Area Forecast Discussion
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FXPQ60 PGUM 302105

Area Forecast Discussion
National Weather Service Tiyan GU
705 AM ChST Sun Jul 31 2016

Gentle winds and isolated showers prevail across the Marianas this


A very weak trough to the east of the Marianas is moving much
slower toward the islands than previously expected. This will
result in less likelihood of thunderstorms over the Marianas,
especially today. Chose to change thunder to slight chance for
today, but left isolated thunderstorms in the forecast for tonight
through Monday night for now. Otherwise, no major changes made to
the inherited forecast. Models remain divided concerning rainfall
for the long term. GFS and ECMWF continue to show a broad monsoon
circulation moving through the northern CNMI later in the week.
The difference continues to be the amount of anticipated rainfall
and winds. GFS remains the dry solution with lighter winds. Chose
to maintain the model blend forecast for winds for now along with
the drier bias of the GFS. Adjustments are likely over the next
few days as this system begins to evolve.


.Eastern Micronesia...
The combination of an upper-level trough and a few weak trade-wind
disturbances will continue to spark off a few showers and
thunderstorms near Chuuk and Pohnpei thru Monday night, Kosrae
thru Monday and Majuro on Monday. A subtropical low centered
northeast of Wake Island near 21N158E and its associated trough
are gradually moving westward over the next few days. A surface
ridge has formed east of these features, north of 10N and east of
160E. Model guidance is suggesting this low might further develop
into a monsoonal system near the northern Mariana Islands toward
midweek. Under this scenario, the surface ridge southeast of the
low will dig southward over Chuuk, Pohnpei and Kosrae. This should
promote fair weather for these locations near Tuesday and
Wednesday. For Majuro, it will be too far east to be directly
affected by the ridge. Instead, converging northeasterly trade
winds are expected to form which will increase the chance of
showers. As the monsoonal system begins to track northward after
midweek, it will lift the ridge northward and allow converging
northeast trades to spread showery conditions westward into
Kosrae, Pohnpei and Chuuk.


.Western Micronesia...
Discussion for the Chuuk forecast can be found in the Eastern
Micronesia section above.

The southeastern end of a monsoon trough near 138E is slowly
drifting westward toward Koror this morning. Anticipate showers
and thunderstorms related to it reaching Koror by later this
afternoon. For Yap, an upper-level low will keep a few
thunderstorms around thru Monday. This same low will also sustain
unstable weather near Koror thru Monday afternoon. By Monday
night, a surface ridge from the east should usher in gentle winds
and partly cloudy skies for the area.


Marianas Waters...None.


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