723 
fxhw60 phfo 212009 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
1010 am HST Thursday Aug 21 2008 


Synopsis... 
high pressure to the north will maintain moderate to fresh trade 
winds over the islands through the forecast period. The trades will 
bring clouds and showers that will affect mainly windward and Mauka 
areas...with a few reaching the Lee areas of the smaller islands at 
times. 


&& 


Discussion... 
currently an east to West Ridge of high pressure lies along 34n... 
about 800 miles north of Kauai...with an embedded 1027 mb high 
centered north-northwest of the islands near 34n 163w. Moderate 
trade winds prevail over open water south of this ridge...as 
highlighted by this morning/S Quikscat pass...which showed 15 to 20 
knots east-northeast winds. As usual...these winds are subject to local 
accelerations and decelerations over and near the islands...due to 
terrain and heating. Water vapor imagery shows relatively dry air 
aloft over the islands...but overnight soundings showed a deep mixed 
layer...with the inversion base as high as 10 kft in Lihue/S 
sampling. Showery cloud clusters are seen moving along with the 
trade flow...with one such cluster moving over Oahu as of this 
writing. Additional shower areas are seen upstream...in the form of 
open-celled cumulus elements...thus trade showers remain throughout 
the forecast. 


Little change to the ongoing forecast philosophy...with high 
pressure north of the islands persisting through the forecast 
period. The surface ridge axis will remain nearly stationary in its 
current position into Saturday...after which it/S eastern 
extent...far northeast of the islands...will be shunted slightly 
southward by a front. The high centered nearly due north of the 
islands now will take up a position to the northwest in response... 
with little expected change in local wind speed or direction. High 
pressure will reestablish/reorganize far northeast of the islands 
early next week as the front weakens...thereby maintaining at least 
a moderate trade flow through the forecast period. 


A weak middle- and upper-level low/trough...currently east of the 
islands along 146w/147w...will track westward and pass over the 
islands around Saturday. This feature may be responsible for our 
current higher than normal inversion height...and will act to keep 
the inversion height slightly elevated into the weekend. Deep 
moisture is lacking...so although trade showers may be a little more 
active in the short term...their total rainfall will be limited as 
they track steadily west...and they will be capped. 


Overall...seasonable weather in the works...and typical August trade 
wind weather will prevail. 


&& 


Hfo watches/warnings/advisories... 
none. 


&& 


$$ 


Birchard