NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
190
FXHW60 PHFO 200106
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
306 PM HST Mon May 19 2025
.SYNOPSIS...
Moderate to breezy trades will deliver clouds and showers to
windward and mauka areas through the week. Trades strengthen
slightly beginning Thursday.
&&
.DISCUSSION...
The weak upper low that has lingered around the area during the last
week is presently positioned northeast of the Big Island at 250mb
and roughly over/immediately east of the island at 500mb where the
center is analyzed at 583dm. The islands reside along the southern
periphery of the attendant cold pool and observed 500mb temperatures
are approximately -9C and -10C at Lihue and Hilo respectively as of
12 UTC this morning. This low will sag southeast and tend to deepen
as the mid-latitude pattern eases southward during the next couple
of days. At the same time, energy associated with a progressive mid-
latitude trough will pinch off from the westerlies as it crosses
160W and close off in the vicinity of Kauai during Wednesday. The
islands, residing between these two rather small scale lows, will be
positioned below a narrow band of shortwave ridging aloft Wednesday
into Thursday. Attendant height rises in the mid-levels may
nonetheless be hard to come by as the overall geopotential height
field remains depressed and even further deepens given that the weak
low presently over/east of the Big Island is modeled to deepen to
579dm as it drifts eastward. As a consequence, little change in the
thermodynamic profile is anticipated today into Thursday with the
exception of the aforementioned upper-level ridging helping to quash
afternoon thunder potential over the Big Island. Moderate to locally
breezy trades will remain weakly stable during this time with
pockets of heavier showers developing where low-level convergence is
maximized, mainly Leeward Big Island along the sea breeze each
afternoon. Here, nuisance flooding is not out of the question.
By Thursday, lapse rates steepen to 6.5 to 7.0C/km over the western
end of the state, the GFS being notably colder and unstable aloft
compared to the EC which settles the low further west. Regardless of
the model differences, ridge amplification east of the Dateline will
cause trades to strengthen during this time limiting the potential
for areas of enhanced convergence to emerge anywhere except Leeward
Big Island. As a result, expect some variety of moderately unstable
trades to develop no later than Thursday and continue through at
least Friday night. From a sensible weather perspective, this
suggests quick-moving/transient trade wind showers some of which may
be heavy, especially at night and during the morning. The potential
for thunderstorms over leeward/interior portions of the Big Island
on Thurs/Fri will be evaluated going forward as this area stands the
greatest chance to experience organized heavy rainfall as diurnal
convection develops each afternoon.
&&
.AVIATION...
Trade winds will return to a more easterly direction tonight and
strengthen into the moderate to locally breezy range from Tuesday
onward as the ridge builds in north of the state. Expect passing
showers mainly over windward and mountain areas and along leeward
convergence cloud bands through Tuesday, with brief MVFR conditions
possible within any shower bands. No AIRMETs are currently in
effect.
&&
.MARINE...
Trades will persist through the weekend, with the strongest winds
expected late Wednesday and Thursday. Currently, a 1032 mb
centered nearly 1400 nm northeast of the state is driving moderate
to fresh trade winds. Surface low pressure will form far north of
the islands tonight and push the surface high eastward on
Tuesday. Meanwhile, another area of high pressure from the west
Pacific will move into the central Pacific, then stall far north
of Hawaii on Wednesday into Friday. As the new high moves in,
expect trade winds to increase to fresh to strong levels on
Wednesday or Thursday, when a Small Craft Advisory (SCA) will be
needed for the typically windy waters around the Big Island and
Maui. The high is forecast to retreat westward during the weekend,
favoring a decrease in winds.
Surf along south facing shores will remain just below seasonal
average into Saturday as pulses of south-southwest and southwest
swell move through. Surf will decline Sunday and remain small into
early next week.
East shore surf will remain near or just below seasonal average
during the next couple of days, followed by a slight increase
Thursday and Friday as trade winds build east of the islands. A
gradual decline in east shore surf is expected during the weekend
and early next week. Tiny surf will prevail along north facing
shores this week.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...JVC
AVIATION...TS
MARINE...Wroe
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
190
FXHW60 PHFO 200106
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
306 PM HST Mon May 19 2025
.SYNOPSIS...
