NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
950
FXHW60 PHFO 231337
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
337 AM HST Fri May 23 2025
.SYNOPSIS...
High pressure far to our northwest will keep breezy trades blowing
through Sunday, with the trades gradually easing next week as the
high weakens. An upper level low near the islands will help to
enhance showers today and tonight. As the upper low moves away
over the holiday weekend, drier and more stable air will return to
the Aloha State, with fewer showers and lots of sunshine expected.
&&
.DISCUSSION...
A relatively strong and large 1035 mb surface high is still
centered roughly 1200 mi NNW of Kauai. This high has been
meandering around in the same general area for the past few days,
giving us breezy trades. Meanwhile, a mid- to upper-level low is
located on water vapor imagery only about 100 mi N of Oahu.
The GOES-derived CAPE shows a pocket of significant instability
associated with this low aloft which is validated by the 12z
soundings, but so far there have mainly been only TCU associated
with it, due in part to the breezy trades hindering updraft
development. The only lightning detected by the GLM or NLDN
overnight has actually been from a couple of brief CB that were
located 60-100 mi S of Kauai and Oahu, in the downwind
convergence zones from the wind shadow of the islands.
Guidance shows this upper low will start to lift slowly NE away
from the islands today, gradually taking its pocket of cold air
aloft and instability with it. Since the trades are expected to
continue breezy, it is very tempting to remove the slight chance
thunder from our forecast altogether, but have reluctantly left
it in for Kauai for the morning in deference to local guidance and
a disorganized band of moisture expected to move through today. We
will also leave a slight chance of thunder over the interior
slopes of the Big Island for this afternoon, where we have seen a
lone thundershower pop up on the slopes of Mauna Loa the last
couple of afternoons.
Fine weather is expected for most of the holiday weekend, with any
lingering enhancement to incoming trade wind showers fading away
on Sat. In fact, models show quite low PW for late May pushing in
Sat night, with values maybe even dropping below 1 inch early
next week. Although PW increases significantly over the islands
toward the middle of the week, forecast soundings show that this
PW is largely from abundant high- and mid-level moisture being
drawn up by the jet stream from deep convection in the ITCZ far
south of the islands, while maintaining a dry and stable boundary
layer over us. Thus we are indicating an increase in clouds in the
forecast, but not a lot of trade wind rainfall late in the
forecast period.
Trade winds should remain breezy over the islands through about
Sunday, then start trending downward on Memorial Day as the high
gradually shifts south, weakens, and elongates across most of the
eastern Pacific becoming a rather weak subtropical ridge by about
Wed or Thu when gentle trades are expected, staying locally
breezy only in the normal windiest spots.
&&
.AVIATION...
An upper low near the main Hawaiian Islands will continue to
enhance incoming trade wind clouds and SHRA. TEMPO MVFR ceilings
and vis can be expected in any SHRA, and can't rule out isolated
TSRA mainly near or over Kauai this AM. AIRMET for MTN OBSC may be
needed for windward N and E facing slopes. Overall conditions
should gradually improve later today with shower coverage and
intensity diminishing as the upper low begins to move away. Trade
winds will remain breezy for the next few days.
&&
.MARINE...
No significant changes to the forecast with the morning package.
High pressure off to the distant north-northwest will maintain
moderate to locally strong trade winds through the weekend. The
high is expected to weaken early next week, with winds near the
islands settling back into the moderate to fresh levels. An upper
level low lingering near the state today will help to enhance trade
wind showers, and could bring the potential for isolated
thunderstorms, mainly over Kauai and Oahu waters. A Small Craft
Advisory for the windier waters and channels around Maui County
and the Big Island has been extended through early Saturday
morning.
Surf along south facing shores will gradually build today through
Saturday as a long period south-southwest swell is expected to
fill in, producing near seasonal average surf through the weekend
before declining early next week. Another long-period south-
southwest swell is expected to arrive Wednesday into Thursday,
bringing more near seasonal average surf to south facing shores.
East shore surf will remain near seasonal average through the weekend
as trade winds persist, then gradually decline into midweek as the
trades weaken slightly.
Tiny surf will prevail along north facing shores through early next
week. A small to moderate medium period northwest swell will arrive
late Wednesday into Thursday of next week, bringing above seasonal
average surf.
Starting Saturday and lasting into Wednesday, we can expect
higher than normal tides, which could lead to some coastal
flooding during the peak of high tides in the early afternoon
hours. As this elevated tide is expected between the 2 south
period swells, it looks like this event will have minimal impact.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
&&
$$
DISCUSSION and AVIATION...R Ballard
MARINE...M Ballard
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
950
FXHW60 PHFO 231337
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
337 AM HST Fri May 23 2025
.SYNOPSIS...
