NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
488
FXHW60 PHFO 130642
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
842 PM HST Wed Aug 12 2026
.SYNOPSIS...
Increased trade winds Thursday and Friday combined with dry
conditions will elevate the fire weather threat for the end of the
work week. Most likely locations for any occasional showers will
be over the windward and mauka areas through Friday. For the
weekend, we're continuing to monitor Potential Tropical Cyclone
One-C. Residents and visitors should prepare now for potential
tropical cyclone impacts this weekend. Please monitor
www.hurricanes.gov for the latest information.
&&
.UPDATE...
Issued at 835 PM HST Wed Aug 12 2026
This evening, the previous forecast remains largely in tact. Latest
satellite and radar imagery shows a few areas of low clouds and
showers embedded within the trade winds moving into windward and
mauka areas. Expect these to continue throughout the night, with
some improvement expected again during the morning hours Thursday.
Meanwhile, episode 53 of lava fountaining in Halema'uma'u at the
summit of Kilauea began at 345pm HST. Following the beginning of
episode 53, a plume of moderate tephra and gas was observed up to
around 18,000 ft ASL, moving southwest in lower levels and more
westerly in higher levels. As of 830pm HST this evening, the plume
height has decreased a bit, but GOES Ash RGB satellite imagery
shows the plume moving west-northwest across the Big Island.
Fountaining episodes typically last less than 12 hours, but ash
can remain in the air longer depending on wind and weather. See
the latest Special Weather Statement (SPS) for more detailed
information.
As previous forecast discussions have mentioned, the main forecast
concern for the next few days remains the development of Potential
Tropical Cyclone One-C. In anticipation of critical new updates with
each of the next few advisory packages issued by the National
Hurricane Center (NHC), the NWS Honolulu will begin delaying the
issuance of our typical forecast package products starting Thursday
morning (AFD, SFT, PFM, ZFP, SPF, CWF, etc.) until after the
release of NHC's suite of products to incorporate the latest and
most up-to-date information on Potential Tropical Cyclone One-C.
&&
.PREV DISCUSSION...
Issued at 356 PM HST Wed Aug 12 2026
At 3 PM, satellite imagery was indicating most of the shower
activity was focused on Maui and Molokai with rainfall gauges
showing 0.10" or less of accumulated rain over the last 3 hours.
Occasional light showers are expected to continue through the rest
of this afternoon and evening. Mostly dry conditions are expected to
continue through the rest of the work week. Those in windward and
mauka areas will continue to see scattered showers at times through
Friday.
The main forecast concern for late Friday through the weekend will
be the development of Potential Tropical Cyclone One-C. The system
has not moved much since this morning and is still about 900 miles
east-southeast of the Big Island. There have only been minor changes
to the forecast since this morning, with the National Hurricane
Center still forecasting it to develop into a Tropical Storm as
early as tomorrow morning. The details of the forecast are still
uncertain but impacts are expected to the state as early as Friday
night and will continue through the weekend. Interests within the
main Hawaiian Islands should closely monitor for forecast updates
and prepare for the potential impacts described below.
FIRE WEATHER... Fire weather concerns will increase on Friday ahead
of any potential tropical cyclone's arrival. Winds will begin to
strengthen while a dry and stable air mass with low relative
humidity moves overhead. This combination of lower relative humidity
and increasing wind speeds will likely lead to high wildfire risk.
STRONG AND GUSTY WINDS... Winds could strengthen further on
Saturday, though the timing, direction, and magnitude of the
strongest winds remain highly dependent on the eventual track and
intensity of the system. Even if the center of the system remains
away from the islands, the north semicircle of the storm will likely
produce damaging winds. Due to the great uncertainty at this time,
it is likely that the current deterministic forecast is under-doing
winds at some locations, while potentially over-doing the winds at
others. The specifics on winds impacts will become more clear as
further development occurs over the next 24 to 48 hours.
