832
FXHW60 PHFO 310723
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
923 PM HST Thu Jan 30 2025

.SYNOPSIS...
A solid area of rain over Oahu and Maui County this evening, with
embedded areas of heavy showers and thunderstorms, is leading the
main cold front passing across Kauai. This area of heavy
precipitation and storms will shift east from Oahu this evening
into Maui County through early Friday. A Severe Thunderstorm Watch
is in effect through 1 AM HST Friday from the Kaiwi Channel to
the Alenuihaha Channel including Maui County, as a few of these
thunderstorms could become severe and produce damaging winds.
There has and will be intense rainfall rates within this large
area of precipitation that are capable of producing flash
flooding. Strong to severe southwest winds are also possible as
this line and the trailing cold front passes across the island
chain from tonight through Friday. Conditions will gradually
improve as cooler and drier west air fills in behind the front
from Friday through the weekend. Cool and breezy trade wind
weather is expected through the first half of next week.

&&

.DISCUSSION...
The majority of the state and surrounding coastal waters remains
within the warm sector of a 987 mb storm force low positioned
about 500 miles north of Lihue, Kauai, at 8 AM HST this evening.
Strong, deep layer southwesterly winds persist this afternoon as
evidenced by local island radar VADs. Many afternoon into early
evening surface observations have confirmed sustained 40 mph
southwest winds with gusts over 50 mph on each island. Communities
just downstream of north and east-facing terrain experiencing
downslope accelerations, in addition to passing storm downdraft
winds, has produced nearly statewide strong winds. These strong
wind gusts have been responsible for many downed trees and power
lines leading to power outages. This wind threat will remain
unchanged for the eastern half of the state through tonight. The
ongoing High Wind Warning may need to be pared back from the west
as the front travels east toward Oahu into early Friday morning.
Veering weakening winds to the west northwest over the western
half of the state (Kauai and Oahu) will likely have the High Wind
Warning expiring by 6 AM HST Friday for Kauai and Oahu. The cold
front is passing through east Kauai (as of this writing). The
front is expected to fall apart over central state in response to
weakened forcing and the influx of a drier, post frontal dry air
mass. Little will remain of the front once it reaches Oahu during
Friday`s predawn hours.

The Severe Thunderstorm Watch will remain in effect until 1 AM
Friday morning to account for this moderately unstable and
strongly sheared air mass from the Kaiwi Channel eastward this
evening. Due to the progressive nature of the rain, the main
near term thunderstorm threat will be from localized wind gusts
up to and in excess of 60 mph. Today`s rain episodes of rain rates
of 1 to 4" per hour rates over the entire island of Oahu induced
the flooding of many roads and low-lying areas while producing
some minor flooding along various streams. Public road closures
are possible in those areas that experienced the highest rain
rates. Landslides are also possible within steep terrain. The
latest deterministic, global scale guidance indicates that the
greatest mid-level instability will continue shifting east into
Maui County through midnight, Big Island during the day Friday.
Higher resolution modeling propagates the highest QPF quickly
eastward onto Big Island by Friday sunrise, holding it up there
through the day. Thus, convection is still expected to migrate
eastward and will refocus heavy rain over more leeward areas of
Maui County for the remainder of the nocturnal hours.

High resolution model guidance is depicting that the heaviest rain
activity will shift east of Maui and into Big Island early Friday
morning, but the larger scale models paint the picture of the
greatest mid layer moisture/tightest instability gradient not
moving, or remaining anchored over Maui through most of Friday.
These inconsistencies hold onto higher chances of a slowing line
later tonight that could create a prolonged flooding threat for
the island of Maui well into Friday. This outcome would delay the
onset of heavy rain over Big Island and the snow over the summits
until late Friday morning and afternoon. The instability gradient
shifts over the Big Island late Friday into Friday night as low
pressure pulls away and overall forcing diminishes their flash
flood threat. The forecast over the eastern end of the state will
be highly dependent of overnight convective trends over Maui
County.

Pleasant, dry post-frontal air filters in over Kauai and Oahu
going into the weekend as trade winds return.

&&

.AVIATION...
Widespread heavy showers and strong to severe thunderstorms
associated with a cold front will continue to impact the eastern
half of the state into Friday. Expect localized strong
turbulence, minimal visibility, and low ceilings during this
period. While the threat of heavy showers and thunderstorms will
diminish over the western portion of the state as the front moves
through, periods of MVFR ceilings and visibility in light to
moderate showers, along with gusty westerly winds, will persist
overnight before gradually improving from west to east throughout
the day Friday.

