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000
FXHW60 PHFO 111359
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
359 AM HST Thu Apr 11 2024

.SYNOPSIS...

A strong low pressure system northwest of the state will develop a
broad rainband just west of Kauai County and surrounding waters.
The proximity of this rainband will continue the threat of
potential heavy showers and thunderstorms for Kauai County and
possibly spread as far as Oahu through Friday. The rainband may
shift west briefly Saturday before sweeping across the state from
west to east Sunday through Monday.

&&

.DISCUSSION...

A 1000 mb storm low roughly 550 miles northwest of Kauai and a
weak high pressure to far northeast continues to generate gentle
southeast winds over Kauai and Oahu and more gentle to locally
breezy east to southeast winds elsewhere. Satellite imagery shows
high clouds are now streaming over most the island chain with
some lower clouds streaming from the east and southeast along Big
island and Maui. Radar shows scattered light to moderate showers
have been steadily moving in along Big Island southeast and
windward coasts overnight and along exposed southeast areas of
Maui. CIMSS satellite precipitable water imagery shows a tongue
enhanced moisture building over the state with precipitable water
values ranging between 1 to 2 inches.

As the low continues to rapidly intensify today, hi res models
continue to show strengthening breezy east to southeast winds and
a broadening of the associated rainband. The Flood Watch for
Kauai County will start at noon today and persist through Friday
due to the proximity of this rainband and upper level dynamics
that will likely produce several inches of rainfall along with the
chance for isolated thunderstorms. If this rainband or low moves
further east than model guidance, then there is a chance Oahu may
also receive a few heavy showers. Elsewhere, chances of showers
will increase for sheltered leeward and interior areas where
seabreezes can develop this afternoon. Chance of showers will
continue for exposed east and southeast areas of Maui and the Big
Island as winds remain more east to southeasterly.

The rainband is expected to shift west Friday afternoon and
Saturday as the low shifts north and weakens slightly. This may
confine the threat of rainfall more to just Kauai during that
period. The low is then expected to continue to slowly weaken
while tracking northeast late Saturday through early next week.
During this time winds will become more southerly over the western
end of the state ahead of the associated band of moisture through
Saturday night. West to northwesterly winds may fill in Sunday
into early next week from west to east which may push the
associated moisture band across the the state. Upper level
dynamics may also be conducive for active showers within this
band, especially as the converging winds interact with island
topography.

&&

.AVIATION...
In the short term, 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. Moderate to fresh E trade winds will continue over the Big
Island, delivering periods of MVFR VIS/CIG in SHRA, and AIRMET
Sierra is posted. VFR conditions will generally prevail elsewhere
as limited showers are currently embedded within the low-level
flow. Otherwise, latest observations and satellite images show
increasing layered mid- and upper-level clouds moving over the
islands from the SW, with the potential for light icing.

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


&&

.MARINE...
Moderate to strong east-southeast winds will steadily increase
into the fresh to strong category for all waters today as a
storm-force low evolves several hundred nautical miles northwest
of the state. The east-southeast winds will peak later today, hold
into Friday, then ease into the moderate to fresh category by
Saturday as the system begins to lift northeastward. As this
system passes the state far to the north Sunday into early next
week, the winds will steadily veer out of the south to southwest
and potentially return to the fresh category over the western end
of the state by Sunday. Moderate to fresh northerly winds are
possible Monday, with a return of a more typical trade wind
pattern by midweek as high pressure builds to the north.

Surf along exposed north and west facing shores will steadily
ease today as a medium-period north-northwest swell moves out.
Expect small surf to persist through Saturday. An upward trend is
possible later Sunday as a small long-period north-northwest
swell arrives from a system across the far northwest Pacific.
This upward trend will continue through the first half of next
week as the aforementioned low nearby to the northwest lifts
northeastward over the weekend. Heights could reach advisory
levels Monday night through Tuesday night as this swell peaks.
Thereafter, expect a gradual downward trend with the swell
direction shifting out of the north-northwest by Thursday.

Surf along east facing shores will become rough as the winds peak
today and tonight, but should steadily trend down over the
weekend as the winds veer out of the south. Small surf will
persist next week.

Surf along south facing shores remain small with mainly background
south-southwest swell expected. The next long-period pulse is
expected late Friday that should hold through the weekend before
moving out. If the moderate to fresh south-southwest winds
materialize as advertised later in the weekend, conditions may
become rough and choppy along southerly exposures.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from noon HST today through Friday afternoon for
Niihau-Kauai-

Wind Advisory until 6 PM HST this evening for Big Island Summits.

Small Craft Advisory until 6 AM HST Friday for Oahu Windward
Waters-Kaiwi Channel-Maui County Windward Waters-Maui County
Leeward Waters-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.


&&

$$


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