HEAVY RAINFALL... This system could bring periods of heavy rainfall,
particularly across east and southeast-facing slopes. Orographic
enhancement could result in locally higher rainfall totals where
moist tropical flow interacts with island terrain. If heavier
rainfall persists over the same locations, flash flooding and
rapidly rising streams are possible. Again, the location of heaviest
rain and any bands that would move through the islands will be
highly dependent on the system's track. Current forecast has 5-10
inches of rain with locally higher amounts Friday through the
weekend. Heavy rainfall is currently forecast to impact the Big
Island as early as Friday, spreading to Maui on Saturday, and Lanai,
Molokai, Oahu, and Kauai on Sunday.
LARGE AND ROUGH SURF... The developing system is expected to
generate a large easterly swell as it moves northwestward across the
Central Pacific. Surf may build along east-facing shores from east
to west as the system approaches, with warning level surf of 15 feet
or larger possible into the weekend.
&&
.AVIATION...
Breezy trade winds will gradually strengthen through Friday.
Scattered showers will focus over mostly windward and mountain
areas, especially during the evening/overnight hours. Some showers
will spill over to leeward areas. Expect mostly VFR during the
day with periods of MVFR especially during the overnight and in
showers.
AIRMET Sierra for mountain obscuration may be needed for
windward/mauka locations overnight through Thursday morning as
shower coverage increases. AIRMET Tango may also be needed
overnight or Thursday for moderate turbulence immediately south
and west of mountains due to strengthening low-level winds.
&&
.MARINE...
Issued at 356 PM HST Wed Aug 12 2026
High pressure to the far northeast will slowly drift into a position
just north of the Hawaiian Islands into the weekend, producing
moderate to locally strong trade winds across the region. A Small
Craft Advisory (SCA) remains in place through Thursday afternoon
for the windier waters and channels around Maui and the Big
Island. As the high builds north of the state, the trade winds
will strengthen Thursday into Friday, which will likely cause the
SCA to expand in coverage by Friday.
The weather pattern will change significantly this weekend as we
anticipate the development of Potential Tropical Cyclone One-C,
currently around 700 NM east-southeast of the Big Island.
Marine interests should be prepared for potential tropical
cyclone impacts to offshore and coastal marine zones starting
Friday and lasting through the weekend. Rapidly changing
conditions are expected this weekend, especially across waters
exposed to the Potential Tropical Cyclone One-C winds and swells.
Surf along south and west facing shores will continue to remain
elevated as a new long-period south swell fills in tonight and
peaks on Thursday. A High Surf Advisory (HSA) has been issued for
south facing shores. This south swell energy will then slowly
fade into Saturday and may linger at advisory thresholds into
Friday. Another small reinforcement is expected late Sunday into
Monday out of the south.
Surf along east facing shores will continue to remain moderate
and choppy due to continued moderate to locally breezy trade
winds. Swells from Potential Tropical Cyclone One-C could begin
arriving as early as Friday, but the main energy from the
Potential Tropical Cyclone will likely arrive this weekend and
should produce surf heights exceeding warning levels along east
facing shores. Based on the current forecast from the National
Hurricane Center, dangerous surf conditions are expected around
Maui and the Big Island on Saturday and around Oahu and Kauai
Saturday night into Sunday.
&&
.FIRE WEATHER...
Issued at 356 PM HST Wed Aug 12 2026
Moderate to locally breezy trade winds and a pocket of drier air is
expected to remain in place through Thursday, which will lower
afternoon humidities. The moderate to locally breezy winds combined
with drier air will raise fire weather concerns. Fire weather
conditions may become near-critical by Friday due to increased trade
winds and dry air still in place. Temperature inversion heights will
range between 4,500 to 6,000 feet over the next few days.
Relative humidity is expected to increase over the weekend due to
the incoming tropical system.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Big Island South-
Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro-
Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai
South-Maui Central Valley South-Maui Leeward West-Molokai
Leeward South-Molokai West-Niihau-South Haleakala-South
Maui/Upcountry-Waianae Coast.
Small Craft Advisory until 6 PM HST Thursday for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters-
Maalaea Bay-Pailolo Channel.
&&
$$
UPDATE...Vaughan
DISCUSSION...CO
AVIATION...Munroe
MARINE...Kino
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
488
FXHW60 PHFO 130642
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
842 PM HST Wed Aug 12 2026
.SYNOPSIS...
