NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
316
FXHW60 PHFO 160721
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
921 PM HST Wed May 15 2024
.SYNOPSIS...
Southerly kona winds will continue pulling up unstable tropical
moisture from the deep tropics over the next several days. A kona
low remains in place roughly 600 miles north to northwest of the
Hawaiian Islands as a weakening cold front begins to move into
Kauai. Bands of showers producing moderate to heavy rain and
thunderstorms will develop in this tropical air mass and affect
most islands through Friday. The kona low will begin to drift
away from the state this weekend with improving trends over the
western islands into the upcoming weekend. By Monday all islands
will see a dramatic improvement in weather conditions as the
system moves farther northward.
&&
.DISCUSSION...
In the larger scale, satellite imagery this evening shows a kona
low system roughly 600 miles north to northwest of the Hawaiian
Islands with a weakening cold frontal trough moving into the
islands of Kauai and Niihau from the northwest. Southerly winds
ahead of this system has pulled up deep unstable tropical
moisture over the islands. A combination of local radar and
satellite imagery show convective shower bands forming south of
the western islands. These shower bands will intensify through the
overnight hours with periods of heavy rain expected to fall across
much of the state. Soil moisture remains saturated for most areas,
which means any additional heavy rainfall could swiftly turn into
runoff and a threat for flash flooding. For these reasons a Flood
Watch remains in effect for most of the state. The flood threat
for the Big Island remains at a lower threat level at this time,
therefore the Big Island is no longer in the Flood Watch.
Kauai County and Oahu weather impacts...The cold front moving
into Kauai County by early Thursday morning will combine forces
with the unstable tropical air mass over the next several days.
Increasing low level convergence along the frontal trough will
help to lift the unstable moisture over the mountain slopes of
Kauai and Oahu, increasing the threat for flooding due to
moderate to heavy showers and thunderstorms potentially training
over the island. A deep plume of tropical moisture, with showers
and thunderstorms, will linger over Kauai County and Oahu through
Friday. Medium range forecast guidance show drier and more stable
southeasterly winds building in with the ridge as the kona low
drifts northward from Friday night into Saturday morning. Any
small delay in the ridge building back in will slow down these
improving weather trends this weekend.
Maui County weather impacts...Deep tropical moisture in southerly
kona winds will produce bands of moderate to heavy showers over
the islands of Maui County over the next few days. The main
threats for Maui County will be if these storms line up over any
one location potentially producing 1 to 2 inches per hour rainfall
for several hours. These small scale convective shower bands are
notoriously hard to predict well in advance. These areas in Maui
County often see fair conditions rapidly deteriorate into heavy
rain with rapid runoff and flooding in a very short time period.
Big Island weather impacts...Tropical moisture will affect the Big
Island into Friday. The southeastern slopes of the Big Island
would be in the highest threat level for heavy rain during this
event. Most of the deep convective showers should remain west of
the Big Island this week with just a slight risk of flooding over
Hawaii County.
Sunday through Monday...We transition back to a drier weather
pattern as high pressure builds in from the east producing a
drier and more stable southeasterly wind flow pattern across the
Hawaii region as the kona low drift farther northward away from
the state.
&&
.AVIATION...
A strengthening kona low about 650 nm northwest of Kauai is
pulling tropical moisture out of the south southeast across the
state. This will keep the Hawaiian Islands in an active weather
pattern through the remainder of the week. Moderate to heavy
showers and possible thunderstorms are expected over the smaller
islands through twenty-four hours and beyond. On the Big Island,
shower activity is expected to be greatest in the afternoon and
early evening hours.
Latest radar imagery reveals a broad band of vigorous showers
streaming across Oahu and Kauai from the south. This band is
expected to shift slowly eastward, spreading across Maui county by
tomorrow afternoon.
AIRMET Sierra is in effect for all of the smaller islands and
windward Big Island for mountain obscuration. Sierra may be
needed for IFR conds later tonight.
AIRMET Tango is in effect for the entire area for mod turb btn
FL300 and FL400. Tango may also been needed for mechanical
turbulence below 08kft as the kona low gets closer and conditions
deteriorate overnight.
&&
.MARINE...
Fresh to locally strong south to southeast winds will persist
through Friday for most waters, with a shift out of the east to
southeast direction over the weekend through early next week as a
kona low meanders north-northwest of the state. As a result, a
Small Craft Advisory will likely be issued later tonight for the
coastal waters that experience wind accelerations with this
direction (Hamakua Coast and waters around South Point of the Big
Island). In addition to the winds, expect locally rough seas in
heavy showers or storms that develop over the next few days, with
the best chances being over the waters west of Maui County.
Surf along south facing shores will remain up through early next
week due to overlapping, long-period south-southwest swells
expected. The first will rise through the day Thursday, then peak
Friday, likely at the advisory level. Expect rough conditions for
most southerly exposures through this period due to the onshore
winds and periodic heavy showers moving through. As this swell
slowly eases over the weekend, a fresh, long-period south-
southwest swell will begin to fill in through the day Sunday. This
will peak early next week before easing through midweek.
Surf along north and west facing shores will trend up Thursday,
linger into Friday, then ease through the weekend as a short-
period northwest swell from the nearby kona low moves through.
Surf along east facing shores will remain well below average
through the weekend. An upward trend is possible next week as the
trades return locally and far upstream over the eastern Pacific.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday evening for the islands of Kauai
County, Oahu and Maui County.
Wind Advisory until 4 AM HST Thursday for Big Island Summits.
