NWS Honolulu, HI wrote its last area forecast discussion before the first event at Jan 27, 10:02 AM HST, 1 hour 58 minutes earlier.
Area forecast discussion, Jan 27, 10:02 AM HST, 1 hour 58 minutes before
Area Forecast Discussion
National Weather Service Honolulu HI
1002 AM HST Fri Jan 27 2023
.SYNOPSIS...
Cool, dry and breezy northeast trade winds will continue over
Kauai and Oahu through early Saturday, as cloudy and locally wet
conditions persist near a dissipating front over the Big Island and
Maui County. A developing trough will linger over the island chain
through Monday, acting as a focus for cloud and shower development
statewide, while also bringing strong northeast trade winds to Kauai
and Oahu. A developing low aloft will bring the potential for
locally heavy rainfall from Saturday into Monday, especially over
windward areas.
&&
.DISCUSSION...
A stalled surface front has transitioned to a trough, and is acting
to focus showers and isolated thunderstorms over the area from Maui
to N Big Island, while stable, cool and mostly dry conditions
persist over Oahu and Kauai. A sharp upper-level trough is
generating layered clouds across the Big Island and parts of Maui
County, while maintaining enough instability to trigger a few
thunderstorms. The heaviest showers this morning have been over
windward East Maui, in the Alenuihaha Channel, and over near shore
windward Big Island waters, with a strong thunderstorm recently
passing near Upolu Point. A rain gage at West Waialuaiki has
recorded nearly 10 inches of rain over the past 24 hours. In
contrast, the breezy NE flow over Oahu and Kauai is delivering
broken to overcast stable low clouds that are stacking up along
windward slopes. Although it is mostly dry, some of these clouds
have managed to drop a few hundredths of an inch of rain while dew
points in the mid- to upper-50s are maintaining a cool feel.
Expect some small changes through tonight as the surface trough
drifts W, and the upper level trough broadens and slowly weakens.
The focus for rainfall should remain along the surface trough,
maintaining higher rain chances and the possibility of thunderstorms
along windward slopes of northern Big Island and Maui County.
Interior sections of the Big Island may experience an afternoon
heavy shower or thunderstorm, as high clouds have thinned somewhat
this morning. In addition, the Big Island Summits could see snow
showers, mainly in the afternoon. On Oahu and Kauai, expect morning
windward clouds to deliver a few light sprinkles, then largely burn
off by mid morning. Dew points may creep up as the air modifies
tonight, but chances for showers will remain very low.
For Saturday, the surface trough will drift W as an upper level
trough sharpens W of the islands. Wet conditions will hold across
windward Maui County, but guidance has been consistent in spreading
rainfall to Oahu Saturday, with showers primarily affecting windward
areas. The deepening upper level trough will generate more
widespread high clouds and may trigger a few thunderstorms across
the wetter windward areas. Interior Big Island could also see a few
afternoon thunderstorms and summit snow showers as well. On Kauai,
drier conditions will persist.
Saturday night into Monday, chances for heavy rainfall and
thunderstorms increase, but the specifics remain uncertain. The GFS
and ECMWF model both sharpen the upper level trough just west of
Kauai Saturday night and produce a compact upper level low to the
southwest of the state Sunday. This will lead to mid level ascent
that will thicken high clouds over the island chain and produce
moist and unstable conditions. The GFS continues to produce what
appears to be a spurious surface low over the state, and the more
believable ECMWF solution draws ample moisture over the Big Island,
while the lingering surface trough continues to feed low level
moisture over windward slopes of Maui County and Oahu, and perhaps
to Kauai be late Sunday. There is increased confidence that the
sharpening low level trough will lead to strengthening NE trade
winds over Kauai and Oahu, potentially strong enough to warrant a
Wind Advisory on Sunday.
Though wet conditions will likely linger into Monday, the GFS and
ECMWF show the upper level low drifting away from the state to
the southwest, suggesting that chances for heavy rainfall will
decrease as high clouds thin. Breezy NE to E winds will persist,
focusing the bulk of the shower activity over windward areas.
Beyond Monday, the forecast favors trade winds, but the uncertainty
remains unusually high. The longwave pattern points toward lingering
upper level troughing, suggesting that we could stay in a wetter
regime.
&&
.AVIATION...
A surface trough is stalled over the Alenuihaha Channel. The morning
sounding at Hilo reveals deep moisture and moderate instability
throughout the air column ahead of the front. The sounding at Lihue
revealed dry and stable conditions in its wake.
Persistent rain showers and localized thunderstorms are thus
expected across the eastern half of the state throughout the day
today and into the evening hours. Locally heavy showers or
thunderstorms could linger across East Maui and the Big Island
through the overnight hours. Elsewhere across the state, extensive
areas of low topped clouds with limited shower activity will
prevail.
Occasional MVFR conditions in low clouds and showers are likely
statewide today, especially along north and east facing slopes and
coasts. Brief IFR in heavy showers or thunderstorms is possible over
Maui and Windward Big Island. AIRMET Sierra for mountain obscuration
remains in effect for Windward portions of Oahu, Molokai, Maui, and
the Big Island. Conditions are expected to improve over Oahu this
evening, but are expected to continue through Saturday morning for
the remaining islands.
&&
.MARINE...
A trough over the eastern part of the state will continue to produce
showers and isolated thunderstorms around Maui County and the Big
Island through tonight, then shift westward slightly on Saturday to
include Oahu waters as well. Moderate to locally strong northeast
winds will strengthen today as a high builds northwest of the state.
Winds will increase to near gale speeds over the western half of the
state this weekend as the high strengthens and a developing trough
over the state helps sharpen the gradient. A Small Craft Advisory
(SCA) is currently in effect due to a combination of high seas and
locally strong winds for most waters through this afternoon. The SCA
zones will need to be readjusted this afternoon as seas drop below
10 feet throughout the day.
The current (310-320 degrees) northwest swell is fading, but still
producing surf at low-end High Surf Advisory (HSA) levels this
morning. The HSA is expected to be dropped by this afternoon as the
swell drops further. A series of moderate north swells will move
through the local waters later today into the first half of next
week. These swells will keep surf elevated along north facing
shores. A long-period, moderate northwest swell (310 degrees) is
expected to boost surf heights back to advisory levels along north
and west facing shores Sunday into Monday. Surf along east facing
shores should see some wrap from the north to northwest swells
through early next week. South shore surf will remain small into
early next week.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for north facing
shores of Niihau, Kauai, Oahu, Molokai, and Maui.
Flood Watch through Sunday afternoon for Maui Molokai Lanai and
Kahoolawe.
Small Craft Advisory until 6 PM HST this evening 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-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters.
&&
DISCUSSION...Birchard/Wroe
AVIATION...Bedal
MARINE...TS