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Area Forecast Discussion
National Weather Service Tiyan GU
314 PM ChST Fri Jul 29 2016

Mostly dry and sunny conditions have been seen across the Marianas
for much of the day with the exception of some showers off to the
west of Guam. Light winds have been out of the east and those winds
were just strong enough to push clouds and showers related to island
convection off shore to the west. Upper-air sounding indicated 2.23
inches precipitable water, which is sufficiently moist for
thunderstorms, but much drier air and wind shear above 15 thousand
feet have made it tougher for deep convection to develop. Southeast
of the Marianas, a surface trough is passing westward through Chuuk
State, while a couple of circulations are seen well north of the far
northern Marianas and northwest of Wake Island. A slowly-developing
depression is found well northwest of Koror.


Considering the fairly lengthy synopsis, not much change was needed
for the forecast. Decided to extend isolated thunderstorms through
Monday night as models show convection lingering behind the trough
that will reach the Marianas this weekend. The broad circulation
approaching the Philippines will not affect the Marianas. For next
week, models continue to dance around how the circulations north of
20N will indirectly affect the Marianas. GFS and ECMWF winds range
from southwest to west around midweek as they each show circulations
north of 20N moving to the northwest, staying well north of the
Marianas. ECMWF continues to be the aggressive model, showing more
precip over the area than does the GFS. For seas, little change is
expected from combined seas of 3 feet, a small east swell, and a low
risk of rip currents the next several days.


.Eastern Micronesia...
A series of trade-wind disturbances continue to generate scattered
showers and isolated thunderstorms across the eastern region from
Pohnpei to Majuro. Isolated showers and a few thunderstorms are seen
in the vicinity of Weno, Chuuk. A pattern of moist, southeast flow
converging with east trades along 8N to 10N will persist the next few
days. An upper-level trough just north of the region will keep upper
level conditions conducive to heavier showers and thunderstorms at
least through Saturday. GFS shows the convergence boundary lifting
north by early next week allowing drier weather to build in across
the region.


.Western Micronesia...
Reasoning for the Chuuk forecast can be found in the Eastern 
Micronesia discussion above.

A slowly-developing tropical disturbance is still located northwest
of Koror near 11N129E. A monsoon trough heads southeastward between
Yap and Koror to near EQ143E. Koror has seen a lull in showers today,
but showery conditions will persist the next day or two with moderate
monsoon flow over the republic. Much drier weather is seen near Yap
where weak ridging is situated over the island. A wet monsoon pattern
will continue the next couple days at Koror with ridging building in
over the republic by late Sunday or Monday as the disturbance lifts
northward away from Yap and Koror. Expect drier weather early next
week with winds light and variable at times. Bumped up seas at Koror
to between 4 and 6 feet in response to the moderate monsoon winds
there. Seas will diminish 1 to 3 feet next week.


Marianas Waters...None.


W. Aydlett/M. Aydlett

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