Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 271317
Area Forecast Discussion
National Weather Service Honolulu HI
317 AM HST FRI MAY 27 2016
A convective pattern will prevail through the weekend, especially
for the smaller islands, as a trough northwest of the islands
keeps winds light and from the southeast. Land and sea breezes
will form, causing clouds and showers to favor mauka and leeward
areas each afternoon and evening. Nights and early mornings will
be clearer and drier. A shower band will move south over the
islands through the middle of next week and trade winds are
expected to briefly return behind the band.
Except for drying things out a bit in the first period grids to
account for clearer conditions east of Kauai this morning, overall
forecast philosophy hasn`t changed much from last evening. A 1030 MB
surface high far northeast of the main Hawaiian Islands would
normally drive at least moderate trade flow across local waters.
However, a surface trough northwest of Kauai continues to push
into the southwestern flank of the high, slackening the pressure
gradient across the islands and causing winds to veer to
southeasterlies. The overnight Lihue sounding showed PW near 1.6
inches with an LI of minus 1. This is moist and unstable enough
to support brief bouts of enhanced showers across Kauai. However,
conditions are drier and more stable across eastern portions of
the chain, where fewer showers were noted overnight.
Satellite loop shows an upper trough persists north of the area.
Models show this feature will be with us into early next week,
acting to keep the atmosphere unusually moist and unstable. The
surface trough northwest of Kauai will shift south slowly through
the weekend. This will keep 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.
Models show a new surface high will move east along 30N. Trade
winds driven by this high will push a shower band southeast
across the islands during the middle of next week, with moderate
trade winds expected to arrive behind the front. However, models
are not in good agreement on when this shower band will reach the
islands so timing confidence is low. We expect that trade winds
returning next week behind the front will not last long and may
fade out again by the end of next week.
A weak wind regime will remain in place today and tonight across
the western half of the state, with daytime sea breezes and
overnight land breezes expected in most areas. Across the eastern
half of the state, light trade winds are expected to prevail.
Some enhanced showers will result in reduced cigs/vsbys across
much of Kauai early this morning. Elsewhere, predominantly VFR
conditions are expected through the morning hours. Showers are
expected to develop over the mountains and interior of the islands
this afternoon, bringing some reduced cigs/vsbys to these areas,
particularly across Kauai.
Airmet Sierra is in effect for mountain obscuration across Kauai.
These conditions will likely continue through much of the day. The
Airmet may need to be expanded to include some of the other
islands this afternoon.
Winds and combined seas will remain below small craft advisory
criteria through the forecast period.
A moderate southwest swell from the Tasman sea is expected to
peak today, 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.