Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 270213
Area Forecast Discussion
National Weather Service Honolulu HI
413 PM HST THU MAY 26 2016
A trough northwest of the area will move southeast slowly through
the weekend. The trough will keep the winds lighter than normal, so
daytime sea breezes and nighttime land breezes will prevail. The
sea breezes will bring clouds and showers to interior and leeward
areas through Sunday. A shower band will move south over the
islands through the middle of next week with trade winds returning
behind the band.
Typical May trade-wind weather will be absent through early next
week. The global models are in good agreement through the
Memorial Day weekend showing a persistent trough aloft north of
the area. This trough will keep the atmosphere unusually moist and
unstable for this late in the spring. A north to south surface
trough northwest of the islands will shift south slowly through
the weekend. That will keep the prevailing low level flow over the
islands light and generally out of the southeast. The southeast
flow will be partly blocked by the Big Island, so winds will be
light and variable over the smaller islands. Afternoon sea breezes
will produce clouds and showers over interior and leeward areas of
all the islands with partial clearing at night.
The GFS and ECMWF both show a new surface high moving east along
30N. Trade winds blowing out of this high will push a shower band
southeast across the islands during the middle of the week, with
moderate trade winds behind the front. The models are not in good
agreement on when the shower band will reach the islands so our
confidence is low on the timing for that feature.
The models suggest the trade winds returning next week will not
be very long and may even fade out again by the end of next week.
Afternoon clouds and SHRA have resulted in TEMPO MVFR and MT OBSC
in some locales. There is a chance we will have to extend AIRMET
Sierra for awhile past 04z, but expecting much of this activity to
settle down this evening as land breezes take over and result in
clearing and predominant VFR for many spots. The SE background
flow could still result in some isolated MVFR SHRA overnight,
particularly for windward areas. Daytime heating and SE background
flow will result in similar conditions from PM cloud buildups
(mostly over the island interiors) tomorrow.
Gentle winds and moderate swells are expected through next week,
so no small-craft-advisory conditions are expected.
A moderate southwest swell from the Tasman sea is expected to
peak Friday, then decline during the weekend. Since there are so
many islands along the path of the swell, surf is likely to be
inconsistent. A small northwest swell arriving Sunday will peak
Monday well below the advisory threshold. See the the
Collaborative Near-shore Swell and Wind Forecast (SRDHFO) for
details on this swell. Otherwise rather small surf is expected.