NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
949
FXHW60 PHFO 100744 CCA
AFDHFO
Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
944 PM HST Mon Sep 9 2024
.SYNOPSIS...
Large scale light breezes have allowed daytime sea breezes and
nocturnal land breezes to dominate the island's near term wind
regime. These localized onshore breezes will introduce more
interior afternoon cloud build up with isolated showers to be
followed by overnight clear skies. A stalled weak boundary draped
across the northwest waters will assist in producing more showers
around Kauai before dissipating later Tuesday into Wednesday.
Trade winds will return Thursday and strengthen through the
weekend.
&&
.DISCUSSION...
A near stationary 1005 mb surface low approximately 750 miles
northeast of Oahu will be slowly retrograding southwest...its
stalled appendant trough over the north offshore waters about 100
miles north northeast of Kauai. This has created a col in the
regional pressure field thus suppressing the pressure gradient
back to islands from a large area of surface high pressure located
over 1,300 miles northwest of the state. Today's 00Z soundings
still depict a strong near 6k ft inversion with slightly higher
total precipitable waters focused along the west end where
moisture is pooling along the weak boundary north of Kauai. IR
satellite shows the most dense warm cloud cover hanging along this
boundary. Only weak radar returns from light shower activity
around the Garden Isle and Niihau moving south of the tail end of
the trough. As in previous nights within this very light synoptic
scale flow, expect starry skies as mauka drainage winds scour out
the majority of lingering late day clouds. The exceptions may be
along high elevation ridge lines and leeward Big Island zones
where low level moisture tends to get trapped below the inversion.
Higher moisture pooling along this weak meandering trough will not
only be the impetus to statewide light and variable winds but to
higher west state rain chances the next day or so. A diurnal
inland-pushing sea breeze boundary will initiate more Big Island
Kona region showers during the warmth of the afternoon. While the
vertical profile remains relatively dry in the middle and upper
levels over the eastern half of the state just downstream of this
boundary, the near surface boundary layer will remain moist enough
to keep days still feeling a touch more humid than normal as
lower elevations warm into the middle 80s.
The well-stacked upper level low in association with the
aforementioned surface low will begin to fill in and weaken into
an open wave trough as it slowly drifts off to the northwest
through Wednesday. The lack of any upper support will have the
surface trough washing out by Thursday. This will allow the
return of breezy trades from Thursday afternoon into the weekend.
A strong mid-level ridge will continue to support a stable, dry
and warm Central Pacific atmosphere through Thursday. As the upper
low sinks south and weakens upper ridging over the state later
this week, regional heights will subtly fall as mid levels
slightly cool. Higher east mid level moisture advecting into the
area during this time period will increase more areawide rain
probabilities. A more typical weekend trade wind pattern, along
with the southern branch of the polar jet racing across the state,
may enhance late week and weekend shower activity. A higher
frequency of overnight showers that will produce greater rainfall
accumulations along windward exposures and at higher elevation.
&&
.AVIATION...
A trough drifting southward into the area has disrupted the
trades, supporting the light and variable winds continuing
through Tuesday. Expect a gradual clearing pattern through the
evening hours for the smaller islands, then later tonight over the
Big Island as the land breezes become established. The leading
edge of a low cloud band associated with this trough should reach
Kauai overnight, then stall through the day Tuesday. This could
lead to MVFR CIGs/VSBYs in clouds and showers later tonight and
into Tuesday. As a result, the current AIRMET Sierra for MTN OBSC
in place for Kauai may need to be extended later on this evening,
depending how this approaching cloud band evolves. Elsewhere, VFR
conditions will prevail.
&&
.MARINE...
Light and variable winds will prevail through Tuesday as a trough
approaches and stalls near Kauai. The trough will shift westward
Wednesday and Thursday, allowing trades to return and gradually
strengthen. High pressure building northeast of the state will
bring fresh to strong trades back Friday through the upcoming
weekend.
A moderate, short to medium-period north swell will build
tonight, peak late Tuesday through early Wednesday, then gradually
decline through the end of the work week. North shore surf will
return to mostly flat levels over the weekend. The lack of strong
trades over and upstream of the state will keep east shore surf
tiny through mid-week, aside from the locations exposed to the
previously mentioned north swell. The return of fresh to strong
trades will allow east shore surf to gradually build back to near
normal levels Thursday through the weekend. South shore surf will
remain small this week, with mainly background swells moving
through. A small, long-period south-southwest swell could give
south shore surf a boost over the weekend.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Blood
AVIATION...Gibbs
MARINE...Jelsema
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office
Narrow the Menu List
Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit
Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special
Hawaiian Islands Synoptic Discussion and Guidance
949
FXHW60 PHFO 100744 CCA
AFDHFO
Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
944 PM HST Mon Sep 9 2024
.SYNOPSIS...
