Area forecast discussion
National Weather Service Honolulu HI
830 PM HST Wednesday may 22 2013
Synopsis...
a pair of surface troughs north of the islands are keeping a light
wind regime across the islands through Thursday. Sea breezes will
likely bring more afternoon showers on Thursday with best chances
of rain over interior and mountain areas. Light trades will begin
establishing late Thursday...then a more typical trade wind weather
regime will return for the upcoming weekend.
&&
Discussion...
latest WV satellite data shows an upper level trough low located some
800 miles north of the main Hawaiian islands...while surface analyses show
two decaying troughs within 300 miles north and northwest of the island chain.
Meanwhile...a surface high remains centered far to the NE of the
islands. This synoptic scenario is keeping generally light winds
across the area with remnant convection from earlier sea breeze
activity still lingering over central Oahu...leeward Haleakala in
Maui...and the southeast slopes of Mauna Loa over The Big Island. Most of
this convective activity should clear out after midnight as land
breezes intensify. However...with latest soundings showing precipitable waters
around one and a half inches...enough moisture will remain in place
tonight for some isolated showers to linger into the overnight
hours.
The aforementioned surface troughs will continue to decay on Thursday...but
their influence will still keep weak gradients over the islands.
Thus...the expected return to a trade wind pattern will be slow with
weak NE/east flow starting to establish Thursday afternoon...and gradually
intensifying towards the end of the week. Therefore...another round
of afternoon sea breezes is likely again Thursday afternoon and evening
with showers favoring interior and mountain areas. As the troughs
dissipate and high pressure strengthens NE of the islands...a more
typical trade wind weather regime will return for the upcoming
weekend. GFS and European model (ecmwf) show fair agreement in this overall scenario
with upstream moisture feeding windward and Mauka showers as the
trades establish.
&&
Aviation...
partial clearing should occur over the islands while the coastal
waters may see an increase in low clouds overnight.
Hence...prevailing VFR conditions are expected at all taf
sites...though may see some local MVFR visible conditions in the
vicinity of phto due to volcanic emissions...and brief MVFR ceilings
are possible over coastal waters.
&&
Marine...
the south swell will keep decreasing and remaining below advisory
criteria during the next several days. A northwest swell is near its
peak and will last into Thursday before gradually diminishing.
Trade winds will strengthen through the week...and are expected to
reach Small Craft Advisory levels over the windier locations near
Maui County and The Big Island by the weekend.
&&
Hfo watches/warnings/advisories...
Wind Advisory until 6 am HST Thursday for Big Island summits.
&&
$$
Discussion/marine...reynes
aviation...lutu-mcmoore
