975 
fxhw60 phfo 211342 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
342 am HST Sat Nov 21 2009 


Synopsis... 
trade winds will continue through the weekend as high pressure 
remains far north of the islands. Showers will focus on windward 
and mountain slopes...with a few showers reaching leeward 
locations. Trades will weaken slightly early next week. 


&& 


Discussion... 
rainfall continues sparse overnight with the Hawaii rain gage 
network only showing light rainfall over the windward Big 
Island. Gages along the northeast lower slopes of The Big Island 
ranged from zero to a quarter of an inch while windward gages on 
the smaller islands did not see any rainfall. The dry weather is 
expected to continue today...and the pop grids reflect 
this...representing a dry trade weather regime of scattered 
showers and cloudy skies over windward areas...with mostly clear 
skies and a small chance of showers over leeward locations. 


The overnight soundings from Lihue and Hilo are similar to Friday 
afternoons/ showing a dry atmosphere with precipitable water 
values near one inch...which is in Stark contrast to the two inch 
precipitable water values during last weekend/S flood event. Precipitable water values are 
expected to slowly increase over the weekend...and into next 
week...bringing a more climatological trade wind weather pattern 
..with showers increasing over windward locations. 


A 1027 mb high pressure far north of the state is maintaining the 
fresh to strong trade winds across the islands. Storm systems 
racing across the North Pacific are forecast to push the high 
toward the east and its associated surface ridge south over the 
weekend and next week... thereby relaxing the pressure gradient 
over the state and decreasing the trade winds into the moderate to 
fresh range early next week. 


The GFS and European model (ecmwf) both show a weak cold front approaching Kauai 
Tuesday night and Wednesday...but never reaching the Garden Isle. 
The models do show tropical moisture being drawn up from the south 
in response to the front...increasing precipitable water values near The Big 
Island Tuesday night...and then Maui County and Oahu on Wednesday. 
This scenario would bring increasing showers to windward areas of 
those islands. However...previous model runs had shown a surface 
trough or even a weak surface low accompanying this moisture...so 
the models have been trending toward a weaker feature over the 
past few days. The weakening trend does not Bode much confidence 
in this feature...so the forecast remains with climatology trade wind 
weather. 


&& 


Marine... 
a large northwest swell is expected to begin filling in Saturday 
night...likely reaching advisory levels Sunday and Monday then 
slowly lowering into Tuesday. A larger northwest swell is expected 
to fill in Tuesday night...and peak late Wednesday or Wednesday 
night. 






&& 


Hfo watches/warnings/advisories... 
Small Craft Advisory until 5 PM HST Sunday for Kauai Channel- 
Kaiwi Channel-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big 
Island leeward waters-Big Island southeast waters. 




&& 


$$ 


Morrison