southeast wind flow over Kauai
and Oahu waters, while locally strong easterly winds are expected
over waters farther east for the next couple of days. The Small
Craft Advisory (SCA) that was previously issued for Alenuihaha
Channel, Pailolo Channel, and Maui windward waters has been
expanded to also include Big Island waters with this afternoon`s
forecast updates.
The low will remain nearly stationary northwest of the islands
for several days, then move slowly northeast this weekend. An
associated convergence band is expected to move over Kauai waters
on Thursday, then potentially linger for a few days before
drifting eastward through the weekend. As the band drifts east,
moderate winds will likely veer to the south and southwest over
Kauai and Oahu waters, with lighter winds veering to the southeast
over the Big Island.
A medium-period north-northwest swell will gradually diminish
Thursday. By the weekend, the low NW of the islands could aim a
significant medium-period northwest swell at the islands that
would arrive early next week. Surf along east facing shores will
remain somewhat elevated for the next couple of days with short-
period wind waves generated by an upstream fetch of fresh trade
winds. For south facing shores, a series of long-period small
south swells will support small surf throughout the next few days.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Thursday afternoon through Friday afternoon for
Niihau-Kauai-
Wind Advisory until 6 PM HST Thursday for Big Island Summits.
Small Craft Advisory until 6 PM HST Thursday for Maui County
Windward Waters-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters-Big Island Southeast Waters.
&&
$$
DISCUSSION...Brenchley
AVIATION...Walsh
MARINE...Vaughan