Area forecast discussion
National Weather Service Honolulu HI
1000 am HST Wednesday may 22 2013
Synopsis...
a pair of surface troughs to our north and northwest will keep winds
light over the state...with localized onshore sea breezes developing
again today. Clouds and showers will focus over the interior of the
islands this afternoon. The troughs will move west and gradually
dissipate...allowing a surface ridge to build north of the state.
Light trade winds will return Thursday...and strengthen through the
weekend.
&&
Discussion...
water vapor imagery shows an upper level low 800 miles
north-northeast of the state...with a trough extending to the west
southwest. At the surface...troughs are located within 300 miles
north and northwest of the state...with a high farther to the
northeast. 12z soundings from Hilo and Lihue show inversions of
7-9kft with precipitable waters of 1.3-1.4 inches...with the more
unstable and moist conditions at Hilo. Early morning mimic total
precipitable water imagery shows a band of moisture centered across
the islands...extending in a band northeast and west of the
state...with some drier air moving in toward The Big Island from the
east.
The surface troughs to the north and northwest of the state will
keep the gradient weak across the islands. The light winds allowed
widespread land breezes to develop last night...and will allow for
onshore sea breezes again this afternoon. Most islands started out
clear this morning...but are already starting to cloud up through a
combination of early diurnal activity and clouds south of the state
that have moved onshore. The atmosphere is slightly more stable than
yesterday...but there is enough low-level moisture and forcing along
sea breezes for interior showers this afternoon. Land breezes are
expected again for tonight...which should help clear out some areas.
However with the amount of moisture and clouds around offshore...
islands are not guaranteed to clear out and it is Worth keeping a
chance of showers overnight.
By Thursday the surface trough to the northwest will dissipate but
the trough north of the state will still persist. This trough will
limit the influence of the high to the northeast...but we will start
to see some semblance of trades return. Winds will be light
initially...which will allow lingering sea breezes across sheltered
leeward sections. However...clouds and showers should return to a
more typical trade wind pattern. The 12z GFS and European model (ecmwf) are both
similar in showing the trough to our north gradually diminishing
through the end of the week...with a surface ridge building north of
the state in its place. As this ridge builds in...trade winds will
steadily strengthen through the weekend. With upstream moisture
embedded within the strengthening flow...trade wind showers will be
somewhat more active than normal.
&&
Aviation...
VFR conditions prevail at all taf sites though volcanic emissions
may cause some local MVFR conditions at times. Daytime heating will
likely cause an increase in cloud coverage over land areas this
afternoon with some local MVFR conditions possible due to low clouds
and rain showers.
&&
Marine...
the south swell remains elevated...but continues its downward trend.
The current high surf advisory for south facing shores runs through
today...and surf will continue to gradually diminish through the
week. The current 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...
high surf advisory until 6 PM HST this evening for south facing
shores of all islands.
Wind Advisory until 6 PM HST this evening for The Big Island summits.
&&
$$
Discussion/marine...bravender
aviation...Burke
