High Surf Warning 6, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
1015 AM HST Tue Feb 28 2023

.SYNOPSIS...
Wet and windy trade wind weather will persist over the next
several days. An upper level disturbance just northeast of the Big
Island will enhance showers and could bring some isolated
thunderstorms to the eastern half of the state. The highest
rainfall amounts are are expected over East Maui and the windward
slopes of the Big Island throughout this week. Trade winds should
gradually lower Friday into the weekend as a cold front
approaches the region from the northwest. A cold front will likely
bring an increase of heavy showers especially leeward areas during
the first half of next week.

&&

.DISCUSSION...
Strong high pressure north of the state will continue to maintain
windy trade wind conditions across the state. Aloft, water vapor
imagery is showing an upper level low just northeast of the Big
Island and is enhancing our trade wind showers. This upper low is
expected to gradually move closer to the state over the next
several days and will continue to produce a wet trade wind pattern
across the state.

Morning sounding from Hilo shows steep low-level lapse rates with
a weak inversion. With the unstable atmosphere in place, lightning
will be possible with any showers over windward Big Island and
possibly east Maui. Overall the weather forecast does not change
much during the next several days with wet and windy conditions
continuing. Trade winds are actually expected to slightly
strengthen even more tonight into Wednesday, thus the Wind
Advisory was updated this morning to include the entire island of
Oahu and Kauai. As for rainfall, showery weather will continue
over the western half of the state while thunder trades will
remain possible over the eastern half of the state, primarily
windward areas. Some minor flooding will be possible at times due
to the heavy downpours. The greatest rainfall is expected over the
mid-slopes of windward Big Island where frequent heavy showers
are expected. Due to periodic breaks between each heavy showers,
significant flooding is not expected at this time. The main
concern and uncertainty during the next few days would be if we
see any shower training over a particular area due to the unstable
atmosphere.

Trade winds are expected to gradually weaken Thursday through the
weekend and could become light and variable by Sunday as a front
begins to approach the state from the northwest. Forecast models
are also showing a trough developing east of the state this
weekend. The general trend would be for a decrease of shower
activity this weekend.

&&

.AVIATION...
High pressure north of the islands will keep strong and gusty
trade winds in place during the next couple days. An upper level
low northeast of the Big Island moving southwest towards the state
will provide some instability to the atmosphere. A few heavy
showers and isolated thunderstorms will be possible for the Big
Island summits and windward areas of Maui this afternoon. Within
these heavier showers and thunderstorms, embedded IFR conditions
can be expected. Otherwise Clouds and showers will favor windward
and mauka areas, but a few will reach leeward communities at
times. Some MVFR cigs/vsbys can be expected in the passing
showers, with showers most prevalent over windward slopes and
coasts.

AIRMET Sierra remains in effect for mountain obscuration over
windward sections of most islands. This AIRMET will likely remain
in place through the morning hours, with some improvement
possible over windward sections of Kauai and Oahu this afternoon.

AIRMET Tango remains in effect for moderate to isolated severe low
level turbulence over and downwind of the terrain of all islands.
AIRMET Tango is also in effect for strong surface winds across the
entire state.

&&

.MARINE...
Rough conditions will continue across the local waters into the
second half of the week as strong high pressure remains to the
north. Overnight satellite data showed 25-35 kt winds with seas
hovering in the 10-15 ft range, which line up well with nearshore
buoy observations this morning. Guidance supports this and depicts
a large belt of strong northeast to east trades over and upstream
of the state through much of this week, with gales continuing
through midweek over the windier waters and channels of Maui County
and the Big Island. A pattern transition is likely this weekend
as a cold front approaches, leading to a break in the strong winds
and rough seas.

Surf along east facing shores will build today, with heights
nearing the warning threshold of 15 ft tonight through Wednesday
due to the aforementioned winds over and upstream of the state. A
downward trend is expected Friday through the upcoming weekend as
the ridge weakens and winds ease.

Surf along north facing shores will remain well below the seasonal
average through next weekend. Satellite data showed a large swath
of gales aimed at the area down the 310 degree directional band
associated with a system tracking eastward toward the Date Line.
This supports a small west-northwest swell arriving Friday, then
lingering into the weekend.

Surf along south facing shores will remain near the seasonal average
each day, with mainly wind swell wrapping into exposed areas.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Wednesday for Kauai Leeward-Kauai
Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-
Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-Maui
Leeward West-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 North.

High Surf Advisory until 6 PM HST Thursday for Olomana-Maui
Windward West-Kauai East-Kauai South-East Honolulu-Koolau
Windward-Molokai Windward-Molokai Southeast-Windward Haleakala-
Kipahulu-South Haleakala-Big Island Southeast-Big Island East-
Big Island North.

Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters.

Gale Warning until 6 PM HST Thursday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

DISCUSSION...Kino
AVIATION...Tsamous
MARINE...TS