National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXHW60 PHFO 110704
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
904 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 moisture band sweeping across the middle of the
state by Sunday into Monday.

&&

.DISCUSSION...

The afternoon surface analysis shows a ridge of high pressure
draped over the state from a weak high pressure to the far
northeast. A storm low has developed roughly 550 miles northwest
of Kauai. This setup has veered light winds out of the southeast
for the western half of the state with more light to breezy east
to southeast winds over the eastern half of the state this
afternoon. Satellite imagery shows high clouds streaming in from
west to east across Big Island with a mix of low to mid clouds
streaming up from the south and moving over Kauai. The rest of the
state shows a few clouds along interior and mauka regions this
afternoon with a few bands of stratus clouds filling in from the
south. Radar shows scattered light to moderate showers moving in
along windward and mauka regions of the Big Island and limited
showers elsewhere. Given the lighter winds over the small islands,
can expect a land breeze to develop tonight into early morning
Thursday, clearing clouds over leeward and interior areas while a
few clouds and showers may still build up along some exposed
windward areas, especially around the Big Island.

The main focus of the remaining forecast moving forward will be
associated with the moisture band produce by the storm low far
northwest of the state. This low is expected to rapidly intensity
in the next 24 hours that will strengthen the southeast winds
locally. In addition this low will drawn up significant moisture
from the south increasing dewpoints in the upper 60s to low 70s.
There is a Flood Watch out for Niihau and Kauai starting at noon
Thursday through Friday due to the proximity to the moisture
convergence band and upper level dynamics that will may produce
several inches of rainfall for this area along the the chance for
isolated thunderstorms. Latest Hi res models show that activity
may start around noon and persist into Friday. There is also a
chance a few heavy showers and thunderstorms may impact Oahu
during this time.

The moisture band pulls back to the west on later Friday and
Saturday and the low shifts north, confining the threat of
rainfall more to just Kauai during that period. As the main low to
our northwest begins to track to the northeast, the band of
moisture will drag across the middle of the state Sunday into
Monday. Upper level dynamics may also be conducive for active
showers within this band, especially as southwesterly winds
interact with island topography.


&&

.AVIATION...
The gradient between high pressure to the distant NE and deep-
layer low pressure to the NW will support a low-level flow that is
veered to the SE over the Kauai end of the island chain through
Thursday. Moderate to fresh E trade winds are expected to
continue over the Big Island. Periods of MVFR VIS/CIG in SHRA will
affect windward Big Island, with VFR conditions generally
prevailing elsewhere as limited showers are currently embedded
within the low-level flow. Otherwise, latest satellite images show
increasing mid-level (between 8 and 10 kft) clouds over part of
the state.

Increased moisture moving over the area from the S will likely
impact Kauai and surrounding waters (and potentially Oahu) on
Thursday, bringing the potential for heavy showers and
thunderstorms that would result in localized IFR conditions and
widespread MVFR. Otherwise and elsewhere, limited windward
showers in the morning, with some afternoon clouds and a few
showers over leeward and interior areas.


&&

.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...Almanza
AVIATION...Birchard
MARINE...Gibbs