Weather

218 
fxhw60 phfo 291912 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
930 am HST Friday Aug 29 2008 


Synopsis... 
high pressure north of the islands will keep moderate trade winds 
blowing through the Holiday weekend...and into next week. Trade 
showers will increase tonight...then diminish slightly Saturday and 
Sunday. Trade showers may increase again on Labor Day and Tuesday as 
an upper low passes over the islands. The trades will carry a few 
showers to the leeward areas of the smaller islands at times. 


&& 


Discussion... 
latest surface analysis shows a sprawling 1031 mb high centered far 
north of the state. The resultant pressure gradient is spilling 
northeast trades across the islands this morning. Observed wind 
speeds remain on the light side with moderate winds through the 
channels and over terrain features. Local gusty winds are being 
funneled over the Haleakala Summit with earlier gusts over 50 miles per hour. 
These winds have backed off slightly but still with winds at or near 
advisory level. Will allow the continued downward trend in observation and 
forecast model data to play out this morning and no advisory is 
required at this time. 


At the upper levels...the ridge near the islands continues to weaken 
and pull north allowing weak troughing at 500 mb to develop. This is 
apparent in water vapor imagery and picked up by the model data. 
The airmass remains Bone dry aloft however and the only immediate 
affect of this trough overhead will be to raise the marine layer 
inversion...which stands at 8 k feet at Lihue and 10 k feet at Hilo 
this morning. This will make it possible for trade moisture to 
develop into slightly deeper convection with heavier showers 
possible. 


Looking upstream...there is an area of cumulus depicting a band of 
moisture approaching the islands from the northeast. This band 
should reach The Big Island and Maui this afternoon and the rest of 
the islands this evening. Expect an increase in the windward and 
Mauka shower activity as this band passes. Farther upstream...there 
are lots of cumulus present...but little organization is seen. 
These trade showers will continue through the weekend...with little 
impact to the leeward sides expected. 


The 12z GFS indicates the weak upper trough will hang over the 
islands through the weekend and even deepens the trough slightly 
just west of the islands by Labor Day. This will likely deepen the 
mixed layer more and allow for wetter trades for the Holiday into 
Tuesday. 


After that the upper ridge is forecast to build in again across the 
islands Wednesday through next week with a drier boundary layer and 
drier trade wind weather expected. 


&& 


Marine... 
winds in the windier marine zones are expected to remain just below 
small craft criteria today. Not much significant swell expected for 
the next several days...but a solid south-southwest swell is in the 
process of being created east of New Zealand...with a 1043 mb high 
forecast to pair up with a 985 mb low over the next two 
days...thereby stirring up some large seas. Wave watch iii indicates 
this swell will arrive around the middle of next week...building to 
advisory heights Thursday and Friday. 


&& 


Hfo watches/warnings/advisories... 
none. 


&& 


$$ 


Brenchley