AIRMET Sierra is in effect for IFR conditions over Maui County
and will need to be expanded to include the Big Island later
tonight. Additionally, AIRMET Sierra remains in effect for
temporary mountain obscurations above 2,000 feet across the
western end of the state.

AIRMET Tango is posted for temporary moderate turbulence below
10,000 feet and from FL270 to FL400 across the entire state.
Strong sustained winds and downsloping gusts are expected along
the north and east sides of the islands, warranting an AIRMET for
sustained winds of 30 knots or greater. Light icing is anticipated
between 14,000 feet and FL240. These hazards will likely persist
through Friday morning.


&&

.MARINE...
Strong low pressure passing N of the islands will continue to
bring widespread impactful weather in the form of strong to
severe thunderstorms, wind gusts in excess of 50 kt, and zero
visibility in areas of blinding rain. Main impacts overnight will
shift E of Kauai and Oahu. The Gale Warning has been dropped for
waters W of Kauai, and expanded to waters around Maui County and
the Big Island, while a Small Craft Advisory remains posted
elsewhere.

Moderate to fresh W to NW winds with improving weather trends
will quickly build in after the front passes through each island.
The front should be pushing through the western half of the state
overnight and the eastern half of the state Friday night into
Saturday. Moderate to locally strong NE trade winds will develop
by Sunday as high pressure builds far NW of the islands.

A long-period N swell will rapidly build tonight, then gradually
diminish Friday, and a High Surf Advisory is posted for N facing
shores of nearly all islands. Additionally, the powerful low
passing N of the islands will produce a wide range of swell periods
with directions ranging anywhere from the SW to NNE, with the
largest pulse being a NW swell that will build on Friday.

The locally generated wind waves that are making for sloppy surf
along S and W facing shores will linger through Friday. Another N
swell will arrive Sunday and peak Monday, producing high surf
along N facing shores. A couple moderate sized WNW swells are
also expected, with a smaller one this weekend, and a slightly
larger one from Monday into Wednesday, with a peak on Tuesday.


&&

.FIRE WEATHER...
Critical fire conditions are not expected during the forecast
period.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday afternoon for Niihau-Kauai Leeward-
Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central
Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-
Maui Leeward West-Haleakala Summit-Kona-Kohala-Big Island
Interior-Kauai North-Kauai East-Kauai South-East Honolulu-
Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai-
Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley
North-Maui Central Valley South-Windward Haleakala-Kipahulu-
South Maui/Upcountry-South Haleakala-Big Island South-Big Island
Southeast-Big Island East-Big Island North.

High Wind Warning until noon HST Friday for Niihau-Kauai Leeward-
Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central
Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-
Maui Leeward West-Kona-Kohala-Big Island Interior-Kauai North-
Kauai East-Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-
Koolau Windward-Koolau Leeward-Molokai-Lanai Windward-Lanai
Leeward-Lanai South-Maui Central Valley North-Maui Central
Valley South-Windward Haleakala-Kipahulu-South Maui/Upcountry-
South Haleakala-Big Island South-Big Island Southeast-Big Island
East-Big Island North.

High Surf Advisory until 6 PM HST Friday for Niihau-Oahu North
Shore-Olomana-Maui Windward West-Kauai North-Kauai East-Koolau
Windward-Molokai Windward-Molokai North-Maui Central Valley
North-Windward Haleakala-Big Island East-Big Island North.

High Wind Warning until 6 PM HST Friday for Haleakala Summit.

High Wind Warning until 6 AM HST Saturday for Big Island Summits.

Winter Storm Warning until 6 AM HST Saturday for Big Island
Summits.

Small Craft Advisory until 6 AM HST Friday for Kauai Northwest
Waters-Kauai Leeward Waters-Oahu Windward Waters-Oahu Leeward
Waters-Kaiwi Channel-Big Island Windward Waters-Big Island
Southeast Waters.

Gale Warning until 6 AM HST Friday for Kauai Windward Waters-
Kauai Channel-Maui County Windward Waters-Maui County Leeward
Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters.


&&

$$


DISCUSSION...Blood
AVIATION...Gibbs
MARINE...Birchard
FIRE WEATHER...Clark