Area Forecast Discussion
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FXPQ60 PGUM 292055
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Area Forecast Discussion
National Weather Service Tiyan GU
655 AM ChST Sat Jul 30 2016

.Synopsis...
A quiet morning for the Marianas, with gentle trades and isolated
showers. The buoys are still reporting seas just under 3 feet.

&&

.Discussion...
With the ECMWF and GFS finally coming into good agreement on the
overall pattern for the next week or so, have reworked the
forecast to base it on a broad quasi-monsoonal circulation
developing Tuesday and Wednesday NE of the Marianas near 20N150E,
with a monsoon tail extending southwest from it through the
Marianas. The ECMWF is stronger with it than the GFS, and takes
the resulting tropical cyclone faster towards Japan next week. As
far as the Marianas are concerned, have used ECMWF winds beginning
tonight, all the way out to Day 10, but starting the middle of
next week have reduced those winds by about 25 pct, as the ECMWF
seems too strong by that point. The ECMWF brings more rainfall
to the area than the GFS, mainly next week, but has been varying
quite a bit from run to run, while the GFS seems dry for such a
situation. So the jury is out on that question, and will leave
next week isolated for now after Monday night. All that can be
said is that there is some potential for heavy rain by the middle
of next week.

&&

.Marine...
Have refreshed the marine grids, mainly to add a WSW swell at 1 to
2 feet for Sunday night through Wednesday, generated by Tropical
Depression 06W east of the Philippines. Also, 4-ft seas are
creeping back into the eastern waters through Monday.

&&

.Eastern Micronesia...
There is a pair of subtropical low pressure systems, one centered
east of Iwo To Island at 25N147E and another one centered east of
Minami Tori Shima at 24N160E. These systems are becoming better
organized and beginning to draw stronger trade winds from near the
Date Line northwestward away from Eastern Micronesia. This has
significantly weakened the low-level convergent boundary near Kosrae
and the Marshall Islands. As a result, pockets of convection seen
last evening near both locations have dissipated.

However, a few weak trade-wind disturbances from Chuuk State eastward
to the Marshalls along with a modest upper-level trough near 10N are
still present. These features will maintain a few showers and a
thunderstorm or two near Chuuk and Pohnpei thru this evening and also
on Monday. Similar conditions are also expected for Majuro today and
Kosrae from Sunday night to Monday. As the subtropical lows develop
further and start to consolidate near Tuesday, they will cause the
tropical ridge axis currently near 17N150E to sink southward
closer to 10N and provide fair weather near Chuuk and Pohnpei. On
the other hand, this will cause southeast trade winds near the
Date Line to back northeast toward the Marshalls and Kosrae. This
should increase trade-wind convergence and the chance of showers
near both places toward midweek.

&&

.Western Micronesia...
The Chuuk forecast discussion is in the Eastern Micronesia
discussion above.

TD 06W, previously located at 12N129E, has drifted farther
northwest to near 13N127E this morning. In response, the fresh
converging southwest monsoon winds feeding toward TD 06W has also
shifted westward away from Koror. Therefore, scattered showers are
no longer expected today but modest southwest winds can still
spark off isolated thunderstorms near the capital. As TD 06W
continues to drift northwestward tonight and Sunday, the monsoon
trough axis associated with it will drape over Koror and bring a
period of widely scattered showers. For Yap, gentle winds and
subsidence related to an approaching upper-level low should
prolong dryness thru this evening. By early Sunday morning,
isolated thunderstorms near the upper low center will impact the
island thru Sunday night. This same upper low is also going to
prolong instability near Koror thru Monday. Assuming TD 06W will
further develop near the northern Philippines early next week, a
surface ridge should form to its southeast. If so, variable winds
and partly cloudy skies will prevail across both locales.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
Marianas Waters...None.

&&

$$

Middlebrooke/Chan



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