234
FXHW60 PHFO 191402
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
402 AM HST Sun Jan 19 2025

.SYNOPSIS...
Post-frontal dry and stable conditions dominate the Hawaiian
Island weather regime through the day. Recent northerly winds have
transitioned to traditional trade wind flow. Gentle to locally
breezy trades will persist through Tuesday afternoon. Shower
activity will favor windward and mauka areas Monday and Tuesday.
A major mid week pattern change may develop in response to an
evolving northern upper trough digging south toward the islands.
This will increase precipitation chances although there is a fair
amount of uncertainty regarding this trough`s potential impact
upon regional winds and rainfall distribution.


&&

.DISCUSSION...
Today will be another beautiful day in paradise as the region
remains under a dry air mass and gentle trade winds. Surface
observations have many communities waking up to mainly clear to
partly cloudy skies in the middle 60s to lower 70s, with middle
50 to lower 60 dew points, under gentle trades. With the exception
of higher vog concentrations south of Halema`uma`u crater over
Big Island`s Ka`u region, skies will remain mainly clear with the
occasional band of windward stratocumulus streaming by to the
south. Recent UH vog modeling keeps SO2 emissions focused over the
south and east-facing slopes of Big Island through tomorrow, with
lighter concentrations wrapping around into leeward Kona regions.
Due to strengthened trades providing better mixing throughout the
near 5k ft boundary layer depth, volcanic emissions are not
expected to reach the smaller islands. Other than a sprinkle here
or there within higher elevations, statewide weather will remain
dry through this afternoon. Today`s weather will be very similar
to yesterday`s with a cool morning leading to a comfortably warm
day in upper 70s to lower 80s at or near the coast, lower to
middle 60s above a few thousand feet elevation. Surface high
pressure establishing itself north northeast of the island chain
will create a tight enough gradient back toward the islands to
produce a few days of gentle to breezy trades. A subtle increase
in lower to middle layer moisture advancing in from the north will
introduce more areal showers to the typically wetter windward
areas and mauka slopes. Mid to upper level ridging nosing in from
the west will maintain enough background stability, in tandem with
slightly lower than seasonable precipitable waters, to limit any
widespread significant rainfall through Tuesday.

The general model consensus going into the middle of the week
depicts falling heights downstream of a deepening Central Pacific
upper trough diving south toward the state. Uncertainty in this
mid to late week unstable wet and windier scenario remains
moderate regarding the development and timing of this positive-
becoming-negatively tilted trough`s mid to late week potential
impact upon the islands. There is a possibility that a closed off
low will develop in the base of the trough as it reaches our far
northern offshore waters late Wednesday into Thursday. While
there is less inconsistency between the GFS and EC solutions, the
signal is there for a weather regime change Wednesday through
Friday. While the 19/00Z deterministic EC solution rotates a small
surface low near Kauai on Friday. About a third of the EC
Ensemble members develop a near 1000 mb cut off low well north of
the chain (even less members in the GFS ENS). Not one member from
either ensemble drops it over the state. Thus, the more likely
scenario will be of a cold front passing through the area Thursday;
strengthening post-frontal northwesterly winds over the western
half of the state with moderate southwesterlies leading the
boundary over the eastern half of the state. A myriad of concerns
would include the monitoring of locally higher rain accumulations
and the subsequent flooding potential, strong gusty winds along
with the vicinity thunderstorms that will all be dependent upon
the movement (or retrogradation) of a cut-off low meandering north
of the state.


&&

.AVIATION...
VFR conditions will prevail, with moderate northeast trades
and scattered low clouds over windward areas. No AIRMETs are
expected.


&&

.MARINE...
A high pressure system passing just north of the Hawaiian Islands
will keep gentle to fresh trade winds in the forecast into Monday.
A shallow  cold front approaching and then moving into the
islands on Tuesday and Wednesday will produce more variable winds
along and east of the frontal band. Northwesterly winds will build
in behind the front as it passes through each island. A wet
weather pattern remains in the forecast with chances for some
thunderstorm activity along the front.

The current long period northwest swell will slowly decline
today. Surf heights along north and west facing shores will
steadily decrease in line with this decreasing swell energy. The
High Surf Advisory along exposed north and west facing shores
remains in effect and will likely be cancelled later this
afternoon as surf heights are expected to fall below our advisory
thresholds. The next northwest swell may produce advisory level
surf along exposed north and west facing shores from Tuesday into
Wednesday, then slowly fade through the end of the week.

East facing shore surf will remain choppy the next few days as
the trades build, and background south swell will keep surf small
on south facing shores through the coming week.

The Small Craft Advisory (SCA) remains in effect for waters
windier waters around Maui and the Big Island.


&&

.FIRE WEATHER...
Drier air will continue to move across the state, keeping minimum
afternoon relative humidity values at near critical thresholds.
However, winds look to remain just weak enough to preclude
critical fire weather conditions. While daytime more leeward wind
protected humidities may dip into the upper forties at times the
next few days, winds should remain on the low side of 20 mph.
Thus, the likelihood for critical fire weather conditions remains
relatively low through Tuesday.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai
North-Molokai Windward-Molokai North-Molokai West-Maui Central
Valley North-Windward Haleakala.

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Southeast Waters.


&&

$$


DISCUSSION...Blood
AVIATION...Gibbs
MARINE...Bohlin
FIRE WEATHER...Blood