Moderate to breezy trades will deliver clouds and showers to
windward and mauka areas through the week. Trades strengthen
slightly beginning Thursday.
&&
.DISCUSSION...
The weak upper low that has lingered around the area during the last
week is presently positioned northeast of the Big Island at 250mb
and roughly over/immediately east of the island at 500mb where the
center is analyzed at 583dm. The islands reside along the southern
periphery of the attendant cold pool and observed 500mb temperatures
are approximately -9C and -10C at Lihue and Hilo respectively as of
12 UTC this morning. This low will sag southeast and tend to deepen
as the mid-latitude pattern eases southward during the next couple
of days. At the same time, energy associated with a progressive mid-
latitude trough will pinch off from the westerlies as it crosses
160W and close off in the vicinity of Kauai during Wednesday. The
islands, residing between these two rather small scale lows, will be
positioned below a narrow band of shortwave ridging aloft Wednesday
into Thursday. Attendant height rises in the mid-levels may
nonetheless be hard to come by as the overall geopotential height
field remains depressed and even further deepens given that the weak
low presently over/east of the Big Island is modeled to deepen to
579dm as it drifts eastward. As a consequence, little change in the
thermodynamic profile is anticipated today into Thursday with the
exception of the aforementioned upper-level ridging helping to quash
afternoon thunder potential over the Big Island. Moderate to locally
breezy trades will remain weakly stable during this time with
pockets of heavier showers developing where low-level convergence is
maximized, mainly Leeward Big Island along the sea breeze each
afternoon. Here, nuisance flooding is not out of the question.
By Thursday, lapse rates steepen to 6.5 to 7.0C/km over the western
end of the state, the GFS being notably colder and unstable aloft
compared to the EC which settles the low further west. Regardless of
the model differences, ridge amplification east of the Dateline will
cause trades to strengthen during this time limiting the potential
for areas of enhanced convergence to emerge anywhere except Leeward
Big Island. As a result, expect some variety of moderately unstable
trades to develop no later than Thursday and continue through at
least Friday night. From a sensible weather perspective, this
suggests quick-moving/transient trade wind showers some of which may
be heavy, especially at night and during the morning. The potential
for thunderstorms over leeward/interior portions of the Big Island
on Thurs/Fri will be evaluated going forward as this area stands the
greatest chance to experience organized heavy rainfall as diurnal
convection develops each afternoon.
&&
.AVIATION...
Trade winds will return to a more easterly direction tonight and
strengthen into the moderate to locally breezy range from Tuesday
onward as the ridge builds in north of the state. Expect passing
showers mainly over windward and mountain areas and along leeward
convergence cloud bands through Tuesday, with brief MVFR conditions
possible within any shower bands. No AIRMETs are currently in
effect.
&&
.MARINE...
Trades will persist through the weekend, with the strongest winds
expected late Wednesday and Thursday. Currently, a 1032 mb
centered nearly 1400 nm northeast of the state is driving moderate
to fresh trade winds. Surface low pressure will form far north of
the islands tonight and push the surface high eastward on
Tuesday. Meanwhile, another area of high pressure from the west
Pacific will move into the central Pacific, then stall far north
of Hawaii on Wednesday into Friday. As the new high moves in,
expect trade winds to increase to fresh to strong levels on
Wednesday or Thursday, when a Small Craft Advisory (SCA) will be
needed for the typically windy waters around the Big Island and
Maui. The high is forecast to retreat westward during the weekend,
favoring a decrease in winds.
Surf along south facing shores will remain just below seasonal
average into Saturday as pulses of south-southwest and southwest
swell move through. Surf will decline Sunday and remain small into
early next week.
East shore surf will remain near or just below seasonal average
during the next couple of days, followed by a slight increase
Thursday and Friday as trade winds build east of the islands. A
gradual decline in east shore surf is expected during the weekend
and early next week. Tiny surf will prevail along north facing
shores this week.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...JVC
AVIATION...TS
MARINE...Wroe
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office