Weather

801 
fxhw60 phfo 131405 
afdhfo 


Area forecast discussion 
National Weather Service Honolulu HI 
400 am HST Monday Oct 13 2008 


Synopsis... 
a surface front approaching the islands from the northwest will 
produce numerous showers...with locally heavy rainfall possible...on 
Kauai and Niihau from this afternoon into Tuesday. Elsewhere... 
southeasterly winds will likely result in the development of upslope 
showers over the rest of the state from Oahu to The Big Island later 
today and Tuesday. Expect more typical trade wind weather to 
gradually return to the islands by the end of the work week. 


&& 


Discussion... 
the latest water vapor imagery indicates an upper tropospheric low 
has developed near 30n 158... about 575 miles north of 
Honolulu. This new feature aloft appears to have been moving slowly 
toward the south southwest during the past few hours. There is also 
a trough axis extending toward the southwest to another newly formed 
small upper tropospheric low near 23n 175w. This second low is 
propagating toward west southwest at about 10 miles per hour. 


At the surface...the ocean prediction center is analyzing a 1016 mb 
surface low near 31n 154w early this morning. A front extends south 
from this low to a point about 150 miles due north of Kauai to 
another point about 300 miles west of Kauai. The poorly defined 
leading edge of this front appears to shifting toward the south 
southeast at 15 to 20 miles per hour. 


The 0600 UTC NAM run appears to show this front will slow down 
before it reaches Kauai late this afternoon or early this evening. 
The front is then expected to remain stalled in the vicinity of 
Kauai tonight. The global models eventually weaken the front to a 
trough that begins to move slowly west away from the state Tuesday. 
In the meantime...the low-level flow across the Hawaiian islands 
will be light today...before shifting to the southeast tonight. 


Kauai and Niihau appear to have the greatest chance for wet 
weather...with locally heavy rainfall possible over these islands 
later today and tonight. The remainder of the Hawaiian islands will 
be in the relatively moist southeasterly prefrontal flow. This is 
expected to cause an increase in shower coverage along the south and 
southeast facing slopes of the islands from Oahu to The Big Island. 
There is also a possibility of additional showers developing within 
convergent bands east of the front. 


As the trough...or former front...begins to move west away from the 
islands...our surface winds will gradually shift to a more easterly 
direction. However...we may not see a typical trade wind weather 
returning until Thursday or Friday. This is due to the continued 
atmospheric instability that is expected to remain across the 
islands due to the influence of the upper tropospheric low and 
trough aloft in the vicinity of the islands Tuesday and Wednesday. 


By the end of the work week...the GFS model indicates a subtropical 
ridge will be in place far north of the state. This ridging should 
keep US in a more typical trade wind weather pattern into the 
upcoming weekend. 


&& 


Marine... 
a large north northwest swell continues to affect most of the 
smaller Hawaiian islands this morning. Buoy 51001...or buoy one... 
reported a swell height of 10 feet with a period of 14 seconds at 
300 am HST. Surf heights will continue at or above the high surf 
advisory thresholds along north and west facing shores of Kauai and 
Niihau...and along north facing shores of Oahu...Molokai and Maui 
today and tonight. The wavewatch iii model continues to indicate 
this swell may remain large enough to produce advisory level surf 
into Tuesday. This again depends on the movement of the low that is 
currently located north of the Hawaiian islands. 


The north northwest swell appears to be large enough to generate 
combined seas of around 10 feet in the marine zones north and 
northwest of Kauai. This prompted the issuance of a Small Craft 
Advisory /sca/ for the northwest and windward Kauai coastal waters 
yesterday. Data from the mokapu buoy located just offshore from 
Kailua on Oahu indicated that combined seas are less than 7 feet 
north of Oahu. With the lighter winds today...expect the 
contribution from the wind waves to continue to diminish. The 
anticipated return of slightly stronger winds later tonight and 
Tuesday may result in the inclusion of additional marine zones 
around Kauai and north of Oahu in the Small Craft Advisory later tonight or Tuesday. 


&& 


Hfo watches/warnings/advisories... 
high surf advisory through 6 PM HST Tuesday for north and west 
facing shores of Niihau and Kauai...and north facing shores of 
Oahu...Molokai and Maui. 


Small Craft Advisory through 6 PM HST Tuesday for the northwest and 
windward Kauai coastal waters. 


&& 


$$ 


Houston