479 
fxhw60 phfo 282005 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
1005 am HST Thursday Aug 28 2008 


Synopsis... 
light to moderate trade winds are expected through the Holiday 
weekend...bringing brief showers to windward slopes. In addition... 
clouds and a few showers will develop over leeward areas in the 
afternoons...before clearing in the evenings. 
&& 


Discussion... 
no big surprises in store today. Winds will be light enough for 
afternoon sea breezes to set up...which will likely lead to some 
afternoon showers over leeward areas...similar to what set up 
yesterday. At this time there have been no changes to the forecast. 


Previous discussion follows. 
&& 


Previous discussion... 
issued at 330 am 
currently a 1026 mb high center lies about 1500 miles northeast of 
the islands...with its attendant ridge extending west-southwest from 
the center. South of the ridge...and over the islands...light to 
moderate trade winds prevail. A weak trough tracking westward within 
the trade flow lies between the islands and this high...keeping the 
the local pressure gradient loose. Low-level moisture approaching 
with the trades is capped beneath the subsidence inversion...which 
was measured near 8 thousand feet in Lihue early this morning... 
while Hilo/S balloon was launched through a moister air 
mass/shower...with the inversion not apparent until about the 12 
thousand foot mark. Satellite imagery shows little in the way of 
moisture directly upstream of the smaller islands...with the least 
near Kauai. Some windward gages on The Big Island got over 3/4 of an 
inch of needed rain overnight....but this moisture is expected to 
decrease as the day wears on. 


Surface high pressure will remain anchored in the northeast Pacific 
through the Holiday weekend and into next week...providing the 
islands with a steady...but somewhat moderated...trade wind flow. 
The high will be weakened and reinforced a couple of times over this 
time frame...resulting in slight fluctuations in local wind 
speeds...but the expected large scale trade flow over the islands 
can be broadly characterized as moderate. Trade winds were light 
enough to allow sea breeze-driven showers to develop over leeward 
areas of Oahu and Maui yesterday...and with winds remaining on the 
lighter side...have included increased leeward probability of precipitation and sky cover in 
the forecast for both today and tomorrow. 


Although a middle-level ridge will prevail far north of the islands 
through next week...a pair of middle-level lows are forecast to develop 
south of this ridge...both northeast and southwest of the islands. 
The weak surface reflections of these lows will loosen the low level 
gradient...and keep trade winds from exceeding moderate speeds. 
These lows will also act to weaken the subsidence inversion and 
allow trade showers...and afternoon leeward convection...to become a 
little more active next week. In the shorter term...both GFS and 
European model (ecmwf) continue to /believably/ indicate that moisture currently near 
25n148w will move across the islands from the northeast...bringing 
increased trade showers late Friday. 




&& 


Hfo watches/warnings/advisories... 
none. 
&& 


$$