&&
$$
DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Gibbs
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office
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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
316
FXHW60 PHFO 160721
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
921 PM HST Wed May 15 2024
.SYNOPSIS...
Southerly kona winds will continue pulling up unstable tropical
moisture from the deep tropics over the next several days. A kona
low remains in place roughly 600 miles north to northwest of the
Hawaiian Islands as a weakening cold front begins to move into
Kauai. Bands of showers producing moderate to heavy rain and
thunderstorms will develop in this tropical air mass and affect
most islands through Friday. The kona low will begin to drift
away from the state this weekend with improving trends over the
western islands into the upcoming weekend. By Monday all islands
will see a dramatic improvement in weather conditions as the
system moves farther northward.
&&
.DISCUSSION...
In the larger scale, satellite imagery this evening shows a kona
low system roughly 600 miles north to northwest of the Hawaiian
Islands with a weakening cold frontal trough moving into the
islands of Kauai and Niihau from the northwest. Southerly winds
ahead of this system has pulled up deep unstable tropical
moisture over the islands. A combination of local radar and
satellite imagery show convective shower bands forming south of
the western islands. These shower bands will intensify through the
overnight hours with periods of heavy rain expected to fall across
much of the state. Soil moisture remains saturated for most areas,
which means any additional heavy rainfall could swiftly turn into
runoff and a threat for flash flooding. For these reasons a Flood
Watch remains in effect for most of the state. The flood threat
for the Big Island remains at a lower threat level at this time,
therefore the Big Island is no longer in the Flood Watch.
Kauai County and Oahu weather impacts...The cold front moving
into Kauai County by early Thursday morning will combine forces
with the unstable tropical air mass over the next several days.
Increasing low level convergence along the frontal trough will
help to lift the unstable moisture over the mountain slopes of
Kauai and Oahu, increasing the threat for flooding due to
moderate to heavy showers and thunderstorms potentially training
over the island. A deep plume of tropical moisture, with showers
and thunderstorms, will linger over Kauai County and Oahu through
Friday. Medium range forecast guidance show drier and more stable
southeasterly winds building in with the ridge as the kona low
drifts northward from Friday night into Saturday morning. Any
small delay in the ridge building back in will slow down these
improving weather trends this weekend.
Maui County weather impacts...Deep tropical moisture in southerly
kona winds will produce bands of moderate to heavy showers over
the islands of Maui County over the next few days. The main
threats for Maui County will be if these storms line up over any
one location potentially producing 1 to 2 inches per hour rainfall
for several hours. These small scale convective shower bands are
notoriously hard to predict well in advance. These areas in Maui
County often see fair conditions rapidly deteriorate into heavy
rain with rapid runoff and flooding in a very short time period.
Big Island weather impacts...Tropical moisture will affect the Big
Island into Friday. The southeastern slopes of the Big Island
would be in the highest threat level for heavy rain during this
event. Most of the deep convective showers should remain west of
the Big Island this week with just a slight risk of flooding over
Hawaii County.
Sunday through Monday...We transition back to a drier weather
pattern as high pressure builds in from the east producing a
drier and more stable southeasterly wind flow pattern across the
Hawaii region as the kona low drift farther northward away from
the state.
&&
.AVIATION...
A strengthening kona low about 650 nm northwest of Kauai is
pulling tropical moisture out of the south southeast across the
state. This will keep the Hawaiian Islands in an active weather
pattern through the remainder of the week. Moderate to heavy
showers and possible thunderstorms are expected over the smaller
islands through twenty-four hours and beyond. On the Big Island,
shower activity is expected to be greatest in the afternoon and
early evening hours.
Latest radar imagery reveals a broad band of vigorous showers
streaming across Oahu and Kauai from the south. This band is
expected to shift slowly eastward, spreading across Maui county by
tomorrow afternoon.
AIRMET Sierra is in effect for all of the smaller islands and
windward Big Island for mountain obscuration. Sierra may be
needed for IFR conds later tonight.
AIRMET Tango is in effect for the entire area for mod turb btn
FL300 and FL400. Tango may also been needed for mechanical
turbulence below 08kft as the kona low gets closer and conditions
deteriorate overnight.
&&
.MARINE...
Fresh to locally strong south to southeast winds will persist
through Friday for most waters, with a shift out of the east to
southeast direction over the weekend through early next week as a
kona low meanders north-northwest of the state. As a result, a
Small Craft Advisory will likely be issued later tonight for the
coastal waters that experience wind accelerations with this
direction (Hamakua Coast and waters around South Point of the Big
Island). In addition to the winds, expect locally rough seas in
heavy showers or storms that develop over the next few days, with
the best chances being over the waters west of Maui County.
Surf along south facing shores will remain up through early next
week due to overlapping, long-period south-southwest swells
expected. The first will rise through the day Thursday, then peak
Friday, likely at the advisory level. Expect rough conditions for
most southerly exposures through this period due to the onshore
winds and periodic heavy showers moving through. As this swell
slowly eases over the weekend, a fresh, long-period south-
southwest swell will begin to fill in through the day Sunday. This
will peak early next week before easing through midweek.
Surf along north and west facing shores will trend up Thursday,
linger into Friday, then ease through the weekend as a short-
period northwest swell from the nearby kona low moves through.
Surf along east facing shores will remain well below average
through the weekend. An upward trend is possible next week as the
trades return locally and far upstream over the eastern Pacific.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday evening for the islands of Kauai
County, Oahu and Maui County.
Wind Advisory until 4 AM HST Thursday for Big Island Summits.
&&
$$
DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Gibbs
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office