941 
fxpq60 pgum 232017 
afdpq 


Area forecast discussion 
National Weather Service tiyan GU 
617 am chst Thursday Jul 24 2008 


Synopsis... 
an upper-level low is centered northeast of Guam near 18n152e... 
moving slightly south of due west. At the surface...Quikscat winds 
strongly hint at a weak trough east of the islands near 150e...and 
GFS winds also depict a weak trough there. Radar and Sat loops show 
that scattered showers and isolate thunderstorms are mainly west and south 
of the islands...with just a lingering batch of showers near Guam. 


&& 


Discussion... 
from satellite trends and an examination of output from the models 
it is evident that the main influence on weather for the marianas is 
the upper-level low and the weak trough that is its reflection at the 
surface. Brisk north winds aloft on the west side of the low are 
pushing most of the middle and upper cloudiness south and west of the 
marianas today...along with most of the showers. The GFS and UKMET 
bring the surface trough and the upper low through the islands Friday... 
then on to the west Friday night. GFS and UKMET are in fair agreement 
on a return to scattered showers and isolated thunder tonight into Friday 
as the surface trough passes...but it should be a low-end scattered event. 
With the upper low passing over late Friday...thunderstorms are possible 
through Saturday...but only isolate shower coverage Friday night through 
the weekend. We will have to keep an eye on the upper low...as scattered 
showers could last into the weekend if the low becomes more active 
in its eastern quadrant. 


&& 


Marine/surf... 
have re-instated a 2-foot secondary west swell in the grids through 
Saturday...mainly as input for generating the surf forecast on west 
facing exposures. That swell should Peter out around Sunday. 


&& 


Eastern micronesia... 
a weakening trade-wind disturbance will keep clouds and showers over 
Pohnpei this morning. Then drier trades already over Kosrae will 
provide fair conditions for both islands into Friday afternoon. 
Quikscat wind data indicates an area of increasing trade-wind 
convergence pushing westward just east of the dateline. This will 
begin to affect the southern Marshall Islands with increasing clouds 
and even an isolated thunderstorm by late tonight. Then showers and 
a few thunderstorms are likely through Friday night. 


The trade convergence zone will extend over Kosrae by Friday evening 
and over Pohnpei by Saturday...bringing inclement weather into early 
next week. Some improvement can be expected over Majuro during the 
weekend as the main convergence zone temporarily shifts slightly to 
the north. However....it should move back over the atoll by Monday 
with more wet weather. 


&& 


Western micronesia... 
fair weather will give way to cloudiness this evening over Chuuk as 
the remnants of a trade disturbance arrive from the east. Isolated 
showers with a slight threat of thunderstorms will be the worst this 
system can deliver into Friday. Nice weather is scheduled to return 
by Friday evening. Afterward...trade convergence spreading westward 
toward Chuuk will bring another slight chance for thunderstorms by Sunday. 


A weak surface ridge with subsidence aloft will continue over both 
Palau and Yap with unseasonably dry weather through Saturday. Then a 
TUTT cell moving west of the marianas might bring a few showers 
over the weekend. 


&& 


Gum watches/warnings/advisories... 
GU...none. 
Marianas waters...none. 
&& 


$$ 


Middlebrooke/chan