Increased trade winds Thursday and Friday combined with dry
conditions will elevate the fire weather threat for the end of the
work week. Most likely locations for any occasional showers will
be over the windward and mauka areas through Friday. For the
weekend, we're continuing to monitor Potential Tropical Cyclone
One-C. Residents and visitors should prepare now for potential
tropical cyclone impacts this weekend. Please monitor
www.hurricanes.gov for the latest information.
&&
.UPDATE...
Issued at 835 PM HST Wed Aug 12 2026
This evening, the previous forecast remains largely in tact. Latest
satellite and radar imagery shows a few areas of low clouds and
showers embedded within the trade winds moving into windward and
mauka areas. Expect these to continue throughout the night, with
some improvement expected again during the morning hours Thursday.
Meanwhile, episode 53 of lava fountaining in Halema'uma'u at the
summit of Kilauea began at 345pm HST. Following the beginning of
episode 53, a plume of moderate tephra and gas was observed up to
around 18,000 ft ASL, moving southwest in lower levels and more
westerly in higher levels. As of 830pm HST this evening, the plume
height has decreased a bit, but GOES Ash RGB satellite imagery
shows the plume moving west-northwest across the Big Island.
Fountaining episodes typically last less than 12 hours, but ash
can remain in the air longer depending on wind and weather. See
the latest Special Weather Statement (SPS) for more detailed
information.
As previous forecast discussions have mentioned, the main forecast
concern for the next few days remains the development of Potential
Tropical Cyclone One-C. In anticipation of critical new updates with
each of the next few advisory packages issued by the National
Hurricane Center (NHC), the NWS Honolulu will begin delaying the
issuance of our typical forecast package products starting Thursday
morning (AFD, SFT, PFM, ZFP, SPF, CWF, etc.) until after the
release of NHC's suite of products to incorporate the latest and
most up-to-date information on Potential Tropical Cyclone One-C.
&&
.PREV DISCUSSION...
Issued at 356 PM HST Wed Aug 12 2026
At 3 PM, satellite imagery was indicating most of the shower
activity was focused on Maui and Molokai with rainfall gauges
showing 0.10" or less of accumulated rain over the last 3 hours.
Occasional light showers are expected to continue through the rest
of this afternoon and evening. Mostly dry conditions are expected to
continue through the rest of the work week. Those in windward and
mauka areas will continue to see scattered showers at times through
Friday.
The main forecast concern for late Friday through the weekend will
be the development of Potential Tropical Cyclone One-C. The system
has not moved much since this morning and is still about 900 miles
east-southeast of the Big Island. There have only been minor changes
to the forecast since this morning, with the National Hurricane
Center still forecasting it to develop into a Tropical Storm as
early as tomorrow morning. The details of the forecast are still
uncertain but impacts are expected to the state as early as Friday
night and will continue through the weekend. Interests within the
main Hawaiian Islands should closely monitor for forecast updates
and prepare for the potential impacts described below.
FIRE WEATHER... Fire weather concerns will increase on Friday ahead
of any potential tropical cyclone's arrival. Winds will begin to
strengthen while a dry and stable air mass with low relative
humidity moves overhead. This combination of lower relative humidity
and increasing wind speeds will likely lead to high wildfire risk.
STRONG AND GUSTY WINDS... Winds could strengthen further on
Saturday, though the timing, direction, and magnitude of the
strongest winds remain highly dependent on the eventual track and
intensity of the system. Even if the center of the system remains
away from the islands, the north semicircle of the storm will likely
produce damaging winds. Due to the great uncertainty at this time,
it is likely that the current deterministic forecast is under-doing
winds at some locations, while potentially over-doing the winds at
others. The specifics on winds impacts will become more clear as
further development occurs over the next 24 to 48 hours.