Large scale light breezes have allowed daytime sea breezes and
nocturnal land breezes to dominate the island's near term wind
regime. These localized onshore breezes will introduce more
interior afternoon cloud build up with isolated showers to be
followed by overnight clear skies. A stalled weak boundary draped
across the northwest waters will assist in producing more showers
around Kauai before dissipating later Tuesday into Wednesday.
Trade winds will return Thursday and strengthen through the
weekend.
&&
.DISCUSSION...
A near stationary 1005 mb surface low approximately 750 miles
northeast of Oahu will be slowly retrograding southwest...its
stalled appendant trough over the north offshore waters about 100
miles north northeast of Kauai. This has created a col in the
regional pressure field thus suppressing the pressure gradient
back to islands from a large area of surface high pressure located
over 1,300 miles northwest of the state. Today's 00Z soundings
still depict a strong near 6k ft inversion with slightly higher
total precipitable waters focused along the west end where
moisture is pooling along the weak boundary north of Kauai. IR
satellite shows the most dense warm cloud cover hanging along this
boundary. Only weak radar returns from light shower activity
around the Garden Isle and Niihau moving south of the tail end of
the trough. As in previous nights within this very light synoptic
scale flow, expect starry skies as mauka drainage winds scour out
the majority of lingering late day clouds. The exceptions may be
along high elevation ridge lines and leeward Big Island zones
where low level moisture tends to get trapped below the inversion.
Higher moisture pooling along this weak meandering trough will not
only be the impetus to statewide light and variable winds but to
higher west state rain chances the next day or so. A diurnal
inland-pushing sea breeze boundary will initiate more Big Island
Kona region showers during the warmth of the afternoon. While the
vertical profile remains relatively dry in the middle and upper
levels over the eastern half of the state just downstream of this
boundary, the near surface boundary layer will remain moist enough
to keep days still feeling a touch more humid than normal as
lower elevations warm into the middle 80s.
The well-stacked upper level low in association with the
aforementioned surface low will begin to fill in and weaken into
an open wave trough as it slowly drifts off to the northwest
through Wednesday. The lack of any upper support will have the
surface trough washing out by Thursday. This will allow the
return of breezy trades from Thursday afternoon into the weekend.
A strong mid-level ridge will continue to support a stable, dry
and warm Central Pacific atmosphere through Thursday. As the upper
low sinks south and weakens upper ridging over the state later
this week, regional heights will subtly fall as mid levels
slightly cool. Higher east mid level moisture advecting into the
area during this time period will increase more areawide rain
probabilities. A more typical weekend trade wind pattern, along
with the southern branch of the polar jet racing across the state,
may enhance late week and weekend shower activity. A higher
frequency of overnight showers that will produce greater rainfall
accumulations along windward exposures and at higher elevation.
&&
.AVIATION...
A trough drifting southward into the area has disrupted the
trades, supporting the light and variable winds continuing
through Tuesday. Expect a gradual clearing pattern through the
evening hours for the smaller islands, then later tonight over the
Big Island as the land breezes become established. The leading
edge of a low cloud band associated with this trough should reach
Kauai overnight, then stall through the day Tuesday. This could
lead to MVFR CIGs/VSBYs in clouds and showers later tonight and
into Tuesday. As a result, the current AIRMET Sierra for MTN OBSC
in place for Kauai may need to be extended later on this evening,
depending how this approaching cloud band evolves. Elsewhere, VFR
conditions will prevail.
&&
.MARINE...
Light and variable winds will prevail through Tuesday as a trough
approaches and stalls near Kauai. The trough will shift westward
Wednesday and Thursday, allowing trades to return and gradually
strengthen. High pressure building northeast of the state will
bring fresh to strong trades back Friday through the upcoming
weekend.
A moderate, short to medium-period north swell will build
tonight, peak late Tuesday through early Wednesday, then gradually
decline through the end of the work week. North shore surf will
return to mostly flat levels over the weekend. The lack of strong
trades over and upstream of the state will keep east shore surf
tiny through mid-week, aside from the locations exposed to the
previously mentioned north swell. The return of fresh to strong
trades will allow east shore surf to gradually build back to near
normal levels Thursday through the weekend. South shore surf will
remain small this week, with mainly background swells moving
through. A small, long-period south-southwest swell could give
south shore surf a boost over the weekend.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Blood
AVIATION...Gibbs
MARINE...Jelsema
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office