Area forecast discussion
National Weather Service Honolulu HI
400 PM HST Monday may 20 2013
Synopsis...
an unseasonably strong area of low pressure several hundred miles
north of the state will maintain a land and sea breeze pattern into
Wednesday. A band of moisture associated with the low will keep
rain chances slightly higher over the eastern end of the state
through tomorrow...with the best odds for showers occurring in the
afternoon hours. Trade winds will rebuild Thursday and Friday...with
unsettled trade wind weather possible this weekend.
&&
Discussion...
a light wind...land and sea breeze convective pattern prevails as a
relatively rare...mid-may cutoff low meanders about 425 miles north
of Oahu. A ragged...dissipating frontal band is stalled over Maui
County while another band marking an area of convergence is
lingering just east and northeast of The Big Island. This has
positioned a bit more moisture over the eastern end of the state...
about 0.4 of an inch more precipitable water than noted on the Lihue
sounding...but afternoon sea breezes have produced only spotty heavy
showers over The Big Island and Maui County. Oahu has seen little
shower activity...while rainfall on Kauai has been produced by
northerly winds pushing up on mountain slopes. Shower chances will
diminish overnight on the islands as land breezes lead to partial
clearing.
The convective land and sea breeze pattern will hold Tuesday and
Wednesday. The cutoff low will drift northward and gradually fill. A
band deep moisture marking low level convergence is expected to
linger near or just east of The Big Island and slowly dissipate.
Meanwhile....the old frontal boundary may provide some additional
moisture to fuel rainfall across the central islands Tuesday and
Kauai on Wednesday. The placement of these features will determine
if showers get a boost...especially as afternoon sea breezes fuel
convection.
As the cutoff low gradually fills...high pressure settling far
northeast of the state will cause trade winds to slowly rebuild.
Expect a return to a typical...late-Spring pattern of windward and
Mauka showers.
Heading into the weekend...trades will become locally breezy.
Windward and Mauka showers will prevail...although models are
hinting at atn enhancement to showers as a weak upper low develops
overhead.
&&
Aviation...
at least for the smaller islands...VFR is the primary flying conditions
for the rest of this afternoon and this evening/S weather. The afternoon cloud
bases over interior and mountain areas are pretty much above MVFR
criteria...and the rain showers have isolate so far. We likely will be able to
get by without issuance of an airmet for mountain obscure. Any MVFR ceilings
are local or isolate and not widespread. The Big Island is a little
more challenging but appears the rain showers are most active on the Lee
side mainly SW of Kamuela Waimea area. Rain showers are isolate in coverage
elsewhere around The Big Island. A solid...strong SW wind flow across
Lee side Big Island may limit rain showers activity to isolate...plus that
the ceilings are mainly above MVFR level. Will continue to monitor closely
for MVFR conds
&&
Marine...
the south swell remains as the main story across Hawaiian waters as
winds will be below Small Craft Advisory...sca...levels through at
least Thursday. The high surf advisory for south facing shores has
been extend through Tuesday afternoon...and will remain elevated
into Wednesday. Nort facing shores will also see a boost to near
advisory levels on Wednesday. Small Craft Advisory level winds are expected to
develop by Friday or Saturday.
&&
Hfo watches/warnings/advisories...
high surf advisory until 600 PM HST Tuesday for south shores of
all islands.
Wind Advisory in effect for Big Island summits until 6 PM HST
Tuesday.
&&
$$
Discussion/marine...wroe
aviation...lau