High pressure far to our northwest will keep breezy trades blowing
through Sunday, with the trades gradually easing next week as the
high weakens. An upper level low near the islands will help to
enhance showers today and tonight. As the upper low moves away
over the holiday weekend, drier and more stable air will return to
the Aloha State, with fewer showers and lots of sunshine expected.
&&
.DISCUSSION...
A relatively strong and large 1035 mb surface high is still
centered roughly 1200 mi NNW of Kauai. This high has been
meandering around in the same general area for the past few days,
giving us breezy trades. Meanwhile, a mid- to upper-level low is
located on water vapor imagery only about 100 mi N of Oahu.
The GOES-derived CAPE shows a pocket of significant instability
associated with this low aloft which is validated by the 12z
soundings, but so far there have mainly been only TCU associated
with it, due in part to the breezy trades hindering updraft
development. The only lightning detected by the GLM or NLDN
overnight has actually been from a couple of brief CB that were
located 60-100 mi S of Kauai and Oahu, in the downwind
convergence zones from the wind shadow of the islands.
Guidance shows this upper low will start to lift slowly NE away
from the islands today, gradually taking its pocket of cold air
aloft and instability with it. Since the trades are expected to
continue breezy, it is very tempting to remove the slight chance
thunder from our forecast altogether, but have reluctantly left
it in for Kauai for the morning in deference to local guidance and
a disorganized band of moisture expected to move through today. We
will also leave a slight chance of thunder over the interior
slopes of the Big Island for this afternoon, where we have seen a
lone thundershower pop up on the slopes of Mauna Loa the last
couple of afternoons.
Fine weather is expected for most of the holiday weekend, with any
lingering enhancement to incoming trade wind showers fading away
on Sat. In fact, models show quite low PW for late May pushing in
Sat night, with values maybe even dropping below 1 inch early
next week. Although PW increases significantly over the islands
toward the middle of the week, forecast soundings show that this
PW is largely from abundant high- and mid-level moisture being
drawn up by the jet stream from deep convection in the ITCZ far
south of the islands, while maintaining a dry and stable boundary
layer over us. Thus we are indicating an increase in clouds in the
forecast, but not a lot of trade wind rainfall late in the
forecast period.
Trade winds should remain breezy over the islands through about
Sunday, then start trending downward on Memorial Day as the high
gradually shifts south, weakens, and elongates across most of the
eastern Pacific becoming a rather weak subtropical ridge by about
Wed or Thu when gentle trades are expected, staying locally
breezy only in the normal windiest spots.
&&
.AVIATION...
An upper low near the main Hawaiian Islands will continue to
enhance incoming trade wind clouds and SHRA. TEMPO MVFR ceilings
and vis can be expected in any SHRA, and can't rule out isolated
TSRA mainly near or over Kauai this AM. AIRMET for MTN OBSC may be
needed for windward N and E facing slopes. Overall conditions
should gradually improve later today with shower coverage and
intensity diminishing as the upper low begins to move away. Trade
winds will remain breezy for the next few days.
&&
.MARINE...
No significant changes to the forecast with the morning package.
High pressure off to the distant north-northwest will maintain
moderate to locally strong trade winds through the weekend. The
high is expected to weaken early next week, with winds near the
islands settling back into the moderate to fresh levels. An upper
level low lingering near the state today will help to enhance trade
wind showers, and could bring the potential for isolated
thunderstorms, mainly over Kauai and Oahu waters. A Small Craft
Advisory for the windier waters and channels around Maui County
and the Big Island has been extended through early Saturday
morning.
Surf along south facing shores will gradually build today through
Saturday as a long period south-southwest swell is expected to
fill in, producing near seasonal average surf through the weekend
before declining early next week. Another long-period south-
southwest swell is expected to arrive Wednesday into Thursday,
bringing more near seasonal average surf to south facing shores.
East shore surf will remain near seasonal average through the weekend
as trade winds persist, then gradually decline into midweek as the
trades weaken slightly.
Tiny surf will prevail along north facing shores through early next
week. A small to moderate medium period northwest swell will arrive
late Wednesday into Thursday of next week, bringing above seasonal
average surf.
Starting Saturday and lasting into Wednesday, we can expect
higher than normal tides, which could lead to some coastal
flooding during the peak of high tides in the early afternoon
hours. As this elevated tide is expected between the 2 south
period swells, it looks like this event will have minimal impact.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
&&
$$
DISCUSSION and AVIATION...R Ballard
MARINE...M Ballard
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office