HEAVY RAINFALL... This system could bring periods of heavy rainfall,
particularly across east and southeast-facing slopes. Orographic
enhancement could result in locally higher rainfall totals where
moist tropical flow interacts with island terrain. If heavier
rainfall persists over the same locations, flash flooding and
rapidly rising streams are possible. Again, the location of heaviest
rain and any bands that would move through the islands will be
highly dependent on the system's track. Current forecast has 5-10
inches of rain with locally higher amounts Friday through the
weekend. Heavy rainfall is currently forecast to impact the Big
Island as early as Friday, spreading to Maui on Saturday, and Lanai,
Molokai, Oahu, and Kauai on Sunday.
LARGE AND ROUGH SURF... The developing system is expected to
generate a large easterly swell as it moves northwestward across the
Central Pacific. Surf may build along east-facing shores from east
to west as the system approaches, with warning level surf of 15 feet
or larger possible into the weekend.
&&
.AVIATION...
Breezy trade winds will gradually strengthen through Friday.
Scattered showers will focus over mostly windward and mountain
areas, especially during the evening/overnight hours. Some showers
will spill over to leeward areas. Expect mostly VFR during the
day with periods of MVFR especially during the overnight and in
showers.
AIRMET Sierra for mountain obscuration may be needed for
windward/mauka locations overnight through Thursday morning as
shower coverage increases. AIRMET Tango may also be needed
overnight or Thursday for moderate turbulence immediately south
and west of mountains due to strengthening low-level winds.
&&
.MARINE...
Issued at 356 PM HST Wed Aug 12 2026
High pressure to the far northeast will slowly drift into a position
just north of the Hawaiian Islands into the weekend, producing
moderate to locally strong trade winds across the region. A Small
Craft Advisory (SCA) remains in place through Thursday afternoon
for the windier waters and channels around Maui and the Big
Island. As the high builds north of the state, the trade winds
will strengthen Thursday into Friday, which will likely cause the
SCA to expand in coverage by Friday.
The weather pattern will change significantly this weekend as we
anticipate the development of Potential Tropical Cyclone One-C,
currently around 700 NM east-southeast of the Big Island.
Marine interests should be prepared for potential tropical
cyclone impacts to offshore and coastal marine zones starting
Friday and lasting through the weekend. Rapidly changing
conditions are expected this weekend, especially across waters
exposed to the Potential Tropical Cyclone One-C winds and swells.
Surf along south and west facing shores will continue to remain
elevated as a new long-period south swell fills in tonight and
peaks on Thursday. A High Surf Advisory (HSA) has been issued for
south facing shores. This south swell energy will then slowly
fade into Saturday and may linger at advisory thresholds into
Friday. Another small reinforcement is expected late Sunday into
Monday out of the south.
Surf along east facing shores will continue to remain moderate
and choppy due to continued moderate to locally breezy trade
winds. Swells from Potential Tropical Cyclone One-C could begin
arriving as early as Friday, but the main energy from the
Potential Tropical Cyclone will likely arrive this weekend and
should produce surf heights exceeding warning levels along east
facing shores. Based on the current forecast from the National
Hurricane Center, dangerous surf conditions are expected around
Maui and the Big Island on Saturday and around Oahu and Kauai
Saturday night into Sunday.
&&
.FIRE WEATHER...
Issued at 356 PM HST Wed Aug 12 2026
Moderate to locally breezy trade winds and a pocket of drier air is
expected to remain in place through Thursday, which will lower
afternoon humidities. The moderate to locally breezy winds combined
with drier air will raise fire weather concerns. Fire weather
conditions may become near-critical by Friday due to increased trade
winds and dry air still in place. Temperature inversion heights will
range between 4,500 to 6,000 feet over the next few days.
Relative humidity is expected to increase over the weekend due to
the incoming tropical system.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Big Island South-
Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro-
Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai
South-Maui Central Valley South-Maui Leeward West-Molokai
Leeward South-Molokai West-Niihau-South Haleakala-South
Maui/Upcountry-Waianae Coast.
Small Craft Advisory until 6 PM HST Thursday for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters-
Maalaea Bay-Pailolo Channel.
&&
$$
UPDATE...Vaughan
DISCUSSION...CO
AVIATION...Munroe
MARINE...Kino
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office